WO2024048179A1 - Superconducting magnet device and nuclear magnetic resonance diagnosis device - Google Patents

Superconducting magnet device and nuclear magnetic resonance diagnosis device Download PDF

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Publication number
WO2024048179A1
WO2024048179A1 PCT/JP2023/028156 JP2023028156W WO2024048179A1 WO 2024048179 A1 WO2024048179 A1 WO 2024048179A1 JP 2023028156 W JP2023028156 W JP 2023028156W WO 2024048179 A1 WO2024048179 A1 WO 2024048179A1
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superconducting
current
magnet device
coil
temperature
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PCT/JP2023/028156
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French (fr)
Japanese (ja)
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毅 和久田
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株式会社日立製作所
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F6/00—Superconducting magnets; Superconducting coils
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F6/00—Superconducting magnets; Superconducting coils
    • H01F6/04—Cooling

Definitions

  • the present invention relates to a superconducting magnet device that generates a high magnetic field and utilizes the magnetic field, and a nuclear magnetic resonance diagnostic device.
  • a superconducting magnet device can generate a higher magnetic field than permanent magnets or normal conducting electromagnets. For this reason, superconducting magnet devices are widely used as ultra-high magnetic field magnets for research, magnets for analysis devices such as NMR (nuclear magnetic resonance), and magnets for medical MRI (Magnetic Resonance Imaging). .
  • the operating modes of superconducting magnet devices are broadly classified into two (see, for example, Patent Document 1).
  • the first operation mode is a power drive mode in which a magnetic field is generated by supplying current from the power supply to excite the magnet, and the current continues to flow from the power supply during operation.
  • a superconducting circuit is constructed by installing a persistent current switch (PCS) in the superconducting magnet, a current is applied to the superconducting circuit from the power source to generate a magnetic field, and then the current is supplied from the power source.
  • PCS persistent current switch
  • persistent current mode which operates while disconnected from the power supply, there is no noise intrusion from the power supply, so a temporally stable magnetic field can be obtained.
  • applications such as NMR and MRI that utilize this property and particularly require stability of the magnetic field, conventional wisdom has believed that operation in persistent current mode is essential.
  • the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a superconducting magnet device and a nuclear magnetic resonance diagnostic device that can realize a temporally stable magnetic field in drive mode operation.
  • a superconducting magnet device is a superconducting magnet device comprising a superconducting coil around which a superconducting wire is wound, and a power source for exciting the superconducting coil, A switch element and a protective resistor are connected in parallel to the coil, and the switch element is made of a high-temperature superconductor wire, and the current capacity of the switch element is greater than the rated operating current of the superconducting coil.
  • the switching element is sufficiently small and electrically shorts the superconducting coil in a low resistance state when a predetermined magnetic field is being generated, and in a high resistance state when the magnetic field is changing.
  • the main feature is that the superconducting coil operates to spontaneously change its open/close state by changing the amount of current supplied from the power source to the superconducting coil.
  • a temporally stable magnetic field can be realized in drive mode.
  • FIG. 1 is a circuit diagram showing the basic configuration of a superconducting magnet device according to an embodiment of the present invention.
  • FIG. 2 is a circuit diagram showing the basic configuration of a superconducting magnet device according to a comparative example. 1 is a conceptual diagram showing a basic mounting state of a superconducting magnet device according to an embodiment of the present invention.
  • FIG. 2 is an equivalent circuit diagram for explaining magnetic field stabilization realized by the superconducting magnet device according to the embodiment of the present invention.
  • FIG. 3 is a diagram showing temporal changes in currents flowing through each of an excitation power source and a superconducting coil during the excitation process of the superconducting magnet device according to the embodiment of the present invention.
  • FIG. 2 is a diagram showing temporal changes in currents flowing through each of an excitation power source and a superconducting coil during a demagnetization process of a superconducting magnet device according to an embodiment of the present invention.
  • FIG. 4 is a diagram showing temporal changes in currents flowing through each of an excitation power source and a superconducting coil in a current adjustment process of a superconducting magnet device according to an embodiment of the present invention.
  • FIG. 6 is a diagram showing temporal changes in currents flowing through each of the excitation power source and the superconducting coil when the superconducting magnet device according to the embodiment of the present invention is subjected to pre-energization operation.
  • FIG. 4 is a diagram showing temporal changes in currents flowing through each of an excitation power source and a superconducting coil in a current adjustment process of a superconducting magnet device according to an embodiment of the present invention.
  • FIG. 6 is a diagram showing temporal changes in currents flowing through each of the ex
  • FIG. 1 is a conceptual diagram showing a first mounting state of a superconducting magnet device according to an embodiment of the present invention. It is a conceptual diagram showing an example of operating temperature setting concerning a superconducting bypass element. It is a conceptual diagram showing an example of operating temperature setting concerning a superconducting bypass element. It is a conceptual diagram showing the 2nd mounting state of the superconducting magnet device concerning an embodiment of the present invention. It is a conceptual diagram showing the 3rd mounting state of the superconducting magnet device concerning an embodiment of the present invention.
  • FIG. 1 is an explanatory diagram showing a nuclear magnetic resonance diagnostic apparatus using a superconducting magnet device according to an embodiment of the present invention.
  • HTS high temperature superconductors
  • REBCO rare earth elements
  • BSCCO rare earth elements
  • MgB 2 magnesium diboride
  • the high-temperature superconductor HTS has a high critical temperature, and by utilizing this property, it is operated in a temperature range where the specific heat is an order of magnitude higher than that of liquid helium. Therefore, high-temperature superconducting magnets (HTS magnets) can be put to practical use in that they have an order of magnitude larger quench energy margin than LTS magnets against the normal conduction transition phenomenon (quench) caused by thermal energy input into the superconducting magnets due to disturbances. It is expected that
  • a superconducting coil means a coil (winding) using a superconductor as a wire.
  • a superconducting coil and a superconducting magnet (sometimes simply called a “magnet” or “magnet”) have substantially the same meaning.
  • a superconducting coil is sometimes simply abbreviated as a "coil.”
  • a superconducting magnet (superconducting coil)
  • the energy stored in the coil is used to prevent the coil from burning out. must be promptly recovered from the coil.
  • the superconducting magnet operated in the drive mode is equipped with a protective resistor (see numeral 25 shown in FIGS. 1 and 2) that converts this energy into heat and recovers it.
  • superconducting magnets that use the low-temperature superconductor LTS as a wire
  • the superconducting coils actively or passively enter a resistance state, and part of the stored energy is used to increase the temperature of the coils. It will bring.
  • the quench margin is small, so when quench buds occur, the resistance region quickly expands, and the stored energy is converted into heat due to the electrical resistance. That is, in the chamber of the cryostat (see reference numeral 18 shown in FIGS. 1 and 2), a shunt resistor/diode is provided in parallel with the superconducting coil. The energy stored in the superconducting coil is distributed and recovered between the electrical resistance inside the coil and these shunt resistors or diodes. Furthermore, in a coil that has a large amount of stored energy, the resistance area is actively expanded using a heater or the like to recover energy in a wide resistance area and prevent burnout of the coil.
  • HTS magnets have a large quench margin, so even if quench occurs, the expansion speed of the resistance region is about two orders of magnitude slower than that of LTS magnets, and resistance generation is limited to a small region. Therefore, the energy stored in the coil is consumed in this small area, which may easily lead to burnout.
  • HTS magnets it is also possible to expand the resistance range using a heater, just as with LTS magnets.
  • HTS magnets have a problem in that they require more thermal energy input than LTS magnets.
  • energy recovery during quenching of the HTS magnet mainly involves external energy recovery, and requires an energy recovery mechanism by turning off the persistent current switch PCS at high speed and by shutting off the power.
  • the persistent current switch PCS is also made of the high temperature superconductor HTS.
  • the persistent current switch PCS (see reference numeral 53 in the comparative example shown in FIG. 2) is generally equipped with a heater (see reference numeral 57 in the comparative example shown in FIG. 2).
  • the persistent current switch PCS itself is put into a resistance state (switched off) by heating it with a heater.
  • a large amount of thermal energy is required to bring the persistent current switch PCS made of the high-temperature superconductor HTS into a resistance state.
  • the present invention provides an excitation power source 23 (referred to as "current source I") for exciting a superconducting coil 11 made of a high-temperature superconductor HTS as a wire, as shown in FIG. ), to which the superconducting coil 11 is connected, and at both ends of the superconducting coil 11, there is a superconducting bypass made of a high-temperature superconductor HTS, which exhibits a sufficiently smaller current capacity than the rated operating current of the superconducting coil 11, as a wire.
  • An embodiment of a superconducting magnet device 10 configured by superconductingly connecting elements 15 will be disclosed. According to the superconducting magnet device 10 according to the present invention, by operating the device 10 in the drive mode, a temporally stable magnetic field can be obtained at low cost while protecting the magnet during quenching.
  • FIG. 1 is a circuit diagram showing the basic configuration of a superconducting magnet device 10 according to an embodiment of the present invention.
  • conductive wires and the like containing a superconductor as a wire are illustrated with thick solid lines
  • conductive wires and the like containing a normal conductor as a wire are illustrated with thin solid lines.
  • a "superconductor” is a substance whose electrical resistance becomes substantially zero below the superconducting critical temperature (which causes a superconducting phenomenon).
  • a superconducting magnet device 10 connects a superconducting bypass element (a "switch element") to a superconducting coil 11 via a first conducting wire 13 made of a superconductor (preferably a high-temperature superconductor HTS). ) 15 connected to the superconducting circuit 16; ) 23 and a protective resistor 25.
  • a superconducting bypass element a "switch element”
  • HTS high-temperature superconductor
  • a magnetic field is generated in the superconducting coil 11 by receiving current from the excitation power source 23 connected in series via the first conducting wire 13 and the power lead 17.
  • the superconducting coil 11 is a coil made of a high-temperature superconductor HTS as a wire material.
  • the high temperature superconductor HTS used in the superconducting coil 11 is not particularly limited, but for example, magnesium diboride (MgB 2 ) can be used.
  • MgB 2 magnesium diboride
  • the superconducting coil 11 is connected in series to an excitation power source 23 via a first conducting wire 13 and a pair of power leads 17a, 17b, etc., respectively.
  • the pair of power leads 17a and 17b may be collectively referred to as "power leads 17."
  • a superconducting bypass element 15 is connected to both ends of the superconducting coil 11 via a first conducting wire 13 in a superconducting manner or with a sufficiently low resistance.
  • “superconductingly connected” means, in addition to pressure welding or spot welding, connecting superconductors to each other via superconducting solder or a superconducting phase.
  • the superconducting bypass element 15 is made of a high-temperature superconductor HTS having a sufficiently small (1% or less) current capacity with respect to the rated operating current of the superconducting coil 11.
  • the high temperature superconductor HTS used in the superconducting bypass element 15 is not particularly limited, but for example, magnesium diboride (MgB 2 ) can be suitably employed.
  • the superconducting bypass element 15 suppresses current inflow into the superconducting coil 11 by bypassing a fluctuating current (noise current) that is smaller than the current capacity of the element 15 with respect to the fluctuating component of the current supplied from the excitation power source 23. On the other hand, it has a function of flowing a current exceeding the current capacity to the superconducting coil 11.
  • the superconducting coil 11 short-circuited by the superconducting bypass element 15 does not operate the persistent current switch PCS (see reference numeral 53 in the comparative example shown in FIG. 2 described later) normally used in persistent current mode operation. (without providing the heater 57 in the persistent current switch PCS53), excitation and demagnetization can be performed.
  • the superconducting magnet device 10 according to the embodiment of the present invention although the superconducting coil 11 behaves like a normal electromagnet, it is possible to achieve magnetic field stability equivalent to persistent current mode operation.
  • the superconducting first conducting wire 13 and the normally conducting power lead 17 are connected in a normal conducting manner by a joining means such as soldering.
  • the normally conductive power lead 17 and the normally conductive second conducting wire 19 are connected to each other by a joining means such as soldering.
  • a protective resistor 25 is connected in parallel to the superconducting circuit 16 including the superconducting coil 11 via the first conducting wire 13 and the power lead 17.
  • the protective resistor 25 plays the role of recovering the energy accumulated in the superconducting coil 11 during quenching.
  • the excitation power source 23 plays a role of supplying DC excitation current to the superconducting coil 11 via the second conductive wire 19, the power lead 17, and the first conductive wire 13, respectively.
  • the excitation current supplied by the excitation power supply 23 is variably set to an appropriate magnitude.
  • a pair of circuit breakers 21a and 21b are inserted and connected to both ends of the excitation power source 23 of the second conducting wire 19.
  • the pair of circuit breakers 21a and 21b serve to disconnect the excitation power source 23 from the superconducting circuit 16 including the superconducting coil 11 during quenching.
  • the superconducting bypass element 15 having a smaller current capacity than the rated operating current of the superconducting coil 11 is connected to both ends of the superconducting coil 11 in a superconducting manner, and the superconducting coil 11 is An excitation power source 23 for excitation is connected to the superconducting coil 11 for operation. That is, the superconducting bypass element 15 and the protective resistor 25 are connected to the superconducting coil 11 in parallel.
  • the superconducting bypass element 15 which is a switch element, is configured using a high-temperature superconductor HTS as a wire, and the current capacity of the superconducting bypass element 15 is sufficiently smaller than the rated operating current of the superconducting coil 11.
  • the superconducting bypass element 15 electrically short-circuits the superconducting coil 11 in a low resistance state (switch-on state) while generating a predetermined magnetic field. , when changing the magnetic field, it enters a high resistance state (switched off state), and changes the open/close state spontaneously (passively) by changing the amount of current supplied from the excitation power supply 23 to the superconducting coil 11. It works like this.
  • the open/close state of the superconducting bypass element 15 can be spontaneously (passively) changed by changing the amount of current supplied from the excitation power source 23 to the superconducting coil 11. Since the superconducting coil 11 is excited/demagnetized only by turning on/off current from the excitation power source 23, a temporally stable magnetic field can be realized in drive mode operation.
  • FIG. 2 is a circuit diagram showing the basic configuration of a superconducting magnet device 50 according to a comparative example.
  • conductive wires made of a superconductor are shown as thick solid lines
  • conductive wires made of a normal conductor are shown as thin solid lines.
  • the superconducting magnet device 10 according to the embodiment of the present invention and the superconducting magnet device 50 according to the comparative example have similar basic configurations. Therefore, the description will focus on the differences between the two, instead of the description of the basic configuration of the superconducting magnet device 50 according to the comparative example.
  • the superconducting circuit 52 is made of a superconductor (not the high-temperature superconductor HTS), as shown in FIG.
  • a persistent current switch PCS 53 is connected in parallel to the superconducting coil 51 via the first conducting wire 13.
  • the persistent current switch PCS 53 belonging to the superconducting circuit 52 includes a superconducting wire 55 made of a superconductor (not a high-temperature superconductor HTS) and a heater 57 for heating the superconducting wire 55. It consists of: Heater 57 is provided close to superconducting wire 55 . A heater power source 59 is connected to the heater 57 .
  • a superconducting circuit 52 provided in a superconducting magnet device 50 receives a current supply from an excitation power source 23 connected in series via a first conductive wire 13 and a power lead 17, and includes a superconducting coil 51 and a superconducting conductive wire 55. A predetermined persistent current is circulated within the superconducting circuit 52. Thereby, the superconducting circuit 52 generates a magnetic field in the superconducting coil 51.
  • the superconducting wire 55 when the superconducting wire 55 is heated by the heater 57 and the temperature of the superconducting wire 55 exceeds a predetermined superconducting critical temperature, the superconducting wire 55 changes from the superconducting state to the normal state. It transitions to a conductive state (that is, the persistent current switch PCS53 turns off). Thereafter, when the heating by the heater 57 is stopped and the superconducting wire 55 is cooled down to below the superconducting critical temperature, the superconducting wire 55 transitions to a superconducting state (that is, the persistent current switch PCS 53 is turned on).
  • FIG. 3 is a conceptual diagram showing the basic mounting state of the superconducting magnet device 10 according to the embodiment of the present invention.
  • the superconducting circuit 16 included in the superconducting magnet device 10 according to the embodiment of the present invention is housed in a cryostat 18, which is an insulated vacuum container.
  • the cryostat 18 is configured to cool the indoor temperature of the cryostat 18 to below a predetermined superconducting critical temperature using an electric refrigerator (see reference numeral 31 in FIG. 9), liquid helium, nitrogen, hydrogen, argon, etc. There is.
  • the cryostat 18 has a pair of through holes 20 for inserting the power lead 17 therethrough.
  • a pair of power leads 17 connected to the superconducting circuit 16 are fixed to the cryostat 18 while being inserted through the pair of through holes 20 .
  • the side of the power lead 17 connected to the excitation power source 23 is exposed to the outside of the cryostat 18 .
  • FIG. 4 is an equivalent circuit diagram for explaining the principle of magnetic field stabilization realized by the superconducting magnet device 10 according to the embodiment of the present invention.
  • the problem here is the DC component (drift). This can be considered as part of periodic noise that fluctuates with an extremely long time constant. Regarding this as well, the cutoff frequency fc may be appropriately set by considering that the period varies in a 24-hour period, for example. However, this concept requires a resistance R of extremely small value. Therefore, consider the DC component as follows. That is, in the equivalent circuit shown in FIG. 4, the time change I(t) of the current supplied from the current source I is considered as shown in (Equation 1).
  • I0 is the set current value
  • a is the amount of variation per unit time.
  • the relationship between the current IL flowing in the coil (superconducting coil 11) and the current IR flowing in the resistor (superconducting bypass element 15) can be described as (Equation 2).
  • the stability of the magnetic field is required to be 0.1 ppm in one hour of magnetic field use, and the inductance L of the superconducting coil 11 is 96H, then The resistance value that satisfies this requirement is 5.3 microohms or less.
  • the time constant ⁇ at this time is about 5000 hours, the cutoff frequency is 8.8 nHz, and the 10 Hz current noise is reduced by about 9 orders of magnitude. In this way, it has been found that by short-circuiting the superconducting coil 11 with a microohm-order resistance (superconducting bypass element 15), stabilization of the magnetic field can be achieved.
  • the superconducting bypass element 15 needs to be turned off when applying current to the coil (superconducting coil 11) or drawing current from the coil, but turned on when generating and using a constant magnetic field.
  • implementation can be considered in which the superconducting bypass element 15 is turned on and off by providing a heater 57 close to the superconducting bypass element 15, like the persistent current switch PCS53 (see FIG. 2) according to the comparative example.
  • PCS53 persistent current switch
  • a wire made of a high-temperature superconductor HTS having a sufficiently small critical current characteristic (for example, 1%) with respect to the rated operating current of the coil (superconducting coil 11) is used to conduct superconducting.
  • a sufficiently small critical current characteristic for example, 1%) with respect to the rated operating current of the coil (superconducting coil 11)
  • the superconducting bypass element 15 spontaneously (passively) performs superconducting without actively driving the heater 57 like the persistent current switch PCS53 according to the comparative example. By making the transition to normal conductivity, a switching operation related to on/off control can be realized.
  • FIG. 5 shows a schematic diagram of the time change in the supply current from the current source I and the time change in magnetic field generation (coil current) during the excitation process.
  • the solid line in FIG. 5 represents the time change in the current supplied from the current source I, and the broken line represents the time change in the generated magnetic field (coil current).
  • the current flowing through the superconducting bypass element 15 has not reached the critical current value, the element 15 maintains its superconducting state, and no current flows through the coil (superconducting coil 11) for a while. It does not flow (see the section from time t0 to time t51 shown in FIG. 5).
  • FIG. 6 shows a schematic diagram of the time change in the current supplied from the current source I and the time change in magnetic field generation (coil current) during the demagnetization process.
  • the solid line in FIG. 6 represents the time change of the supplied current from the current source I, and the broken line represents the time change of the generated magnetic field (coil current).
  • the supply current value of the current source I is gradually decreased linearly from the point where the current source I is operated at a constant value (see the section before time t61 shown in FIG. 6) (see the section after time t61 shown in FIG. 6). From the coil and the superconducting bypass element 15, it appears that a current in the opposite direction from the current source I is superimposed and swept, and the same phenomenon as in the excitation process occurs regarding this reverse direction current.
  • the current supply from the current source I can be performed without being conscious of turning on/off the heater 57 or adjusting the current. It becomes possible to excite and demagnetize the magnet (superconducting coil 11) only by manipulating the amount.
  • Sufficient energy (calorific value) is required to completely bring the superconducting bypass element 15 into a normal conducting state using Joule heat, and this is due to the normal conducting resistance of the high temperature superconductor HTS that constitutes the superconducting bypass element 15 and the superconducting bypass element. It is determined by Joule heat generation, which is determined by the square product of the current flowing through 15, and the heat generation duration time.
  • the current is suddenly increased to instantly increase the heat generation of the superconducting bypass element 15 (pre-energization operation:
  • the time delay can be shortened. Therefore, by designing and controlling the current sweep speed and current input amount in the pre-energization before the start of the current sweep, the time required to transition the superconducting bypass element 15 to the resistance state and the current input speed to the coil can be controlled. be able to.
  • the current capacity of the superconducting bypass element 15 is sufficient as long as it can pass the ripple noise current of the current source I, and if the current capacity is too large, a large current is required to bring the superconducting bypass element 15 into a voltage generating state. It becomes wasted. Therefore, the current capacity of the superconducting bypass element 15 is approximately less than 1% of the rated operating current of the superconducting coil 11, and the current is approximately less than 1 A.
  • the superconducting bypass element 15 When the superconducting bypass element 15 is in a resistance state (switch-off state), the accumulated energy of the superconducting coil 11 is distributed to the protective resistor 25 and the normal resistance (electrical resistance in the switch-off state) of the superconducting bypass element 15 in inverse proportion to each other. and recovered as heat.
  • the normal resistance of the superconducting bypass element 15 is not sufficiently large with respect to the protective resistor 25, the energy of the magnet is recovered inside the cryostat 18 in which the superconducting bypass element 15 is provided, so that recooling takes time. Further, a heat capacity is required to prevent the superconducting bypass element 15 itself from being burnt out.
  • the value of the electrical resistance of the superconducting bypass element 15 in the switch-off state is set to a value that is 10 times or more, preferably 30 times or more, as compared to the value of the electrical resistance of the protective resistor 25.
  • the superconducting bypass element 15 was designed so that the electrical resistance value in the switch-off state was 100-300 ohms.
  • the superconducting coil 11 was manufactured by winding 85 m of a magnesium diboride (MgB 2 ) superconducting single core wire with a wire diameter of 0.64 mm and having a base material of niobium titanium alloy (Nb-Ti).
  • the superconducting bypass element 15 was also manufactured using the magnesium diboride (MgB 2 ) superconducting single core wire.
  • the resistivity of this superconducting single core wire at 40K is designed to be 38 x 10 ⁇ -8 ohm meters, and the electrical resistance value at this time is 100 ohms.
  • the critical current value is defined as the current when an electric field of 1 ⁇ 10 ⁇ -4 [V/m] is generated.
  • the wire length of the superconducting coil 11 is 85 m
  • the voltage generated in the superconducting bypass element 15 when a current corresponding to the critical current value flows through the element 15 is 8.5 mV.
  • the superconducting coil 11 is excited by the voltage (8.5 mV) generated in the superconducting bypass element 15.
  • the inductance of the superconducting coil 11 is 96H, the rate of increase in the current applied to the superconducting coil 11 by this voltage is 89 ⁇ A/sec. Under these conditions, it would take as much as 780 hours to excite the magnet to the rated operating current (250 A), which is not realistic.
  • the current capacity of the superconducting bypass element 15 only needs to have a capacity for transmitting current noise, and as mentioned above, it is desirable to have a small current capacity from the viewpoint of voltage generation. Therefore, the current capacity of the superconducting bypass element 15 is approximately 1% or less (or 1 A or less) with respect to the rated operating current of the superconducting coil 11.
  • HTS copper oxide superconductor
  • BSCCO bismuth-based superconductor
  • MgB 2 magnesium diboride
  • the superconducting bypass element 15 is provided at a location that belongs to a temperature range higher than the rated operating temperature of the superconducting coil 11.
  • the temperature range related to this temperature region is set below the critical temperature of the superconducting bypass element 15 and within 5K with respect to the critical temperature. In this way, by providing the superconducting bypass element 15 at a location that belongs to a temperature range higher than the rated operating temperature of the superconducting coil 11 and operating the superconducting bypass element 15 near the critical temperature, the rated operating temperature of the superconducting coil 11 can be achieved.
  • a superconducting bypass element 15 having a current capacity on the order of 1% of current is realized.
  • the superconducting bypass element 15 by installing the superconducting bypass element 15 in a relatively high-temperature atmosphere environment, it can be transferred to the normal conductive state even with a slight Joule heat generation, so that the superconducting bypass element 15 can easily be placed in the resistance state (switched off state). ).
  • the inductance is often reduced to zero by using non-inductive winding, but in the embodiment according to the present invention, the superconducting bypass element 15 is inductively wound. By doing so, the current transport characteristics are reduced by the self-magnetic field generated in the superconducting bypass element 15 during excitation and demagnetization.
  • the ambient temperature at the location where the superconducting bypass element 15 is installed is set to be just below the critical temperature of the superconductor. Near the critical temperature, it becomes sensitive to magnetic fields, making it possible to more effectively reduce the current capacity. As a result, a superconducting bypass element 15 with good controllability can be realized.
  • the inductively wound superconducting bypass element 15 has an inductance, and the noise current is distributed between the superconducting coil 11 and the superconducting bypass element 15 with an inverse ratio of impedance between the superconducting coil 11 and the superconducting bypass element 15. become.
  • the inductance of the superconducting coil 11 is on the order of 100H, and by configuring the inductance of the superconducting bypass element 15 on the order of 1 mH, the incorporation of ripple noise can be reduced to approximately one hundred thousandth. Ripple noise is sufficiently small compared to 1 ⁇ 10 ⁇ -3.
  • the superconducting bypass element 15 is inductively wound on the order of 1 mH, the magnetic field fluctuation due to ripple noise can be suppressed to the order of 1 ⁇ 10 ⁇ -7, so that no practical problem occurs in MRI applications, for example.
  • FIG. 9 is a conceptual diagram showing a first mounting state of the superconducting magnet device 10 according to the embodiment of the present invention.
  • illustrations of the excitation power source 23, protection resistor 25, etc. connected to the power lead 17 are omitted (because they are similar to the example shown in FIG. 3).
  • the superconducting magnet device 10 employing this first mounting state is a conduction-cooled superconducting magnet device for tunnel-type MRI that generates a horizontal magnetic field.
  • the superconducting magnet device 10 is equipped with an electric refrigerator 31.
  • the electric refrigerator 31 for example, a Gifford-McMahon refrigerator (GM refrigerator), which is a two-stage refrigerator, can be employed.
  • GM refrigerator Gifford-McMahon refrigerator
  • This electric refrigerator (GM refrigerator) 31 has a two-stage cooling capacity, and the first stage (the first stage 33 related to the electric refrigerator 31) can cool down to 80K or less, and the second stage (Second stage 35 related to electric refrigerator 31) can cool to a range of about 4-10K.
  • the superconducting circuit 16 provided in the superconducting magnet device 10 is operated in a state where it is conductively cooled by the action of the electric refrigerator 31.
  • the superconducting coil 11, superconducting bypass element 15, etc. provided in the superconducting circuit 16 are provided inside the cryostat 18, as in the example shown in FIG.
  • the superconducting first conducting wire 13 related to the superconducting circuit 16 is connected via the HTS power lead 22. It is connected to a power lead 17 that is normally conductive (for example, made of phosphorus-deoxidized copper).
  • the high temperature superconducting HTS power lead 22 is made of a copper oxide superconductor such as REBCO or BSCCO.
  • the connection part 24 (see FIG. 9) between the normal conductive power lead 17 and the high temperature superconducting HTS power lead 22 is thermally anchored to the first stage 33 of the electric refrigerator 31 (see FIG. 9). (see dashed arrow). Furthermore, the low temperature section 26 of the HTS power lead 22 is thermally anchored to the second stage 35 of the electric refrigerator 31 (see the broken line arrow in FIG. 9).
  • an 80K radiation shield is provided inside the cryostat 18 so as to enclose the cryogenic part including the superconducting circuit 16.
  • This radiation shield is attached to the first stage 33 of the electric refrigerator 31.
  • the radiation shield serves to protect the interior of the radiation shield from radiant heat outside the cryostat 18 by keeping it in a cooled state.
  • the superconducting coil 11 and the superconducting bypass element 15 are superconductingly connected to form a superconducting loop via the first conducting wire 13 made of the above-described magnesium diboride (MgB 2 ) superconducting single-core wire. There is.
  • the superconducting coil 11 and the first conducting wire 13 are attached to the second stage 35 of the electric refrigerator 31 using a metal mounting member (non-metallic mounting member) having high thermal conductivity. (see dashed line arrow in FIG. 9). As a result, the superconducting coil 11 and the first conducting wire 13 are conductively cooled.
  • the first conducting wire 13 supplies current to the superconducting loop configured including the superconducting coil 11 and the superconducting bypass element 15, and The low temperature section 26 of the HTS power lead 22 and the superconducting loop are electrically connected.
  • a mounting member 37 made of stainless steel is provided for producing the same.
  • the superconducting bypass element 15 is provided in a thermally coupled state to this mounting member 37.
  • the mounting member 37 is connected integrally to each of the first stage 33 and the second stage 35 of the electric refrigerator 31, but the mounting member 37 is a separate thermal link.
  • Each of the first stage 33 and second stage 35 of the electric refrigerator 31 may be thermally coupled to the mounting member 37 via.
  • FIGS. 10A and 10B are conceptual diagrams showing examples of operating temperature settings for the superconducting bypass element 15.
  • the relationship between the temperature difference and heat flow between two points is equivalent to the relationship between potential difference and current. Therefore, as shown in FIGS. 10A and 10B, the temperature difference between the first stage temperature TH of the electric refrigerator 31 and the second stage temperature TL of the electric refrigerator 31 is distributed using thermal resistance. By doing so, the desired intermediate temperature Tm is achieved. Thermal conductivity exhibits nonlinearity with respect to temperature. Generally, the higher the temperature, the higher the thermal conductivity and the lower the thermal resistance.
  • the intermediate temperature Tm moves toward the first stage temperature TH compared to when there is no heat generation.
  • the effect of reducing the dynamic current capacity can be obtained by current shunting during excitation and demagnetization.
  • the heat transfer paths (first heat transfer path and An intermediate temperature Tm based on the temperature difference between the first stage temperature TH and the second stage temperature TL is set by the thermal resistance in the second heat transfer path (second heat transfer path).
  • the thermal resistance related to the first heat transfer path from the installation location of the electric refrigerator 31 to the first stage 33, and the second heat transfer path from the installation location of the electric refrigerator 31 to the second stage 35 is set by the interaction with the thermal resistance.
  • the temperature dependence of thermal resistance differs depending on the type of material. Therefore, it is preferable to set the thermal conductivity to be different between the first heat transfer path and the second heat transfer path.
  • the intermediate temperature Tm can be brought closer to the first stage temperature TH.
  • FIG. 11 is a conceptual diagram showing a second mounting state of the superconducting magnet device 10 according to the embodiment of the present invention.
  • the first mounting state of the superconducting magnet device 10 shown in FIG. 9 and the second mounting state of the superconducting magnet device 10 shown in FIG. 11 have many common parts. Therefore, the differences between the two will be explained in place of the explanation of the second mounting state of the superconducting magnet device 10.
  • the superconducting circuit 16 provided in the superconducting magnet device 10 according to the second mounting state is kept at an extremely low temperature while being enclosed within the refrigerant container 41 containing the liquid refrigerant. is maintained. That is, the superconducting circuit 16 provided in the superconducting magnet device 10 is immersed and cooled with a liquid refrigerant. Note that a part or all of the winding portion of the superconducting coil 11 is directly cooled by the liquid refrigerant. Moreover, the superconducting bypass element 15 is located exposed from the liquid surface of the liquid refrigerant.
  • the superconducting bypass element 15 is thermally coupled to a portion of the refrigerant container 41 existing in the radiation shield 43 room that exhibits a higher temperature than the internal space average temperature.
  • the thermal resistance of the first heat transfer path from the superconducting bypass element 15 to the above-described high temperature portion and the gap between the superconducting bypass element 15 and the superconducting coil 11 The operating temperature of the superconducting bypass element 15 is set based on the thermal resistance of the first conducting wire 13 that electrically connects the superconducting bypass element 15 and the corresponding resistance ratio.
  • FIG. 12 is a conceptual diagram showing a third mounting state of the superconducting magnet device 10 according to the embodiment of the present invention.
  • the second mounting state of the superconducting magnet device 10 shown in FIG. 11 and the third mounting state of the superconducting magnet device 10 shown in FIG. 12 have many common parts. Therefore, the differences between these two will be explained in place of the explanation of the third mounting state of the superconducting magnet device 10.
  • a cooling system that directly cools the superconducting coil 11 using a refrigerant is used as a cooling means
  • the second mounting state of the superconducting magnet device 10 shown in FIG. The three mounting states are the same in that they use a refrigerant as a cooling means, but they are different in that they employ a cooling system that indirectly cools the superconducting coil 11 using a refrigerant.
  • the operating temperature of the superconducting bypass element 15 is set to The temperature is set higher than the ambient temperature related to the coil 11.
  • the heat transfer path from the high-temperature portion to the superconducting bypass element 15 is not limited to a heat transfer path using physical solid-state heat conduction.
  • it may be a heat transfer path using heat transfer by gas such as helium gas, or it may be a heat transfer path using radiation.
  • the current capacity of the superconducting bypass element 15 can be made sufficiently smaller than the current capacity of the superconducting coil 11.
  • FIG. 13 is an explanatory diagram showing a nuclear magnetic resonance diagnostic apparatus 71 using the superconducting magnet device 10 according to the embodiment of the present invention.
  • the nuclear magnetic resonance diagnostic device 70 using the superconducting magnet device 10 according to the embodiment of the present invention is a device that utilizes the nuclear magnetic resonance phenomenon to visualize the internal state of a living body and provide it for diagnosis.
  • the nuclear magnetic resonance diagnostic apparatus 70 includes a bed 73 on which a subject 71 lies in a gap between a superconducting magnet device 10 that includes an upper superconducting coil 11 and a lower superconducting coil 11. is configured to be transported by a transporter 75 so as to be able to move forward and backward.
  • the nuclear magnetic resonance diagnostic apparatus 70 using the superconducting magnet device 10 according to the embodiment of the present invention, the internal state of the living body of the subject M can be visualized and used for diagnosis.
  • the nuclear magnetic resonance diagnostic apparatus 70 has been described as an example of application of the superconducting magnet device 10 according to the embodiment of the present invention, the present invention is not limited to this example.
  • the superconducting magnet device 10 according to the embodiment of the present invention can be applied to any application requiring a temporally stable magnetic field.

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Abstract

A superconducting magnet device (10) is equipped with a superconducting coil (11) and an excitation power supply (23) for exciting the superconducting coil (11). A protective resistor (25) and a superconducting bias element (15) which has a high-temperature superconductor as a wire material are connected in parallel to the superconducting coil (11). The current capacity of the superconducting bias element (15) is sufficiently less than the rated operation current of the superconducting coil (11). The superconducting bias element (15) electrically shorts the superconducting coil (11) in a low-resistance state when a prescribed magnetic field is created, and when the magnetic field changes, performs an operation for spontaneously changing the switching state by changing to a high-resistance state and changing the current supply amount from the excitation power supply (23) to the superconducting coil (11).

Description

超電導磁石装置、及び核磁気共鳴診断装置Superconducting magnet device and nuclear magnetic resonance diagnostic device
　本発明は、高い磁場を発生させその磁場を利用する超電導磁石装置、及び核磁気共鳴診断装置に関する。 The present invention relates to a superconducting magnet device that generates a high magnetic field and utilizes the magnetic field, and a nuclear magnetic resonance diagnostic device.
　超電導磁石装置は、永久磁石や常電導電磁石に比べて高い磁場を発生させることができる。そのため、超電導磁石装置は、研究用超高磁場マグネットやＮＭＲ（nuclear magnetic resonance：核磁気共鳴）のような分析装置のマグネット、医療ＭＲＩ（Magnetic Resonance Imaging：磁気共鳴イメージング）のマグネットとして汎用されている。 A superconducting magnet device can generate a higher magnetic field than permanent magnets or normal conducting electromagnets. For this reason, superconducting magnet devices are widely used as ultra-high magnetic field magnets for research, magnets for analysis devices such as NMR (nuclear magnetic resonance), and magnets for medical MRI (Magnetic Resonance Imaging). .
　超電導磁石装置の運転モードは大きく２つに分類される（例えば特許文献１参照）。
　第１の運転モードは、電源から電流を供給して磁石を励磁することで磁場を発生させ、運転中は電源から電流を流したままとする電源駆動モード（ドライブモード）である。 The operating modes of superconducting magnet devices are broadly classified into two (see, for example, Patent Document 1).
The first operation mode is a power drive mode in which a magnetic field is generated by supplying current from the power supply to excite the magnet, and the current continues to flow from the power supply during operation.
　第２の運転モードは、超電導磁石に永久電流スイッチPCS (persistent current switch)を設けて超電導回路を構成し、同超電導回路に電源から電流を投入して磁場を発生させ、その後に電源の電流供給を断ち、超電導回路に流れ続ける超電導電流によって磁場を維持する永久電流モードである。 In the second operation mode, a superconducting circuit is constructed by installing a persistent current switch (PCS) in the superconducting magnet, a current is applied to the superconducting circuit from the power source to generate a magnetic field, and then the current is supplied from the power source. This is a persistent current mode in which the magnetic field is maintained by the superconducting current that continues to flow through the superconducting circuit.
　電源から切り離された状態で運転する永久電流モードでは、電源からのノイズの侵入がないため、時間的に安定な磁場が得られる。この性質を利用して特に磁場の安定度が必要となるＮＭＲやＭＲＩの用途において、既存の常識では、永久電流モードでの運転が必須であると考えられていた。 In persistent current mode, which operates while disconnected from the power supply, there is no noise intrusion from the power supply, so a temporally stable magnetic field can be obtained. In applications such as NMR and MRI that utilize this property and particularly require stability of the magnetic field, conventional wisdom has believed that operation in persistent current mode is essential.
特開２０１８－１６４０２８号公報JP2018-164028A
　ところが、超電導磁石装置を永久電流モードで運転すると、以下のような不具合が生じる。すなわち、永久電流スイッチPCSに大電流を流すためには、永久電流スイッチPCSが有する超電導導線の断面積を大きくする（つまり、超電導導線の径を太くする）ことを要する。
　また、超電導導線をヒータで加熱して常電導転移させて必要な抵抗を発生させるためには、超電導導線の長さを充分に確保することを要する。 However, when a superconducting magnet device is operated in persistent current mode, the following problems occur. That is, in order to cause a large current to flow through the persistent current switch PCS, it is necessary to increase the cross-sectional area of the superconducting wire included in the persistent current switch PCS (that is, increase the diameter of the superconducting wire).
Furthermore, in order to heat the superconducting wire with a heater to cause it to transition to normal conductivity and generate the necessary resistance, it is necessary to ensure a sufficient length of the superconducting wire.
　本発明は、上記実情に鑑みてなされたものであり、時間的に安定な磁場をドライブモード運転で実現可能な超電導磁石装置、及び核磁気共鳴診断装置を提供することを課題とする。 The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a superconducting magnet device and a nuclear magnetic resonance diagnostic device that can realize a temporally stable magnetic field in drive mode operation.
発明を解決するための手段means to solve the invention
　前記課題を解決するために、本発明に係る超電導磁石装置は、超電導線材が巻き回された超電導コイルと、該超電導コイルを励磁するための電源と、を備える超電導磁石装置であって、前記超電導コイルには、スイッチ素子及び保護抵抗が並列に接続され、前記スイッチ素子は、高温超電導体を線材として構成されており、当該スイッチ素子の電流容量は、前記超電導コイルに係る定格運転電流と比べて十分に小さく、当該スイッチ素子は、所定の磁場を発生している際には、低抵抗状態で前記超電導コイルを電気的に短絡する一方、磁場を変化させている際には、高抵抗状態になり、前記電源から前記超電導コイルへの電流供給量を変更することで自発的に開閉状態を変えるように動作することを最も主要な特徴とする。 In order to solve the above problems, a superconducting magnet device according to the present invention is a superconducting magnet device comprising a superconducting coil around which a superconducting wire is wound, and a power source for exciting the superconducting coil, A switch element and a protective resistor are connected in parallel to the coil, and the switch element is made of a high-temperature superconductor wire, and the current capacity of the switch element is greater than the rated operating current of the superconducting coil. The switching element is sufficiently small and electrically shorts the superconducting coil in a low resistance state when a predetermined magnetic field is being generated, and in a high resistance state when the magnetic field is changing. The main feature is that the superconducting coil operates to spontaneously change its open/close state by changing the amount of current supplied from the power source to the superconducting coil.
　本発明に係る超電導磁石装置によれば、時間的に安定な磁場をドライブモードで実現することができる。 According to the superconducting magnet device according to the present invention, a temporally stable magnetic field can be realized in drive mode.
本発明の実施形態に係る超電導磁石装置の基本構成を表す回路図である。1 is a circuit diagram showing the basic configuration of a superconducting magnet device according to an embodiment of the present invention. 比較例に係る超電導磁石装置の基本構成を表す回路図である。FIG. 2 is a circuit diagram showing the basic configuration of a superconducting magnet device according to a comparative example. 本発明の実施形態に係る超電導磁石装置の基本実装状態を表す概念図である。1 is a conceptual diagram showing a basic mounting state of a superconducting magnet device according to an embodiment of the present invention. 本発明の実施形態に係る超電導磁石装置が実現する磁場安定化を説明するための等価回路図である。FIG. 2 is an equivalent circuit diagram for explaining magnetic field stabilization realized by the superconducting magnet device according to the embodiment of the present invention. 本発明の実施形態に係る超電導磁石装置の励磁過程において、励磁電源及び超電導コイルのそれぞれに流れる電流の時間変化を表す図である。FIG. 3 is a diagram showing temporal changes in currents flowing through each of an excitation power source and a superconducting coil during the excitation process of the superconducting magnet device according to the embodiment of the present invention. 本発明の実施形態に係る超電導磁石装置の減磁過程において、励磁電源及び超電導コイルのそれぞれに流れる電流の時間変化を表す図である。FIG. 2 is a diagram showing temporal changes in currents flowing through each of an excitation power source and a superconducting coil during a demagnetization process of a superconducting magnet device according to an embodiment of the present invention. 本発明の実施形態に係る超電導磁石装置の電流調整過程において、励磁電源及び超電導コイルのそれぞれに流れる電流の時間変化を表す図である。FIG. 4 is a diagram showing temporal changes in currents flowing through each of an excitation power source and a superconducting coil in a current adjustment process of a superconducting magnet device according to an embodiment of the present invention. 本発明の実施形態に係る超電導磁石装置をプレ通電運転した場合において、励磁電源及び超電導コイルのそれぞれに流れる電流の時間変化を表す図である。FIG. 6 is a diagram showing temporal changes in currents flowing through each of the excitation power source and the superconducting coil when the superconducting magnet device according to the embodiment of the present invention is subjected to pre-energization operation. 本発明の実施形態に係る超電導磁石装置の第１実装状態を表す概念図である。FIG. 1 is a conceptual diagram showing a first mounting state of a superconducting magnet device according to an embodiment of the present invention. 超電導バイパス素子に係る運転温度設定例を表す概念図である。It is a conceptual diagram showing an example of operating temperature setting concerning a superconducting bypass element. 超電導バイパス素子に係る運転温度設定例を表す概念図である。It is a conceptual diagram showing an example of operating temperature setting concerning a superconducting bypass element. 本発明の実施形態に係る超電導磁石装置の第２実装状態を表す概念図である。It is a conceptual diagram showing the 2nd mounting state of the superconducting magnet device concerning an embodiment of the present invention. 本発明の実施形態に係る超電導磁石装置の第３実装状態を表す概念図である。It is a conceptual diagram showing the 3rd mounting state of the superconducting magnet device concerning an embodiment of the present invention. 本発明の実施形態に係る超電導磁石装置を用いた核磁気共鳴診断装置を表す説明図である。FIG. 1 is an explanatory diagram showing a nuclear magnetic resonance diagnostic apparatus using a superconducting magnet device according to an embodiment of the present invention.
　以下、本発明の複数の実施形態について、適宜図面を参照して説明する。
　以下の説明は本発明の実施形態を示すものであり、本発明はこれらの説明に限定されるものではない。本発明を説明するための図面において、同一の機能を有するものには同一の符号を付し、その繰り返しの説明は省略する場合がある。 Hereinafter, a plurality of embodiments of the present invention will be described with reference to the drawings as appropriate.
The following description shows embodiments of the present invention, and the present invention is not limited to these descriptions. In the drawings for explaining the present invention, parts having the same functions are denoted by the same reference numerals, and repeated description thereof may be omitted.
〔前提となる背景技術〕
　本発明に係る超電導磁石装置１０の説明に先立って、前提となる背景技術について概説する。
　従来、実用的な超電導体として金属系のニオブチタン合金（Ｎｂ－Ｔｉ）、ニオブスズ（Ｎｂ３Ｓｎ）が利用されてきた。これらの材料は低温超電導体（LTS：Low Temperature Superconductor）と呼ばれ、液体ヘリウムを利用した極低温の温度領域で利用されている。 [Prerequisite background technology]
Prior to the explanation of the superconducting magnet device 10 according to the present invention, the underlying background technology will be outlined.
Conventionally, metallic niobium titanium alloys (Nb-Ti) and niobium tin (Nb 3 Sn) have been used as practical superconductors. These materials are called low temperature superconductors (LTS) and are used in the extremely low temperature range using liquid helium.
　それに対し、高い臨界温度で超電導特性が発現する高温超電導体（HTS: High Temperature Superconductor）の実用化研究が進んでいる。近年では、様々なHTS磁石が開発されてきている。高温超電導体HTSとしては、レアアース系元素（Y,Gdなど）を含むREBCO、Biを含むBSCCOなどの銅酸化物超電導体や金属系材料の二硼化マグネシウム（ＭｇＢ２）の実用化が進められている。 In response, research is progressing on the practical application of high temperature superconductors (HTS), which exhibit superconducting properties at high critical temperatures. In recent years, various HTS magnets have been developed. As high-temperature superconductors HTS, copper oxide superconductors such as REBCO containing rare earth elements (Y, Gd, etc.) and BSCCO containing Bi, and magnesium diboride (MgB 2 ), a metal material, are being put into practical use. ing.
　高温超電導体HTSは臨界温度が高く、また、その性質を利用して液体ヘリウム温度領域と比べて桁違いに大きな比熱となる温度領域で運転される。そのため、擾乱による超電導磁石への熱エネルギーに入熱による常電導転移現象（クエンチ）に対してLTS磁石と比べて桁違いに大きなクエンチエネルギーマージンを持つ点で、高温超電導磁石（HTS磁石）の実用化が期待されている。 The high-temperature superconductor HTS has a high critical temperature, and by utilizing this property, it is operated in a temperature range where the specific heat is an order of magnitude higher than that of liquid helium. Therefore, high-temperature superconducting magnets (HTS magnets) can be put to practical use in that they have an order of magnitude larger quench energy margin than LTS magnets against the normal conduction transition phenomenon (quench) caused by thermal energy input into the superconducting magnets due to disturbances. It is expected that
　また、近年、高温超電導体HTSにおいても実用的な超電導接続技術が開発され、HTS磁石においても永久電流モード運転が可能となってきている。さらに、核磁気共鳴分光装置ＮＭＲ（nuclear magnetic resonance）向けの磁石の開発もなされている。 In addition, in recent years, practical superconducting connection technology has been developed for high-temperature superconductor HTS, and persistent current mode operation has become possible for HTS magnets as well. Furthermore, magnets for nuclear magnetic resonance spectroscopy (NMR) have also been developed.
　ここで、本明細書で用いる用語について定義する。超電導コイル（図１に示す符号１１参照）とは、超電導体を線材としたコイル（巻線）を意味する。超電導コイルと、超電導磁石（単に「磁石」や「マグネット」と呼ぶ場合がある。）とは、実質的に同義である。超電導コイルを、単に「コイル」と略称する場合がある。 Here, the terms used in this specification will be defined. A superconducting coil (see reference numeral 11 in FIG. 1) means a coil (winding) using a superconductor as a wire. A superconducting coil and a superconducting magnet (sometimes simply called a "magnet" or "magnet") have substantially the same meaning. A superconducting coil is sometimes simply abbreviated as a "coil."
　さて、超電導磁石（超電導コイル）では、なんらかの原因で超電導状態が壊れて電気抵抗を生じる常電導状態に遷移した場合（クエンチ現象）には、コイルの焼損を防止するため、コイルに蓄積されたエネルギーを同コイルから速やかに回収する必要がある。ドライブモード運転の超電導磁石では、このエネルギーを熱に変換して回収する保護抵抗（図１、図２に示す符号２５参照）が備わっている。超電導コイルの異常時に励磁電源を遮断することにより、保護抵抗において磁石のエネルギーが消費される。その結果、超電導コイルの焼損が防止される。 Now, in a superconducting magnet (superconducting coil), if the superconducting state breaks down for some reason and transitions to a normal conducting state that produces electrical resistance (quench phenomenon), the energy stored in the coil is used to prevent the coil from burning out. must be promptly recovered from the coil. The superconducting magnet operated in the drive mode is equipped with a protective resistor (see numeral 25 shown in FIGS. 1 and 2) that converts this energy into heat and recovers it. By cutting off the excitation power supply when an abnormality occurs in the superconducting coil, the energy of the magnet is consumed in the protective resistor. As a result, burnout of the superconducting coil is prevented.
　また、低温超電導体LTSを線材として用いた超電導磁石（超電導コイル）では、このエネルギー回収過程において、能動的に又は受動的に超電導コイルが抵抗状態となり、蓄積エネルギーの一部はコイルの温度上昇をもたらすこととなる。 In addition, in superconducting magnets (superconducting coils) that use the low-temperature superconductor LTS as a wire, during this energy recovery process, the superconducting coils actively or passively enter a resistance state, and part of the stored energy is used to increase the temperature of the coils. It will bring.
　一方、永久電流モード運転の場合も同様に、超電導磁石（超電導コイル）の焼損防止のためにエネルギー回収が必要である。ところが、永久電流モード運転時には、永久電流スイッチPCS（図２に示す比較例の符号５３参照）によって超電導コイル両端が短絡されていること、また、永久電流モード運転では定常運転時には外部からの電流供給が不要であるため、熱侵入源となる電流リードを取り去って運転する。
　そのため、これまで実用化されてきたLTS永久電流モード運転での超電導コイルでは、外部素子を導入してエネルギー回収を行うのは一般的ではない。 On the other hand, in the case of persistent current mode operation, energy recovery is similarly necessary to prevent burnout of the superconducting magnet (superconducting coil). However, during persistent current mode operation, both ends of the superconducting coil are short-circuited by the persistent current switch PCS (see reference numeral 53 in the comparative example shown in Figure 2). Since this is not necessary, the current lead, which is a source of heat intrusion, is removed during operation.
Therefore, in the superconducting coils operating in the LTS persistent current mode that have been put into practical use so far, it is not common to introduce external elements to recover energy.
　LTS磁石ではクエンチマージンが小さいため、クエンチの芽が発生すると速やかに抵抗領域が拡大し、その電気抵抗によって蓄積エネルギーは熱に変換されることになる。すなわち、クライオスタット（図１、図２に示す符号１８参照）の室内には、分流抵抗／ダイオードが超電導コイルに並列に設けられている。超電導コイルの蓄積エネルギーは、コイル内部の電気抵抗とこれらの分流抵抗又はダイオードに分配されて回収される。
　さらに、蓄積エネルギーが大きなコイルでは、ヒータなどにより積極的に抵抗領域を拡大することにより、広い抵抗領域でエネルギーを回収してコイルの焼損を防止することも行われる。 In LTS magnets, the quench margin is small, so when quench buds occur, the resistance region quickly expands, and the stored energy is converted into heat due to the electrical resistance. That is, in the chamber of the cryostat (see reference numeral 18 shown in FIGS. 1 and 2), a shunt resistor/diode is provided in parallel with the superconducting coil. The energy stored in the superconducting coil is distributed and recovered between the electrical resistance inside the coil and these shunt resistors or diodes.
Furthermore, in a coil that has a large amount of stored energy, the resistance area is actively expanded using a heater or the like to recover energy in a wide resistance area and prevent burnout of the coil.
　一方、HTS磁石ではクエンチマージンが大きいことからクエンチが発生しても抵抗領域の拡大速度はLTS磁石と比べて2桁程度遅く、抵抗発生は小さな領域に制限される。そのため、コイルの蓄積エネルギーは、この小さな領域で消費されることとなり、容易に焼損につながるおそれがある。HTS磁石では、LTS磁石同様に、ヒータによる抵抗領域の拡大も可能である。ところが、HTS磁石では、LTS磁石に比べてより多くの熱エネルギーの投入を要するという問題がある。 On the other hand, HTS magnets have a large quench margin, so even if quench occurs, the expansion speed of the resistance region is about two orders of magnitude slower than that of LTS magnets, and resistance generation is limited to a small region. Therefore, the energy stored in the coil is consumed in this small area, which may easily lead to burnout. With HTS magnets, it is also possible to expand the resistance range using a heater, just as with LTS magnets. However, HTS magnets have a problem in that they require more thermal energy input than LTS magnets.
　従って、HTS磁石のクエンチ時のエネルギー回収では、外部のエネルギー回収をメインとし、永久電流スイッチPCSの高速オフと共に、電源遮断によるエネルギー回収機構が必要となる。 Therefore, energy recovery during quenching of the HTS magnet mainly involves external energy recovery, and requires an energy recovery mechanism by turning off the persistent current switch PCS at high speed and by shutting off the power.
　HTS磁石を永久電流モード運転するためには、当然ながら、永久電流スイッチPCSも高温超電導体HTS よりなることが必要である。
　永久電流スイッチPCS（図２に示す比較例の符号５３参照）には、一般にヒータ（図２に示す比較例の符号５７参照）が備え付けられている。永久電流スイッチPCSそれ自体をヒータで加熱することによって抵抗状態（スイッチオフ）とする。
　ところが、HTS磁石と同様に、高温超電導体HTS よりなる永久電流スイッチPCSを抵抗状態にするためには、多くの熱エネルギーの投入を要する。 In order to operate the HTS magnet in persistent current mode, it is of course necessary that the persistent current switch PCS is also made of the high temperature superconductor HTS.
The persistent current switch PCS (see reference numeral 53 in the comparative example shown in FIG. 2) is generally equipped with a heater (see reference numeral 57 in the comparative example shown in FIG. 2). The persistent current switch PCS itself is put into a resistance state (switched off) by heating it with a heater.
However, like the HTS magnet, a large amount of thermal energy is required to bring the persistent current switch PCS made of the high-temperature superconductor HTS into a resistance state.
　超電導磁石（超電導コイル）の焼損を防止するためには、例えば、100msec未満で永久電流スイッチPCSをオフにしてエネルギー回収動作に移行する必要がある。このため、出力の大きなヒータ用の電源を常に待機させておく必要がある。HTS磁石保護の観点では、永久電流モード運転は極めて不利である。 In order to prevent burnout of the superconducting magnet (superconducting coil), it is necessary to turn off the persistent current switch PCS in less than 100 msec and shift to energy recovery operation, for example. Therefore, it is necessary to always keep a power source for the heater with a large output on standby. From the point of view of HTS magnet protection, persistent current mode operation is extremely disadvantageous.
　ところが、既存の常識では、MRIやNMRのような（画質向上のため）安定磁場を要する磁石応用のケースでは、永久電流モード運転が必須と考えられていた。
　また、最近時、極めて高価な超高安定電源を用いたHTS-MRI磁石やHTS-NMR磁石の開発も報告されている。ただし、製品として広く普及させる観点からは、高価な電源を必要とするシステムは現実的ではない。 However, conventional wisdom has held that persistent current mode operation is essential for magnet applications that require a stable magnetic field (to improve image quality), such as MRI and NMR.
Also, recently, the development of HTS-MRI magnets and HTS-NMR magnets using extremely expensive and ultra-highly stable power supplies has been reported. However, from the perspective of widespread use as a product, a system that requires an expensive power source is not realistic.
　前記した前提となる背景技術を踏まえて、本発明は、図１に示すように、高温超電導体HTSを線材としてなる超電導コイル１１を励磁するための励磁電源２３（「電流源Ｉ」と呼ぶ場合がある。）に対し、超電導コイル１１を接続すると共に、超電導コイル１１の両端に、超電導コイル１１に係る定格運転電流と比べて十分に小さい電流容量を呈する高温超電導体HTSを線材としてなる超電導バイパス素子１５を超電導的に接続して構成される超電導磁石装置１０の実施形態について開示する。
　本発明に係る超電導磁石装置１０によれば、同装置１０をドライブモードで運転することにより、クエンチ時の磁石保護を図りながら、時間的に安定な磁場を安価なコストで得ることができる。 Based on the background technology described above, the present invention provides an excitation power source 23 (referred to as "current source I") for exciting a superconducting coil 11 made of a high-temperature superconductor HTS as a wire, as shown in FIG. ), to which the superconducting coil 11 is connected, and at both ends of the superconducting coil 11, there is a superconducting bypass made of a high-temperature superconductor HTS, which exhibits a sufficiently smaller current capacity than the rated operating current of the superconducting coil 11, as a wire. An embodiment of a superconducting magnet device 10 configured by superconductingly connecting elements 15 will be disclosed.
According to the superconducting magnet device 10 according to the present invention, by operating the device 10 in the drive mode, a temporally stable magnetic field can be obtained at low cost while protecting the magnet during quenching.
〔本発明の実施形態に係る超電導磁石装置１０の基本構成〕
　本発明の実施形態に係る超電導磁石装置１０の基本構成について、図１を参照して説明する。
　図１は、本発明の実施形態に係る超電導磁石装置１０の基本構成を表す回路図である。
　なお、図１では、超電導体を線材として含む導線等を太い実線で図示し、常電導体を線材として含む導線等を細い実線で図示している。「超電導体」とは、超電導臨界温度以下において電気抵抗が実質的にゼロになる（超電導現象を起こす）物質である。 [Basic configuration of superconducting magnet device 10 according to embodiment of the present invention]
The basic configuration of a superconducting magnet device 10 according to an embodiment of the present invention will be described with reference to FIG. 1.
FIG. 1 is a circuit diagram showing the basic configuration of a superconducting magnet device 10 according to an embodiment of the present invention.
In FIG. 1, conductive wires and the like containing a superconductor as a wire are illustrated with thick solid lines, and conductive wires and the like containing a normal conductor as a wire are illustrated with thin solid lines. A "superconductor" is a substance whose electrical resistance becomes substantially zero below the superconducting critical temperature (which causes a superconducting phenomenon).
　本発明の実施形態に係る超電導磁石装置１０は、超電導コイル１１に対し、超電導体（好ましくは高温超電導体HTS）を線材としてなる第１導線１３を介して、超電導バイパス素子（「スイッチ素子」に相当する。）１５を接続してなる超電導回路１６と、超電導回路１６に対し、パワーリード１７及び常電導体を線材としてなる第２導線１９をそれぞれ介して接続される励磁電源（「電源」に相当する。）２３並びに保護抵抗２５と、を備える。 A superconducting magnet device 10 according to an embodiment of the present invention connects a superconducting bypass element (a "switch element") to a superconducting coil 11 via a first conducting wire 13 made of a superconductor (preferably a high-temperature superconductor HTS). ) 15 connected to the superconducting circuit 16; ) 23 and a protective resistor 25.
　超電導回路１６では、第１導線１３及びパワーリード１７を介して直列接続された励磁電源２３からの電流供給を受けて、超電導コイル１１において磁場を発生させる。 In the superconducting circuit 16, a magnetic field is generated in the superconducting coil 11 by receiving current from the excitation power source 23 connected in series via the first conducting wire 13 and the power lead 17.
　超電導コイル１１は、高温超電導体HTSを線材としてなるコイルである。超電導コイル１１に用いられる高温超電導体HTSとしては、特に限定されないが、例えば、二硼化マグネシウム（ＭｇＢ２）を採用することができる。超電導コイル１１は、図１に示すように、第１導線１３及び一対のパワーリード１７ａ、１７ｂ等をそれぞれ介して励磁電源２３に直列接続されている。ただし、本明細書、図面において、一対のパワーリード１７ａ、１７ｂを「パワーリード１７」と総称する場合があることを付言しておく。 The superconducting coil 11 is a coil made of a high-temperature superconductor HTS as a wire material. The high temperature superconductor HTS used in the superconducting coil 11 is not particularly limited, but for example, magnesium diboride (MgB 2 ) can be used. As shown in FIG. 1, the superconducting coil 11 is connected in series to an excitation power source 23 via a first conducting wire 13 and a pair of power leads 17a, 17b, etc., respectively. However, it should be noted that in this specification and the drawings, the pair of power leads 17a and 17b may be collectively referred to as "power leads 17."
　超電導コイル１１の両端には、第１導線１３を介して、超電導バイパス素子１５が超電導的に、又は、十分に低抵抗で接続されている。ここで、「超電導的に接続」とは、圧接やスポット溶接の他、超電導半田等や超電導相を介した超電導体同士の接続を意味する。 A superconducting bypass element 15 is connected to both ends of the superconducting coil 11 via a first conducting wire 13 in a superconducting manner or with a sufficiently low resistance. Here, "superconductingly connected" means, in addition to pressure welding or spot welding, connecting superconductors to each other via superconducting solder or a superconducting phase.
　超電導バイパス素子１５は、超電導コイル１１に係る定格運転電流に対して十分に小さい（１％以下）電流容量を有する高温超電導体HTSよりなる。超電導バイパス素子１５に用いられる高温超電導体HTSとしては、特に限定されないが、例えば、二硼化マグネシウム（ＭｇＢ２）を好適に採用することができる。 The superconducting bypass element 15 is made of a high-temperature superconductor HTS having a sufficiently small (1% or less) current capacity with respect to the rated operating current of the superconducting coil 11. The high temperature superconductor HTS used in the superconducting bypass element 15 is not particularly limited, but for example, magnesium diboride (MgB 2 ) can be suitably employed.
　超電導バイパス素子１５は、励磁電源２３から供給される電流の変動成分に対し、同素子１５の電流容量と比べて小さい変動電流（ノイズ電流）をバイパスすることで超電導コイル１１への電流流入を抑制する一方、電流容量を越える大きさの電流を超電導コイル１１へ流す機能を有する。 The superconducting bypass element 15 suppresses current inflow into the superconducting coil 11 by bypassing a fluctuating current (noise current) that is smaller than the current capacity of the element 15 with respect to the fluctuating component of the current supplied from the excitation power source 23. On the other hand, it has a function of flowing a current exceeding the current capacity to the superconducting coil 11.
　従って、励磁過程においては、励磁電流が超電導バイパス素子１５の電流容量を越えると超電導コイル１１に電流が流れはじめ、電流掃引を止めると超電導コイル１１の流入電流は一定値に維持される。電流掃引を止めて一定の電流値に電源を維持していても、励磁電源２３からはノイズ電流が出力されている。
　ところが、このノイズ電流は、超電導バイパス素子１５の電流容量を越えない限り、超電導コイル１１へは流れない。
　従って、超電導コイル１１により発生される静磁場は、ノイズの影響を受けずに安定状態に保たれる。 Therefore, in the excitation process, when the excitation current exceeds the current capacity of the superconducting bypass element 15, current begins to flow into the superconducting coil 11, and when the current sweep is stopped, the current flowing into the superconducting coil 11 is maintained at a constant value. Even if the current sweep is stopped and the power source is maintained at a constant current value, a noise current is still output from the excitation power source 23.
However, this noise current does not flow to the superconducting coil 11 unless it exceeds the current capacity of the superconducting bypass element 15.
Therefore, the static magnetic field generated by the superconducting coil 11 is kept stable without being affected by noise.
　減磁過程においては、定常運転状態に逆向きの電流が追加投入されると考えることができる。そのため、励磁過程と同様に、励磁電源２３によってのみコイル電流を操作することが可能である。 In the demagnetization process, it can be considered that a current in the opposite direction is added to the steady operating state. Therefore, similarly to the excitation process, it is possible to manipulate the coil current only by the excitation power supply 23.
　励磁電源２３側からみた場合、超電導バイパス素子１５で短絡された超電導コイル１１は、永久電流モード運転で通常用いられる永久電流スイッチPCS（後記する図２に示す比較例の符号５３参照）の操作なしに（永久電流スイッチPCS５３にヒータ５７を設けずに）、励消磁を行うことができる。
　その結果、本発明の実施形態に係る超電導磁石装置１０によれば、超電導コイル１１が通常の電磁石のように振舞いながらも、永久電流モード運転と同等の磁場安定性を実現することができる。 When viewed from the excitation power source 23 side, the superconducting coil 11 short-circuited by the superconducting bypass element 15 does not operate the persistent current switch PCS (see reference numeral 53 in the comparative example shown in FIG. 2 described later) normally used in persistent current mode operation. (without providing the heater 57 in the persistent current switch PCS53), excitation and demagnetization can be performed.
As a result, according to the superconducting magnet device 10 according to the embodiment of the present invention, although the superconducting coil 11 behaves like a normal electromagnet, it is possible to achieve magnetic field stability equivalent to persistent current mode operation.
　超電導性の第１導線１３と、常電導性（例えば燐脱酸銅製）のパワーリード１７とは、はんだ付け等の接合手段によって常電導接続されている。同様に、常電導性のパワーリード１７と常電導性の第２導線１９とは、はんだ付け等の接合手段によって常電導接続されている。 The superconducting first conducting wire 13 and the normally conducting power lead 17 (made of phosphorus-deoxidized copper, for example) are connected in a normal conducting manner by a joining means such as soldering. Similarly, the normally conductive power lead 17 and the normally conductive second conducting wire 19 are connected to each other by a joining means such as soldering.
　超電導コイル１１を備える超電導回路１６には、第１導線１３及びパワーリード１７を介して、保護抵抗２５が並列接続されている。保護抵抗２５は、クエンチ時において、超電導コイル１１に蓄積されたエネルギーを回収する役割を果たす。 A protective resistor 25 is connected in parallel to the superconducting circuit 16 including the superconducting coil 11 via the first conducting wire 13 and the power lead 17. The protective resistor 25 plays the role of recovering the energy accumulated in the superconducting coil 11 during quenching.
　励磁電源２３は、第２導線１９、パワーリード１７、及び第１導線１３をそれぞれ介して、超電導コイル１１に直流の励磁電流を供給する役割を果たす。励磁電源２３が供給する励磁電流は、適宜の大きさに可変設定される。 The excitation power source 23 plays a role of supplying DC excitation current to the superconducting coil 11 via the second conductive wire 19, the power lead 17, and the first conductive wire 13, respectively. The excitation current supplied by the excitation power supply 23 is variably set to an appropriate magnitude.
　第２導線１９のうち励磁電源２３の両端には、一対の遮断器２１ａ、２１ｂが介挿接続されている。一対の遮断器２１ａ、２１ｂは、クエンチ時において、超電導コイル１１を備える超電導回路１６から励磁電源２３を切り離す役割を果たす。 A pair of circuit breakers 21a and 21b are inserted and connected to both ends of the excitation power source 23 of the second conducting wire 19. The pair of circuit breakers 21a and 21b serve to disconnect the excitation power source 23 from the superconducting circuit 16 including the superconducting coil 11 during quenching.
　本発明の実施形態に係る超電導磁石装置１０では、超電導コイル１１に係る定格運転電流と比べて小さい電流容量の超電導バイパス素子１５を超電導的に超電導コイル１１の両端に接続すると共に、超電導コイル１１を励磁するための励磁電源２３を超電導コイル１１に接続して運転を行う。すなわち、超電導コイル１１には、超電導バイパス素子１５及び保護抵抗２５が並列に接続されている。スイッチ素子である超電導バイパス素子１５は、高温超電導体HTSを線材として構成されており、超電導バイパス素子１５の電流容量は、超電導コイル１１に係る定格運転電流と比べて十分に小さい。 In the superconducting magnet device 10 according to the embodiment of the present invention, the superconducting bypass element 15 having a smaller current capacity than the rated operating current of the superconducting coil 11 is connected to both ends of the superconducting coil 11 in a superconducting manner, and the superconducting coil 11 is An excitation power source 23 for excitation is connected to the superconducting coil 11 for operation. That is, the superconducting bypass element 15 and the protective resistor 25 are connected to the superconducting coil 11 in parallel. The superconducting bypass element 15, which is a switch element, is configured using a high-temperature superconductor HTS as a wire, and the current capacity of the superconducting bypass element 15 is sufficiently smaller than the rated operating current of the superconducting coil 11.
　本発明の実施形態に係る超電導磁石装置１０において、超電導バイパス素子１５は、所定の磁場を発生している際には、低抵抗状態（スイッチオン状態）で超電導コイル１１を電気的に短絡する一方、磁場を変化させている際には、高抵抗状態（スイッチオフ状態）になり、励磁電源２３から超電導コイル１１への電流供給量を変更することで自発的（受動的）に開閉状態を変えるように動作する。 In the superconducting magnet device 10 according to the embodiment of the present invention, the superconducting bypass element 15 electrically short-circuits the superconducting coil 11 in a low resistance state (switch-on state) while generating a predetermined magnetic field. , when changing the magnetic field, it enters a high resistance state (switched off state), and changes the open/close state spontaneously (passively) by changing the amount of current supplied from the excitation power supply 23 to the superconducting coil 11. It works like this.
　本発明の実施形態に係る超電導磁石装置１０によれば、励磁電源２３から超電導コイル１１への電流供給量を変更することで超電導バイパス素子１５の開閉状態を自発的（受動的）に変更することで、励磁電源２３からの電流通電／遮断のみで超電導コイル１１を励磁／消磁するため、時間的に安定な磁場をドライブモード運転で実現することができる。 According to the superconducting magnet device 10 according to the embodiment of the present invention, the open/close state of the superconducting bypass element 15 can be spontaneously (passively) changed by changing the amount of current supplied from the excitation power source 23 to the superconducting coil 11. Since the superconducting coil 11 is excited/demagnetized only by turning on/off current from the excitation power source 23, a temporally stable magnetic field can be realized in drive mode operation.
〔比較例に係る超電導磁石装置５０の基本構成〕
　次に、比較例に係る超電導磁石装置５０の基本構成について図２を参照して説明する。
　図２は、比較例に係る超電導磁石装置５０の基本構成を表す回路図である。
　なお、図２では、図１と同様に、超電導体を線材としてなる導線等を太い実線で図示し、常電導体を線材としてなる導線等を細い実線で図示している。 [Basic configuration of superconducting magnet device 50 according to comparative example]
Next, the basic configuration of a superconducting magnet device 50 according to a comparative example will be described with reference to FIG. 2.
FIG. 2 is a circuit diagram showing the basic configuration of a superconducting magnet device 50 according to a comparative example.
In FIG. 2, as in FIG. 1, conductive wires made of a superconductor are shown as thick solid lines, and conductive wires made of a normal conductor are shown as thin solid lines.
　本発明の実施形態に係る超電導磁石装置１０と、比較例に係る超電導磁石装置５０とは、類似した基本構成の部分が存在する。そこで、前記両者の相違点に着目して説明することで、比較例に係る超電導磁石装置５０の基本構成の説明に代えることとする。 The superconducting magnet device 10 according to the embodiment of the present invention and the superconducting magnet device 50 according to the comparative example have similar basic configurations. Therefore, the description will focus on the differences between the two, instead of the description of the basic configuration of the superconducting magnet device 50 according to the comparative example.
　本発明の実施形態に係る超電導磁石装置１０では、図１に示すように、超電導回路１６は、高温超電導体HTSよりなる超電導コイル１１に、第１導線１３を介して、高温超電導体HTSよりなる超電導バイパス素子１５を並列接続して構成されるのに対し、比較例に係る超電導磁石装置５０では、図２に示すように、超電導回路５２は、超電導体（高温超電導体HTSではない）よりなる超電導コイル５１に、第１導線１３を介して、永久電流スイッチPCS５３を並列接続して構成される。 In the superconducting magnet device 10 according to the embodiment of the present invention, as shown in FIG. In contrast, in the superconducting magnet device 50 according to the comparative example, the superconducting circuit 52 is made of a superconductor (not the high-temperature superconductor HTS), as shown in FIG. A persistent current switch PCS 53 is connected in parallel to the superconducting coil 51 via the first conducting wire 13.
　比較例に係る超電導磁石装置５０において、超電導回路５２に属する永久電流スイッチPCS５３は、超電導体（高温超電導体HTSではない）よりなる超電導導線５５と、超電導導線５５を加熱するためのヒータ５７とを含んで構成される。ヒータ５７は、超電導導線５５に近接して設けられる。ヒータ５７には、ヒータ電源５９が接続されている。 In the superconducting magnet device 50 according to the comparative example, the persistent current switch PCS 53 belonging to the superconducting circuit 52 includes a superconducting wire 55 made of a superconductor (not a high-temperature superconductor HTS) and a heater 57 for heating the superconducting wire 55. It consists of: Heater 57 is provided close to superconducting wire 55 . A heater power source 59 is connected to the heater 57 .
　比較例に係る超電導磁石装置５０に備わる超電導回路５２では、第１導線１３及びパワーリード１７を介して直列接続された励磁電源２３からの電流供給を受けて、超電導コイル５１及び超電導導線５５を含む超電導回路５２内に所定の永久電流を循環させる。これにより、超電導回路５２は、超電導コイル５１において磁場を発生させる。 A superconducting circuit 52 provided in a superconducting magnet device 50 according to a comparative example receives a current supply from an excitation power source 23 connected in series via a first conductive wire 13 and a power lead 17, and includes a superconducting coil 51 and a superconducting conductive wire 55. A predetermined persistent current is circulated within the superconducting circuit 52. Thereby, the superconducting circuit 52 generates a magnetic field in the superconducting coil 51.
　また、比較例に係る超電導磁石装置５０に備わる超電導回路５２において、超電導導線５５をヒータ５７で加熱し、超電導導線５５の温度が所定の超電導臨界温度を超えると、超電導導線５５が超電導状態から常電導状態に転移する（つまり、永久電流スイッチPCS５３がオフ状態になる）。
　その後、ヒータ５７による加熱を止めて、超電導臨界温度以下になるまで超電導導線５５を冷却すると、超電導導線５５が超電導状態に転移する（つまり、永久電流スイッチPCS５３がオン状態になる）。 In addition, in the superconducting circuit 52 provided in the superconducting magnet device 50 according to the comparative example, when the superconducting wire 55 is heated by the heater 57 and the temperature of the superconducting wire 55 exceeds a predetermined superconducting critical temperature, the superconducting wire 55 changes from the superconducting state to the normal state. It transitions to a conductive state (that is, the persistent current switch PCS53 turns off).
Thereafter, when the heating by the heater 57 is stopped and the superconducting wire 55 is cooled down to below the superconducting critical temperature, the superconducting wire 55 transitions to a superconducting state (that is, the persistent current switch PCS 53 is turned on).
〔本発明の実施形態に係る超電導磁石装置１０の基本実装状態〕
　次に、本発明の実施形態に係る超電導磁石装置１０の基本実装状態について図３を参照して説明する。
　図３は、本発明の実施形態に係る超電導磁石装置１０の基本実装状態を表す概念図である。 [Basic mounting state of superconducting magnet device 10 according to the embodiment of the present invention]
Next, the basic mounting state of the superconducting magnet device 10 according to the embodiment of the present invention will be described with reference to FIG. 3.
FIG. 3 is a conceptual diagram showing the basic mounting state of the superconducting magnet device 10 according to the embodiment of the present invention.
　本発明の実施形態に係る超電導磁石装置１０に備わる超電導回路１６は、図３に示すように、断熱真空容器であるクライオスタット１８に収容されている。クライオスタット１８は、電動冷凍機（図９の符号３１参照）、液体のヘリウム、窒素、水素、アルゴン等を用いて、クライオスタット１８の室内温度を所定の超電導臨界温度以下に冷却するように構成されている。 As shown in FIG. 3, the superconducting circuit 16 included in the superconducting magnet device 10 according to the embodiment of the present invention is housed in a cryostat 18, which is an insulated vacuum container. The cryostat 18 is configured to cool the indoor temperature of the cryostat 18 to below a predetermined superconducting critical temperature using an electric refrigerator (see reference numeral 31 in FIG. 9), liquid helium, nitrogen, hydrogen, argon, etc. There is.
　クライオスタット１８には、パワーリード１７を挿通するための一対の通孔２０が開設されている。この一対の通孔２０に挿通された状態で、超電導回路１６に連なる一対のパワーリード１７が、クライオスタット１８に固定されている。パワーリード１７のうち励磁電源２３接続側は、クライオスタット１８の室外に露出している。 The cryostat 18 has a pair of through holes 20 for inserting the power lead 17 therethrough. A pair of power leads 17 connected to the superconducting circuit 16 are fixed to the cryostat 18 while being inserted through the pair of through holes 20 . The side of the power lead 17 connected to the excitation power source 23 is exposed to the outside of the cryostat 18 .
〔磁場安定化の原理〕
　次に本発明の実施形態に係る超電導磁石装置１０が実現する磁場安定化の原理について、図４を参照して説明する。
　図４は、本発明の実施形態に係る超電導磁石装置１０が実現する磁場安定化の原理を説明するための等価回路図である。 [Principle of magnetic field stabilization]
Next, the principle of magnetic field stabilization realized by the superconducting magnet device 10 according to the embodiment of the present invention will be described with reference to FIG. 4.
FIG. 4 is an equivalent circuit diagram for explaining the principle of magnetic field stabilization realized by the superconducting magnet device 10 according to the embodiment of the present invention.
　まず、超電導磁石装置１０の等価回路図として、図４に示すように、インダクタンスＬと抵抗Ｒの並列回路に電流源Ｉが接続された回路を考える。同等価回路において、超電導コイル１１との接続抵抗を含めた超電導バイパス素子１５の電気抵抗をＲとし、超電導コイル１１のインダクタンスをＬとして、電流源をＩとする。
　同等価回路において、電流源Ｉからみると、超電導バイパス素子１５によって時定数τ=L/R、カットオフ周波数fc=R/2πLのローパスフィルタが形成されたことになる。
　電流源Ｉからの交流ノイズについては、ノイズの周波数に合わせて、適切なカットオフ周波数になるような抵抗Ｒ（引き回し線抵抗及び接続抵抗を含む）となる等価回路を構成すればよい。 First, as an equivalent circuit diagram of the superconducting magnet device 10, consider a circuit in which a current source I is connected to a parallel circuit of an inductance L and a resistor R, as shown in FIG. In the equivalent circuit, let R be the electrical resistance of the superconducting bypass element 15 including the connection resistance with the superconducting coil 11, L be the inductance of the superconducting coil 11, and I be the current source.
In the equivalent circuit, when viewed from the current source I, the superconducting bypass element 15 forms a low-pass filter with a time constant τ=L/R and a cutoff frequency fc=R/2πL.
Regarding alternating current noise from the current source I, an equivalent circuit may be constructed that has a resistance R (including wiring resistance and connection resistance) that has an appropriate cutoff frequency in accordance with the frequency of the noise.
　ここで問題になるのがＤＣ成分（ドリフト）である。これは極めて長い時定数で変動する周期性のノイズの一部分と考えることができる。これについても、例えば周期が1日２４時間の周期で変動するものと考えてカットオフ周波数fcを適宜設定すれば良い。
　しかし、この考え方によれば極めて小さな値の抵抗Ｒが要求される。そこで、ＤＣ成分に対しては以下のように考える。
　すなわち、図４に示す等価回路において、電流源Ｉから供給される電流の時間変化Ｉ（ｔ）を（式１）のように考える。
Figure JPOXMLDOC01-appb-M000001
 The problem here is the DC component (drift). This can be considered as part of periodic noise that fluctuates with an extremely long time constant. Regarding this as well, the cutoff frequency fc may be appropriately set by considering that the period varies in a 24-hour period, for example.
However, this concept requires a resistance R of extremely small value. Therefore, consider the DC component as follows.
That is, in the equivalent circuit shown in FIG. 4, the time change I(t) of the current supplied from the current source I is considered as shown in (Equation 1).
Figure JPOXMLDOC01-appb-M000001
　Ｉ0は設定電流値であり、ａは単位時間あたりの変動量である。これに対して、コイル（超電導コイル１１）に流れる電流ＩLと、抵抗（超電導バイパス素子１５）に流れる電流ＩRの関係は（式２）のように記述することができる。
Figure JPOXMLDOC01-appb-M000002
 I0 is the set current value, and a is the amount of variation per unit time. On the other hand, the relationship between the current IL flowing in the coil (superconducting coil 11) and the current IR flowing in the resistor (superconducting bypass element 15) can be described as (Equation 2).
Figure JPOXMLDOC01-appb-M000002
　ここで、次の微分方程式（式３）を立てる。
Figure JPOXMLDOC01-appb-M000003
 Here, the following differential equation (Equation 3) is established.
Figure JPOXMLDOC01-appb-M000003
　微分方程式（式３）を解くと、電流変動は（式４）のように記述することができる。
Figure JPOXMLDOC01-appb-M000004
 When the differential equation (Equation 3) is solved, the current fluctuation can be described as in (Equation 4).
Figure JPOXMLDOC01-appb-M000004
　この（式４）は、時間の経過とともに超電導コイル１１（コイルＬ）に流れる電流ＩLは電源源Ｉの電流ドリフト速度aによって支配されることを示している。実際には磁場を利用する時間の間にのみ所定の安定磁場が維持されていればよく、時定数τ=L/Rと比べて時間tが十分に小さいときには（式５）の関係が得られる。
Figure JPOXMLDOC01-appb-M000005
 This (Equation 4) indicates that the current IL flowing through the superconducting coil 11 (coil L) over time is controlled by the current drift speed a of the power source I. In reality, it is sufficient that a predetermined stable magnetic field is maintained only during the time when the magnetic field is used, and when the time t is sufficiently small compared to the time constant τ=L/R, the relationship (Equation 5) is obtained. .
Figure JPOXMLDOC01-appb-M000005
　例えば、電流ドリフトの変化率を１時間あたり０．１％とし、磁場の利用時間１時間において磁場の安定度が０．１ｐｐｍ必要であるとし、超電導コイル１１のインダクタンスＬを９６Ｈとすれば、それを満たす抵抗値は５．３マイクロオーム以下となる。この時の時定数τはおよそ５０００時間となり、カットオフ周波数は８．８ｎＨｚとなり、１０Ｈｚの電流ノイズはおよそ９桁小さくなる。
　このように、超電導コイル１１をマイクロオームオーダーの抵抗（超電導バイパス素子１５）で短絡することによって、磁場の安定化を実現することができることがわかった。 For example, if the rate of change of current drift is 0.1% per hour, the stability of the magnetic field is required to be 0.1 ppm in one hour of magnetic field use, and the inductance L of the superconducting coil 11 is 96H, then The resistance value that satisfies this requirement is 5.3 microohms or less. The time constant τ at this time is about 5000 hours, the cutoff frequency is 8.8 nHz, and the 10 Hz current noise is reduced by about 9 orders of magnitude.
In this way, it has been found that by short-circuiting the superconducting coil 11 with a microohm-order resistance (superconducting bypass element 15), stabilization of the magnetic field can be achieved.
　一方、超電導コイル１１をこのような極めて小さい抵抗（超電導バイパス素子１５）で短絡すると、電流源Ｉから電流投入を試みても、その試みを果たすことはできない。そこで、磁石を励磁する場合には、いったんこの短絡抵抗を切ってから電流を通電し、所定の電流を通電した後に短絡させる操作が必要となる。 On the other hand, if the superconducting coil 11 is short-circuited with such an extremely small resistance (superconducting bypass element 15), even if an attempt is made to supply current from the current source I, the attempt cannot be made. Therefore, in order to excite the magnet, it is necessary to first turn off this short-circuit resistance, then apply current, and then short-circuit the magnet after a predetermined current has been applied.
〔超電導バイパス素子１５のオンオフ制御〕
　超電導バイパス素子１５は、コイル（超電導コイル１１）への電流投入又はコイルから電流を引き出す際にはオフ状態にする一方、一定磁場の発生・利用時にはオン状態にすることが必要である。
　ここで、比較例に係る永久電流スイッチPCS５３（図２参照）のように、超電導バイパス素子１５に近接してヒータ５７を設けることにより、超電導バイパス素子１５をオンオフする実装も考えられる。しかしながら、このオンオフ制御に係るスイッチング動作は、ユーザが全く意識することなく自発的（受動的）に実現されることが望ましい。 [On/off control of superconducting bypass element 15]
The superconducting bypass element 15 needs to be turned off when applying current to the coil (superconducting coil 11) or drawing current from the coil, but turned on when generating and using a constant magnetic field.
Here, implementation can be considered in which the superconducting bypass element 15 is turned on and off by providing a heater 57 close to the superconducting bypass element 15, like the persistent current switch PCS53 (see FIG. 2) according to the comparative example. However, it is desirable that the switching operation related to this on/off control be realized spontaneously (passively) without the user being aware of it at all.
　そこで、本発明に係る超電導磁石装置１０では、コイル（超電導コイル１１）の定格運転電流に対して十分に小さい臨界電流特性を有する（例えば１％の）高温超電導体HTSからなる線材を用いて超電導バイパス素子１５を実装することとした。 Therefore, in the superconducting magnet device 10 according to the present invention, a wire made of a high-temperature superconductor HTS having a sufficiently small critical current characteristic (for example, 1%) with respect to the rated operating current of the coil (superconducting coil 11) is used to conduct superconducting. We decided to mount the bypass element 15.
　（式５）に示すように、超電導バイパス素子１５によって両端が短絡されたコイル（超電導コイル１１）に、電流源Ｉから電流投入を試みても、コイルにはほとんど電流を投入することはできず、ほぼ全ての電流が超電導バイパス素子１５を流れることとなる。
　超電導バイパス素子１５の電流容量（臨界電流値）をコイルの定格運転電流に対して十分に小さく（例えば１％程度）しておくことにより、電流源Ｉからの電流掃引開始後に超電導バイパス素子１５に流れた電流は、臨界電流値にすぐに到達し超電導バイパス素子１５を常電導状態（高抵抗状態：スイッチオフ状態）に遷移させる。 As shown in (Formula 5), even if an attempt is made to inject current from current source I into the coil (superconducting coil 11) whose ends are short-circuited by superconducting bypass element 15, almost no current can be injected into the coil. , almost all of the current flows through the superconducting bypass element 15.
By keeping the current capacity (critical current value) of the superconducting bypass element 15 sufficiently small (for example, about 1%) with respect to the rated operating current of the coil, the superconducting bypass element 15 can be The flowing current quickly reaches a critical current value and causes the superconducting bypass element 15 to transition to a normal conduction state (high resistance state: switch-off state).
　前記したような超電導バイパス素子１５の実装によれば、比較例に係る永久電流スイッチPCS５３のように能動的にヒータ５７を駆動することなく、超電導バイパス素子１５を自発的（受動的）に超電導を常電導に転移させることにより、オンオフ制御に係るスイッチング動作を実現することができる。 According to the implementation of the superconducting bypass element 15 as described above, the superconducting bypass element 15 spontaneously (passively) performs superconducting without actively driving the heater 57 like the persistent current switch PCS53 according to the comparative example. By making the transition to normal conductivity, a switching operation related to on/off control can be realized.
　励磁過程における電流源Ｉからの供給電流の時間変化と磁場発生（コイル電流）の時間変化の模式図を図５に示す。図５の実線は電流源Ｉからの供給電流の時間変化を、破線は発生磁場（コイル電流）の時間変化をそれぞれ表す。
　電流掃引された直後には超電導バイパス素子１５に流れている電流は臨界電流値に到達しておらず、素子１５は超電導状態が維持され、しばらくの間、コイル（超電導コイル１１）には電流が流れない（図５に示す時刻ｔ０－ｔ５１の区間参照）。
　超電導バイパス素子１５の電気抵抗Ｒが発生しはじめるとコイルにも電流が流れ始め、十分に時間がたつとコイルに流れる電流の増加速度が電流源Ｉの電流掃引速度と一致する（図５に示す時刻ｔ５１－ｔ５２の区間参照）。
　電源掃引を止めると（図５に示す時刻ｔ５２参照）、コイルのインダクタンスと超電導バイパス素子１５の常電導抵抗で決まる時定数に従って、コイル電流は電流源Ｉから供給される電流値に漸近し一致する（図５に示す時刻ｔ５２以降の区間参照）。 FIG. 5 shows a schematic diagram of the time change in the supply current from the current source I and the time change in magnetic field generation (coil current) during the excitation process. The solid line in FIG. 5 represents the time change in the current supplied from the current source I, and the broken line represents the time change in the generated magnetic field (coil current).
Immediately after the current sweep, the current flowing through the superconducting bypass element 15 has not reached the critical current value, the element 15 maintains its superconducting state, and no current flows through the coil (superconducting coil 11) for a while. It does not flow (see the section from time t0 to time t51 shown in FIG. 5).
When the electrical resistance R of the superconducting bypass element 15 begins to occur, current also begins to flow in the coil, and after a sufficient period of time, the rate of increase in the current flowing in the coil matches the current sweep rate of the current source I (as shown in FIG. 5). (See the section from time t51 to time t52).
When the power supply sweep is stopped (see time t52 shown in FIG. 5), the coil current asymptotically approaches and matches the current value supplied from the current source I according to the time constant determined by the inductance of the coil and the normal conduction resistance of the superconducting bypass element 15. (See the section after time t52 shown in FIG. 5).
　減磁過程についても同様である。減磁過程における電流源Ｉからの供給電流の時間変化と磁場発生（コイル電流）の時間変化の模式図を図６に示す。図６の実線は電流源Ｉからの供給電流の時間変化を、破線は発生磁場（コイル電流）の時間変化をそれぞれ表す。
　一定値で運転されているところ（図６に示す時刻ｔ６１以前の区間参照）から、電流源Ｉの供給電流値を線形に漸減させていく（図６に示す時刻ｔ６１以降の区間参照）。コイル及び超電導バイパス素子１５からは、電流源Ｉから逆向きの電流が重畳されて掃引されるようにみえ、この逆向き電流に関して励磁過程と同じ現象が起こる。 The same applies to the demagnetization process. FIG. 6 shows a schematic diagram of the time change in the current supplied from the current source I and the time change in magnetic field generation (coil current) during the demagnetization process. The solid line in FIG. 6 represents the time change of the supplied current from the current source I, and the broken line represents the time change of the generated magnetic field (coil current).
The supply current value of the current source I is gradually decreased linearly from the point where the current source I is operated at a constant value (see the section before time t61 shown in FIG. 6) (see the section after time t61 shown in FIG. 6). From the coil and the superconducting bypass element 15, it appears that a current in the opposite direction from the current source I is superimposed and swept, and the same phenomenon as in the excitation process occurs regarding this reverse direction current.
　電流掃引された直後には、超電導バイパス素子１５に流れはじめた逆向き電流は臨界電流値に到達しておらず、素子は超電導状態が維持され、しばらくの間はコイルには電流は維持されたままとなりほとんど変化はない（図６に示す時刻ｔ６１－ｔ６２の区間参照）。時間がたって臨界電流値に到達し、超電導バイパス素子１５の電気抵抗が発生しはじめると、コイルにも電流が流れ始め、十分に時間がたつとコイルに流れる電流の減少速度が電流源Ｉの電流掃引速度と一致する（図６に示す時刻ｔ６２以降の区間参照）。
　電流源Ｉからの通電電流がゼロになると（図６に示す時刻ｔ６３参照）、コイルのインダクタンスと超電導バイパス素子１５の常電導抵抗で決まる時定数に従ってコイル電流はゼロに漸近する。 Immediately after the current sweep, the reverse current that started flowing through the superconducting bypass element 15 had not reached the critical current value, the element maintained its superconducting state, and the current was maintained in the coil for a while. There is almost no change (see the section from time t61 to time t62 shown in FIG. 6). When a critical current value is reached over time and electrical resistance of the superconducting bypass element 15 begins to occur, current also begins to flow in the coil, and after a sufficient period of time, the rate of decrease in the current flowing through the coil becomes equal to the current of current source I. It matches the sweep speed (see the section after time t62 shown in FIG. 6).
When the current flowing from the current source I becomes zero (see time t63 shown in FIG. 6), the coil current approaches zero according to a time constant determined by the inductance of the coil and the normal conduction resistance of the superconducting bypass element 15.
　このように、比較例に係る永久電流スイッチPCS５３（図２参照）を備える超電導磁石装置５０のように、ヒータ５７のオンオフや電流を合わせる操作を意識することなく、単に電流源Ｉに係る電流供給量を操作することのみによって、磁石（超電導コイル１１）を励消磁することが可能となる。 In this way, like the superconducting magnet device 50 equipped with the persistent current switch PCS53 (see FIG. 2) according to the comparative example, the current supply from the current source I can be performed without being conscious of turning on/off the heater 57 or adjusting the current. It becomes possible to excite and demagnetize the magnet (superconducting coil 11) only by manipulating the amount.
　しかし、電源電流とコイル電流が一致するまでに所定の待ち時間が生じることは、予め考慮しておかなければならない。 However, it must be taken into consideration in advance that a predetermined waiting time will occur until the power supply current and coil current match.
　コイル（超電導コイル１１）への電流供給量を変更することで発生磁場強度を変更する際において、電流変化量が小さい場合には、図７に示すように、一旦供給電流を下げる（図７に示す時刻ｔ７１－時刻ｔ７３の区間参照）ことで超電導バイパス素子１５をオフにした（図７に示す時刻ｔ７３参照）あと、再度電流を追加（図７に示す時刻ｔ７３－時刻ｔ７５の区間参照）して電流値を合わせるような操作も必要となる。 When changing the generated magnetic field strength by changing the amount of current supplied to the coil (superconducting coil 11), if the amount of current change is small, the supplied current is temporarily lowered as shown in Figure 7. After turning off the superconducting bypass element 15 (see the interval from time t71 to time t73 shown in FIG. 7), the current is added again (see the interval from time t73 to time t75 shown in FIG. 7). It is also necessary to perform operations such as adjusting the current value.
　ジュール熱によって超電導バイパス素子１５を完全に常電導状態にするためには十分なエネルギー（発熱量）が必要であり、それは超電導バイパス素子１５を構成する高温超電導体HTSの常電導抵抗と超電導バイパス素子１５に流れる電流の２乗積で決まるジュール発熱と発熱継続時間で決まる。 Sufficient energy (calorific value) is required to completely bring the superconducting bypass element 15 into a normal conducting state using Joule heat, and this is due to the normal conducting resistance of the high temperature superconductor HTS that constitutes the superconducting bypass element 15 and the superconducting bypass element. It is determined by Joule heat generation, which is determined by the square product of the current flowing through 15, and the heat generation duration time.
　従って、短時間で超電導バイパス素子１５を抵抗状態に転移させるために、図８に示すように、急激に電流を立ち上げて、超電導バイパス素子１５の発熱を瞬間的に大きくした（プレ通電運転：図８に示す時刻ｔ８１－時刻ｔ８２の区間参照）後、電流掃引を開始することによって、時間遅れ（図８に示す時刻ｔ８２－時刻ｔ８３に係る時間長を参照）を短くすることができる。
　従って、前記電流掃引開始前のプレ通電における電流掃引速度や電流投入量を設計・制御すれば、超電導バイパス素子１５を抵抗状態に転移させるのに要する時間及びコイルへの電流の投入速度を制御することができる。 Therefore, in order to transition the superconducting bypass element 15 to the resistance state in a short time, as shown in FIG. 8, the current is suddenly increased to instantly increase the heat generation of the superconducting bypass element 15 (pre-energization operation: By starting the current sweep after the interval from time t81 to time t82 shown in FIG. 8), the time delay (see the time length from time t82 to time t83 shown in FIG. 8) can be shortened.
Therefore, by designing and controlling the current sweep speed and current input amount in the pre-energization before the start of the current sweep, the time required to transition the superconducting bypass element 15 to the resistance state and the current input speed to the coil can be controlled. be able to.
　超電導バイパス素子１５の電流容量は、電流源Ｉのリップルノイズ電流の分だけを通電できれば十分であり、大きすぎる電流容量は超電導バイパス素子１５を電圧発生状態にするために大きな電流を必要とすることから無駄となる。
　従って、超電導バイパス素子１５の電流容量は、超電導コイル１１に係る定格運転電流の１％未満程度、電流としては１A未満程度が目安となる。 The current capacity of the superconducting bypass element 15 is sufficient as long as it can pass the ripple noise current of the current source I, and if the current capacity is too large, a large current is required to bring the superconducting bypass element 15 into a voltage generating state. It becomes wasted.
Therefore, the current capacity of the superconducting bypass element 15 is approximately less than 1% of the rated operating current of the superconducting coil 11, and the current is approximately less than 1 A.
〔超電導コイル１１及び超電導バイパス素子１５の設計〕
　超電導コイル１１のクエンチ時や異常時の緊急遮断後には、HTS磁石では超電導コイル１１に蓄積されたエネルギーを速やかに回収する必要がある。HTS磁石ではクエンチ伝搬速度が遅いことから、超電導コイル１１でのエネルギー回収はあまり期待できない。そのため、外部に設けた保護抵抗２５によって超電導コイル１１に蓄積されたエネルギーを回収する。超電導コイル１１を焼損させないために、１０オーム程度の抵抗値を有する保護抵抗２５が必要となる。 [Design of superconducting coil 11 and superconducting bypass element 15]
When the superconducting coil 11 is quenched or after an emergency shutdown in the event of an abnormality, the HTS magnet needs to quickly recover the energy accumulated in the superconducting coil 11. Since the quench propagation speed is slow in the HTS magnet, energy recovery in the superconducting coil 11 cannot be expected much. Therefore, the energy accumulated in the superconducting coil 11 is recovered by the protective resistor 25 provided outside. In order to prevent superconducting coil 11 from burning out, protective resistor 25 having a resistance value of about 10 ohms is required.
　超電導バイパス素子１５が抵抗状態（スイッチオフ状態）である場合、超電導コイル１１の蓄積エネルギーは保護抵抗２５と超電導バイパス素子１５に係るノーマル抵抗（スイッチオフ状態における電気抵抗）の逆比例でそれぞれに配分されて熱として回収される。
　保護抵抗２５に対して超電導バイパス素子１５のノーマル抵抗が十分に大きくないケースでは、磁石のエネルギーは超電導バイパス素子１５が設けられているクライオスタット１８内部で回収されるため、再冷却に時間を要する。また、超電導バイパス素子１５それ自体の焼損防止のための熱容量が必要となる。 When the superconducting bypass element 15 is in a resistance state (switch-off state), the accumulated energy of the superconducting coil 11 is distributed to the protective resistor 25 and the normal resistance (electrical resistance in the switch-off state) of the superconducting bypass element 15 in inverse proportion to each other. and recovered as heat.
In the case where the normal resistance of the superconducting bypass element 15 is not sufficiently large with respect to the protective resistor 25, the energy of the magnet is recovered inside the cryostat 18 in which the superconducting bypass element 15 is provided, so that recooling takes time. Further, a heat capacity is required to prevent the superconducting bypass element 15 itself from being burnt out.
　従って、超電導バイパス素子１５のスイッチオフ状態における電気抵抗の値は、保護抵抗２５の電気抵抗の値と比べて１０倍以上、好ましくは３０倍以上の値に設定される。
　このように構成すれば、超電導バイパス素子１５それ自体の焼損防止のための熱容量を抑制する効果を期待することができる。 Therefore, the value of the electrical resistance of the superconducting bypass element 15 in the switch-off state is set to a value that is 10 times or more, preferably 30 times or more, as compared to the value of the electrical resistance of the protective resistor 25.
With this configuration, it is possible to expect the effect of suppressing the heat capacity to prevent burnout of the superconducting bypass element 15 itself.
　そこで、超電導バイパス素子１５のスイッチオフ状態における電気抵抗の値が１００－３００オームとなるように設計を行なった。 Therefore, the superconducting bypass element 15 was designed so that the electrical resistance value in the switch-off state was 100-300 ohms.
　ここで、超電導コイル１１は、ニオブチタン合金（Nb-Ti）を母材する線材直径０．６４ｍｍの二硼化マグネシウム（ＭｇＢ２）超電導単芯線材を８５ｍ巻き回して製作した。同様に、超電導バイパス素子１５も、前記二硼化マグネシウム（ＭｇＢ２）超電導単芯線材を用いて製作した。この超電導単芯線材の４０Ｋにおける抵抗率は、設計上38×10^-8 オームメートルであり、このときの電気抵抗の値は１００オームである。 Here, the superconducting coil 11 was manufactured by winding 85 m of a magnesium diboride (MgB 2 ) superconducting single core wire with a wire diameter of 0.64 mm and having a base material of niobium titanium alloy (Nb-Ti). Similarly, the superconducting bypass element 15 was also manufactured using the magnesium diboride (MgB 2 ) superconducting single core wire. The resistivity of this superconducting single core wire at 40K is designed to be 38 x 10^-8 ohm meters, and the electrical resistance value at this time is 100 ohms.
　一般に、臨界電流値は、電界が1×10^-4[V/m] 発生したときの電流で規定される。本実施形態のケースでは、超電導コイル１１の線材長は８５ｍであるので、超電導バイパス素子１５に臨界電流値に相当する電流が流れている時に同素子１５に発生する電圧は８．５ｍＶとなる。この時には、超電導バイパス素子１５に発生した電圧（８．５ｍＶ）で超電導コイル１１が励磁されると考えることができる。
　この電圧によって超電導コイル１１へ投入される電流の増加速度は、超電導コイル１１のインダクタンスが９６Ｈであるので、８９μＡ／秒となる。この条件では定格運転電流（２５０Ａ）まで励磁するには７８０時間もの時間がかかることになり、現実的でない。 Generally, the critical current value is defined as the current when an electric field of 1×10^-4 [V/m] is generated. In the case of this embodiment, since the wire length of the superconducting coil 11 is 85 m, the voltage generated in the superconducting bypass element 15 when a current corresponding to the critical current value flows through the element 15 is 8.5 mV. At this time, it can be considered that the superconducting coil 11 is excited by the voltage (8.5 mV) generated in the superconducting bypass element 15.
Since the inductance of the superconducting coil 11 is 96H, the rate of increase in the current applied to the superconducting coil 11 by this voltage is 89 μA/sec. Under these conditions, it would take as much as 780 hours to excite the magnet to the rated operating current (250 A), which is not realistic.
　超電導体の電流電圧特性は、（式６）に示すようなベキ乗のかたちの非線形特性で記述することができる。
Figure JPOXMLDOC01-appb-M000006
 The current-voltage characteristics of a superconductor can be described by a power-law nonlinear characteristic as shown in (Equation 6).
Figure JPOXMLDOC01-appb-M000006
　（式６）において、仮にｎ＝１０とした場合、臨界電流の２倍の値の電流を流すとすれば、臨界電流時に比べると電圧発生は１０００倍となり、励磁時間は１／１０００に短縮されて現実的な値となる。このとき、超電導バイパス素子１５では約９Ｖの電圧が発生する。つまり、およそ１０Ｖの電圧発生が現実的な時間で励磁できる目安となる。
　このように励磁速度を決めるのは電圧であって、１００オームのフル抵抗を発生させる必要はない。従って、図２に示す比較例に係る永久電流スイッチPCS５３のようにヒータ５７を用いて温度を上げることは必ずしも本質ではなく、超電導バイパス素子１５に電圧を発生させることが本質（供給電流量だけでコントロールできるため）となる。 In (Equation 6), if n = 10 and a current twice the value of the critical current is passed, the voltage generation will be 1000 times that of the critical current, and the excitation time will be shortened to 1/1000. This is a realistic value. At this time, a voltage of approximately 9V is generated in the superconducting bypass element 15. In other words, generation of a voltage of approximately 10V is a guideline for excitation within a realistic time.
In this way, it is the voltage that determines the excitation speed, and there is no need to create a full resistance of 100 ohms. Therefore, it is not necessarily essential to raise the temperature using the heater 57 as in the persistent current switch PCS53 according to the comparative example shown in FIG. (because it can be controlled).
　超電導バイパス素子１５の電流容量は、電流性ノイズを透過させるための容量さえあればよく、上記のように電圧発生の観点から小さいことが望ましい。
　従って、超電導バイパス素子１５の電流容量は、超電導コイル１１に係る定格運転電流に対して１％以下（又は１Ａ以下）が目安となる。 The current capacity of the superconducting bypass element 15 only needs to have a capacity for transmitting current noise, and as mentioned above, it is desirable to have a small current capacity from the viewpoint of voltage generation.
Therefore, the current capacity of the superconducting bypass element 15 is approximately 1% or less (or 1 A or less) with respect to the rated operating current of the superconducting coil 11.
〔微小電流容量の実現方法〕
　ニオブチタン合金（Ｎｂ－Ｔｉ）、ニオブスズ（Ｎｂ３Ｓｎ）といった実用的な低温超電導体に比べると、高温超電導体HTSは超電導フィラメントの細線化が困難である。具体的には、銅酸化物超電導体（REBCO）、ビスマス系超電導体（BSCCO）、二硼化マグネシウム（ＭｇＢ２）などの高温超電導体HTSを線材として用いるケースでは、超電導コイル１１（定格運転電流：１００Ａ－３００Ａ）に対し、その定格運転電流の１％の電流容量の超電導バイパス素子１５を細線化によって実現することはほとんど不可能である。 [Method for realizing micro current capacity]
Compared to practical low-temperature superconductors such as niobium-titanium alloy (Nb-Ti) and niobium-tin (Nb 3 Sn), it is difficult to thin the superconducting filament of high-temperature superconductor HTS. Specifically, in cases where high-temperature superconductor HTS such as copper oxide superconductor (REBCO), bismuth-based superconductor (BSCCO), and magnesium diboride (MgB 2 ) is used as the wire material, superconducting coil 11 (rated operating current :100A-300A), it is almost impossible to realize a superconducting bypass element 15 with a current capacity of 1% of the rated operating current by thinning the wire.
　そこで、超電導コイル１１の定格運転温度と比べて高い温度領域に属する場所に超電導バイパス素子１５を設ける。この温度領域に係る温度範囲は、超電導バイパス素子１５の臨界温度未満であって該臨界温度に対して５Ｋ以内に設定される。
　このように、超電導バイパス素子１５を、超電導コイル１１の定格運転温度と比べて高い温度領域に属する場所に設け、超電導バイパス素子１５を臨界温度付近で動作させることによって、超電導コイル１１に係る定格運転電流の１％オーダーの電流容量を有する超電導バイパス素子１５を実現する。
　その結果、超電導バイパス素子１５を比較的高温の雰囲気環境に設置することにより、わずかなジュール発熱によっても常電導状態に転移させることができるため、超電導バイパス素子１５を容易に抵抗状態（スイッチオフ状態）に遷移させることができる。 Therefore, the superconducting bypass element 15 is provided at a location that belongs to a temperature range higher than the rated operating temperature of the superconducting coil 11. The temperature range related to this temperature region is set below the critical temperature of the superconducting bypass element 15 and within 5K with respect to the critical temperature.
In this way, by providing the superconducting bypass element 15 at a location that belongs to a temperature range higher than the rated operating temperature of the superconducting coil 11 and operating the superconducting bypass element 15 near the critical temperature, the rated operating temperature of the superconducting coil 11 can be achieved. A superconducting bypass element 15 having a current capacity on the order of 1% of current is realized.
As a result, by installing the superconducting bypass element 15 in a relatively high-temperature atmosphere environment, it can be transferred to the normal conductive state even with a slight Joule heat generation, so that the superconducting bypass element 15 can easily be placed in the resistance state (switched off state). ).
　さらに、図２に示す比較例に係る永久電流スイッチPCS５３では、無誘導巻線化してインダクタンスを限りなくゼロにすることが多いところ、本発明に係る実施形態では、超電導バイパス素子１５を誘導巻線化することによって、励消磁時に超電導バイパス素子１５に発生する自己磁場によって電流輸送特性を低下させるようにしている。 Furthermore, in the persistent current switch PCS 53 according to the comparative example shown in FIG. 2, the inductance is often reduced to zero by using non-inductive winding, but in the embodiment according to the present invention, the superconducting bypass element 15 is inductively wound. By doing so, the current transport characteristics are reduced by the self-magnetic field generated in the superconducting bypass element 15 during excitation and demagnetization.
　超電導コイル１１に係る定格運転電流の１％以下の電流容量を実現するために、超電導体の臨界温度直下となるように、超電導バイパス素子１５の設置場所に係る雰囲気環境温度を設定する。
　臨界温度付近では磁場に対して感受性が敏感になり、より効果的に電流容量を小さくすることができる。その結果、制御性のよい超電導バイパス素子１５を実現することができる。 In order to achieve a current capacity of 1% or less of the rated operating current of the superconducting coil 11, the ambient temperature at the location where the superconducting bypass element 15 is installed is set to be just below the critical temperature of the superconductor.
Near the critical temperature, it becomes sensitive to magnetic fields, making it possible to more effectively reduce the current capacity. As a result, a superconducting bypass element 15 with good controllability can be realized.
　誘導巻線化された超電導バイパス素子１５は、インダクタンスを持つことになり、超電導コイル１１と超電導バイパス素子１５のインピーダンスの逆比をもって、ノイズ電流が超電導コイル１１と超電導バイパス素子１５に分配されることになる。超電導コイル１１のインダクタンスは１００Ｈのオーダーであり、超電導バイパス素子１５のインダクタンスを１ｍＨのオーダーで構成することによって、リップルノイズの混入を略十万分の一に低下することができる。リップルノイズは1×10^-3と比べて十分に小さい。
　従って、超電導バイパス素子１５を１ｍＨのオーダーで誘導巻線化すれば、リップルノイズによる磁場変動は1×10^-7のオーダーに抑えられるため、例えば、ＭＲＩ用途において実用上の問題は生じない。 The inductively wound superconducting bypass element 15 has an inductance, and the noise current is distributed between the superconducting coil 11 and the superconducting bypass element 15 with an inverse ratio of impedance between the superconducting coil 11 and the superconducting bypass element 15. become. The inductance of the superconducting coil 11 is on the order of 100H, and by configuring the inductance of the superconducting bypass element 15 on the order of 1 mH, the incorporation of ripple noise can be reduced to approximately one hundred thousandth. Ripple noise is sufficiently small compared to 1×10^-3.
Therefore, if the superconducting bypass element 15 is inductively wound on the order of 1 mH, the magnetic field fluctuation due to ripple noise can be suppressed to the order of 1×10^-7, so that no practical problem occurs in MRI applications, for example.
〔本発明の実施形態に係る超電導磁石装置の第１実装状態〕
　次に、本発明の実施形態に係る超電導磁石装置１０の第１実装状態について、図９を参照して説明する。図９は、本発明の実施形態に係る超電導磁石装置１０の第１実装状態を表す概念図である。ただし、図９に示す例では、パワーリード１７に接続される励磁電源２３、保護抵抗２５等の図示が（図３に示す例と同様のため）省略されている。 [First mounting state of superconducting magnet device according to embodiment of the present invention]
Next, a first mounting state of the superconducting magnet device 10 according to the embodiment of the present invention will be described with reference to FIG. 9. FIG. 9 is a conceptual diagram showing a first mounting state of the superconducting magnet device 10 according to the embodiment of the present invention. However, in the example shown in FIG. 9, illustrations of the excitation power source 23, protection resistor 25, etc. connected to the power lead 17 are omitted (because they are similar to the example shown in FIG. 3).
　本第１実装状態を採用した超電導磁石装置１０は、水平磁場を発生するトンネル型ＭＲＩ用の伝導冷却型超電導磁石装置である。
　超電導磁石装置１０には、図９に示すように、電動冷凍機３１が備え付けられている。電動冷凍機３１としては、例えば、２段冷凍機であるギフォード・マクマホン冷凍機（ＧＭ冷凍機）を採用することができる。この電動冷凍機（ＧＭ冷凍機）３１は、２段式で冷凍能力を発揮し、1段目（電動冷凍機３１に係る第１ステージ３３）では８０Ｋ以下に冷却することができ、２段目（電動冷凍機３１に係る第２ステージ３５）では４－１０Ｋ程度の範囲に冷却することができる。超電導磁石装置１０に備わる超電導回路１６は、電動冷凍機３１の働きによって伝導冷却された状態で運転が行われる。 The superconducting magnet device 10 employing this first mounting state is a conduction-cooled superconducting magnet device for tunnel-type MRI that generates a horizontal magnetic field.
As shown in FIG. 9, the superconducting magnet device 10 is equipped with an electric refrigerator 31. As the electric refrigerator 31, for example, a Gifford-McMahon refrigerator (GM refrigerator), which is a two-stage refrigerator, can be employed. This electric refrigerator (GM refrigerator) 31 has a two-stage cooling capacity, and the first stage (the first stage 33 related to the electric refrigerator 31) can cool down to 80K or less, and the second stage (Second stage 35 related to electric refrigerator 31) can cool to a range of about 4-10K. The superconducting circuit 16 provided in the superconducting magnet device 10 is operated in a state where it is conductively cooled by the action of the electric refrigerator 31.
　超電導回路１６に備わる超電導コイル１１、超電導バイパス素子１５等は、図３に示す例と同様に、クライオスタット１８の室内に設けられている。クライオスタット１８の室内に設けた超電導回路１６を、クライオスタット１８の室外に設けた励磁電源２３に接続するために、超電導回路１６に係る超電導性の第１導線１３は、HTSパワーリード２２を介して、常電導性（例えば燐脱酸銅製）のパワーリード１７に接続されている。 The superconducting coil 11, superconducting bypass element 15, etc. provided in the superconducting circuit 16 are provided inside the cryostat 18, as in the example shown in FIG. In order to connect the superconducting circuit 16 provided inside the room of the cryostat 18 to the excitation power source 23 provided outside the cryostat 18, the superconducting first conducting wire 13 related to the superconducting circuit 16 is connected via the HTS power lead 22. It is connected to a power lead 17 that is normally conductive (for example, made of phosphorus-deoxidized copper).
　高温超電導性のHTSパワーリード２２は、例えばREBCO、BSCCO等の銅酸化物超電導体から構成される。常電導性のパワーリード１７及び高温超電導性のHTSパワーリード２２の接続部２４（図９参照）は、電動冷凍機３１に係る第１ステージ３３にサーマルアンカーがとられている（図９中の破線矢印参照）。
　また、HTSパワーリード２２のうち低温部２６は、電動冷凍機３１に係る第２ステージ３５にサーマルアンカーがとられている（図９中の破線矢印参照）。 The high temperature superconducting HTS power lead 22 is made of a copper oxide superconductor such as REBCO or BSCCO. The connection part 24 (see FIG. 9) between the normal conductive power lead 17 and the high temperature superconducting HTS power lead 22 is thermally anchored to the first stage 33 of the electric refrigerator 31 (see FIG. 9). (see dashed arrow).
Furthermore, the low temperature section 26 of the HTS power lead 22 is thermally anchored to the second stage 35 of the electric refrigerator 31 (see the broken line arrow in FIG. 9).
　図９では図示を省略しているが、クライオスタット１８の室内には８０Ｋの輻射シールドが、超電導回路１６を含む極低温部を内包するように設けられている。この輻射シールドは、電動冷凍機３１に係る第１ステージ３３に取り付けられている。輻射シールドは、クライオスタット１８室外の輻射熱から輻射シールド内を冷却状態に保護する役割を果たす。 Although not shown in FIG. 9, an 80K radiation shield is provided inside the cryostat 18 so as to enclose the cryogenic part including the superconducting circuit 16. This radiation shield is attached to the first stage 33 of the electric refrigerator 31. The radiation shield serves to protect the interior of the radiation shield from radiant heat outside the cryostat 18 by keeping it in a cooled state.
　超電導回路１６において、超電導コイル１１及び超電導バイパス素子１５は、前記した二硼化マグネシウム（ＭｇＢ２）超電導単芯線材よりなる第１導線１３を介して超電導ループが形成されるように超電導接続されている。 In the superconducting circuit 16, the superconducting coil 11 and the superconducting bypass element 15 are superconductingly connected to form a superconducting loop via the first conducting wire 13 made of the above-described magnesium diboride (MgB 2 ) superconducting single-core wire. There is.
　本第１実装状態を採用した超電導磁石装置１０では、超電導コイル１１及び第１導線１３は、電動冷凍機３１に係る第２ステージ３５に対して高い熱伝導性を有する金属製の取付部材（不図示）を媒介して熱的に結合されている（図９中の破線矢印参照）。
　その結果、超電導コイル１１及び第１導線１３は、伝導的に冷却されている。 In the superconducting magnet device 10 adopting the present first mounting state, the superconducting coil 11 and the first conducting wire 13 are attached to the second stage 35 of the electric refrigerator 31 using a metal mounting member (non-metallic mounting member) having high thermal conductivity. (see dashed line arrow in FIG. 9).
As a result, the superconducting coil 11 and the first conducting wire 13 are conductively cooled.
　また、本第１実装状態を採用した超電導磁石装置１０に備わる超電導回路１６では、第１導線１３は、超電導コイル１１及び超電導バイパス素子１５を含んで構成される超電導ループに電流を供給すると共に、HTSパワーリード２２のうち低温部２６と、超電導ループとの間を電気的に接続している。 In addition, in the superconducting circuit 16 provided in the superconducting magnet device 10 adopting the present first mounting state, the first conducting wire 13 supplies current to the superconducting loop configured including the superconducting coil 11 and the superconducting bypass element 15, and The low temperature section 26 of the HTS power lead 22 and the superconducting loop are electrically connected.
　超電導バイパス素子１５の近傍であって、電動冷凍機３１に係る第１ステージ３３及び第２ステージ３５の間には、熱抵抗によって第１ステージ３３の温度と第２ステージ３５の温度との中間温度を生成するためのステンレス製の取付部材３７が備わっている。超電導バイパス素子１５は、この取付部材３７に熱結合された状態で設けられている。
　ただし、図９中では、取付部材３７は、電動冷凍機３１に係る第１ステージ３３及び第２ステージ３５のそれぞれに対して一体に接続される形態を例示しているが、別体の熱リンクを介して、電動冷凍機３１に係る第１ステージ３３及び第２ステージ３５のそれぞれを取付部材３７に熱結合しても構わない。 In the vicinity of the superconducting bypass element 15, between the first stage 33 and the second stage 35 of the electric refrigerator 31, an intermediate temperature between the temperature of the first stage 33 and the temperature of the second stage 35 is generated due to thermal resistance. A mounting member 37 made of stainless steel is provided for producing the same. The superconducting bypass element 15 is provided in a thermally coupled state to this mounting member 37.
However, in FIG. 9, the mounting member 37 is connected integrally to each of the first stage 33 and the second stage 35 of the electric refrigerator 31, but the mounting member 37 is a separate thermal link. Each of the first stage 33 and second stage 35 of the electric refrigerator 31 may be thermally coupled to the mounting member 37 via.
〔超電導バイパス素子１５の運転温度設定例〕
　次に、超電導バイパス素子１５に係る運転温度設定例について、図１０Ａ、図１０Ｂを参照して説明する。
　図１０Ａ、図１０Ｂは、超電導バイパス素子１５に係る運転温度設定例を表す概念図である。 [Example of operating temperature setting for superconducting bypass element 15]
Next, an example of setting the operating temperature for the superconducting bypass element 15 will be described with reference to FIGS. 10A and 10B.
10A and 10B are conceptual diagrams showing examples of operating temperature settings for the superconducting bypass element 15.
　超電導バイパス素子１５の定常状態においては、２点間の温度差と熱流の関係は電位差と電流の関係と等価である。そこで、図１０Ａ、図１０Ｂに示すように、熱抵抗を利用して、電動冷凍機３１に係る第１ステージ温度THと、電動冷凍機３１に係る第２ステージ温度TLとの温度差を分配することにより、所望の中間温度Tmを実現する。熱伝導率は温度に対して非線形性を呈する。一般に、温度が高いほど熱伝導率は大きく、熱抵抗は小さくなる。 In the steady state of the superconducting bypass element 15, the relationship between the temperature difference and heat flow between two points is equivalent to the relationship between potential difference and current. Therefore, as shown in FIGS. 10A and 10B, the temperature difference between the first stage temperature TH of the electric refrigerator 31 and the second stage temperature TL of the electric refrigerator 31 is distributed using thermal resistance. By doing so, the desired intermediate temperature Tm is achieved. Thermal conductivity exhibits nonlinearity with respect to temperature. Generally, the higher the temperature, the higher the thermal conductivity and the lower the thermal resistance.
　超電導バイパス素子１５の発熱によって生じた熱流によって、前記中間温度Tmは発熱ゼロの時と比べて前記第１ステージ温度TH側へ移動することになる。その結果、励消磁時の電流分流により動的な電流容量を小さくする効果が得られる。 Due to the heat flow generated by the heat generation of the superconducting bypass element 15, the intermediate temperature Tm moves toward the first stage temperature TH compared to when there is no heat generation. As a result, the effect of reducing the dynamic current capacity can be obtained by current shunting during excitation and demagnetization.
　基本的には、超電導バイパス素子１５に係る取付部材３７を電動冷凍機３１に係るコールドヘッド（第１ステージ３３及び第２ステージ３５）へそれぞれ接続する際の伝熱経路（第１伝熱経路及び第２伝熱経路）での熱抵抗によって、前記第１ステージ温度TH及び前記第２ステージ温度TLの温度差に基づく中間温度Tmが設定される。 Basically, the heat transfer paths (first heat transfer path and An intermediate temperature Tm based on the temperature difference between the first stage temperature TH and the second stage temperature TL is set by the thermal resistance in the second heat transfer path (second heat transfer path).
　具体的には、電動冷凍機３１の設置場所から第１ステージ３３に至る第１伝熱経路に係る熱抵抗と、電動冷凍機３１の設置場所から第２ステージ３５に至る第２伝熱経路に係る熱抵抗と、の相互作用によって、前記第１ステージ温度TH及び前記第２ステージ温度TLの温度差に基づく中間温度Tmが設定される。
　熱抵抗は材料の種別によって温度依存性が異なる。そのため、第１伝熱経路及び当該第２伝熱経路の間で熱伝導率を異なるように設定するのが好ましい。具体的には、例えば、高温側に温度依存性が大きい材料を積極的に用いることにより、励消磁時の超電導バイパス素子１５の発熱による中間温度Tmの変化を大きくとることができる。
　その結果、中間温度Tmを前記第１ステージ温度THの側へ近づけることができる。 Specifically, the thermal resistance related to the first heat transfer path from the installation location of the electric refrigerator 31 to the first stage 33, and the second heat transfer path from the installation location of the electric refrigerator 31 to the second stage 35. An intermediate temperature Tm based on the temperature difference between the first stage temperature TH and the second stage temperature TL is set by the interaction with the thermal resistance.
The temperature dependence of thermal resistance differs depending on the type of material. Therefore, it is preferable to set the thermal conductivity to be different between the first heat transfer path and the second heat transfer path. Specifically, for example, by actively using a material with high temperature dependence on the high temperature side, it is possible to increase the change in the intermediate temperature Tm due to heat generation of the superconducting bypass element 15 during excitation and demagnetization.
As a result, the intermediate temperature Tm can be brought closer to the first stage temperature TH.
〔本発明の実施形態に係る超電導磁石装置の第２実装状態〕
　次に、本発明の実施形態に係る超電導磁石装置１０の第２実装状態について、図１１を参照して説明する。図１１は、本発明の実施形態に係る超電導磁石装置１０の第２実装状態を表す概念図である。
　図９に示す超電導磁石装置１０の第１実装状態と、図１１に示す超電導磁石装置１０の第２実装状態とは、相互に共通の部分が多く存在する。そこで、これら両者の相違点について説明することで、超電導磁石装置１０の第２実装状態の説明に代えることとする。 [Second mounting state of superconducting magnet device according to embodiment of the present invention]
Next, a second mounting state of the superconducting magnet device 10 according to the embodiment of the present invention will be described with reference to FIG. 11. FIG. 11 is a conceptual diagram showing a second mounting state of the superconducting magnet device 10 according to the embodiment of the present invention.
The first mounting state of the superconducting magnet device 10 shown in FIG. 9 and the second mounting state of the superconducting magnet device 10 shown in FIG. 11 have many common parts. Therefore, the differences between the two will be explained in place of the explanation of the second mounting state of the superconducting magnet device 10.
　要するに、図９に示す超電導磁石装置１０の第１実装状態では、冷却手段として電動冷凍機３１を用いて、伝導冷却型の冷却システムを採用したのに対し、図１１に示す超電導磁石装置１０の第２実装状態では、冷却手段として冷媒を用いて、浸漬冷却型の冷却システムを採用した点で、これら両者は相違している。 In short, in the first mounting state of the superconducting magnet device 10 shown in FIG. 9, a conduction cooling type cooling system was adopted using the electric refrigerator 31 as a cooling means, whereas in the first mounting state of the superconducting magnet device 10 shown in FIG. The two are different in that the second mounting state uses a refrigerant as a cooling means and employs an immersion cooling type cooling system.
　この相違点に基づいて、第２実装状態に係る超電導磁石装置１０に備わる超電導回路１６は、図１１に示すように、液冷媒が収容された冷媒容器４１の室内に内包された状態で極低温に保持される。すなわち、超電導磁石装置１０に備わる超電導回路１６は、液冷媒によって浸漬冷却されている。
　なお、超電導コイル１１の巻線部は、その一部又は全部が液冷媒によって直接冷却されている。また、超電導バイパス素子１５は、液冷媒の液面から露出して位置している。 Based on this difference, as shown in FIG. 11, the superconducting circuit 16 provided in the superconducting magnet device 10 according to the second mounting state is kept at an extremely low temperature while being enclosed within the refrigerant container 41 containing the liquid refrigerant. is maintained. That is, the superconducting circuit 16 provided in the superconducting magnet device 10 is immersed and cooled with a liquid refrigerant.
Note that a part or all of the winding portion of the superconducting coil 11 is directly cooled by the liquid refrigerant. Moreover, the superconducting bypass element 15 is located exposed from the liquid surface of the liquid refrigerant.
　第２実装状態に係る超電導磁石装置１０では、超電導バイパス素子１５は、輻射シールド４３室内に存する冷媒容器４１の内部空間平均温度と比べて高い温度を呈する部分と熱的に結合している。 In the superconducting magnet device 10 according to the second mounting state, the superconducting bypass element 15 is thermally coupled to a portion of the refrigerant container 41 existing in the radiation shield 43 room that exhibits a higher temperature than the internal space average temperature.
　従って、第２実装状態に係る超電導磁石装置１０によれば、超電導バイパス素子１５から前記した高い温度を呈する部分に至る第１伝熱経路の熱抵抗と、超電導バイパス素子１５及び超電導コイル１１の間を電気的に接続する第１導線１３に係る熱抵抗と、に従う抵抗比によって、超電導バイパス素子１５の運転温度を設定する。 Therefore, according to the superconducting magnet device 10 in the second mounting state, the thermal resistance of the first heat transfer path from the superconducting bypass element 15 to the above-described high temperature portion and the gap between the superconducting bypass element 15 and the superconducting coil 11 The operating temperature of the superconducting bypass element 15 is set based on the thermal resistance of the first conducting wire 13 that electrically connects the superconducting bypass element 15 and the corresponding resistance ratio.
〔本発明の実施形態に係る超電導磁石装置の第３実装状態〕
　次に、本発明の実施形態に係る超電導磁石装置１０の第３実装状態について、図１２を参照して説明する。図１２は、本発明の実施形態に係る超電導磁石装置１０の第３実装状態を表す概念図である。
　図１１に示す超電導磁石装置１０の第２実装状態と、図１２に示す超電導磁石装置１０の第３実装状態とは、相互に共通の部分が多く存在する。そこで、これら両者の相違点について説明することで、超電導磁石装置１０の第３実装状態の説明に代えることとする。 [Third mounting state of superconducting magnet device according to embodiment of the present invention]
Next, a third mounting state of the superconducting magnet device 10 according to the embodiment of the present invention will be described with reference to FIG. 12. FIG. 12 is a conceptual diagram showing a third mounting state of the superconducting magnet device 10 according to the embodiment of the present invention.
The second mounting state of the superconducting magnet device 10 shown in FIG. 11 and the third mounting state of the superconducting magnet device 10 shown in FIG. 12 have many common parts. Therefore, the differences between these two will be explained in place of the explanation of the third mounting state of the superconducting magnet device 10.
　要するに、図１１に示す超電導磁石装置１０の第２実装状態では、冷却手段として冷媒を用いて超電導コイル１１を直接冷却する冷却システムを採用したのに対し、図１２に示す超電導磁石装置１０の第３実装状態では、冷却手段として冷媒を用いる点は同じであるが、冷媒を用いて超電導コイル１１を間接冷却する冷却システムを採用した点で、これら両者は相違している。 In short, in the second mounting state of the superconducting magnet device 10 shown in FIG. 11, a cooling system that directly cools the superconducting coil 11 using a refrigerant is used as a cooling means, whereas in the second mounting state of the superconducting magnet device 10 shown in FIG. The three mounting states are the same in that they use a refrigerant as a cooling means, but they are different in that they employ a cooling system that indirectly cools the superconducting coil 11 using a refrigerant.
　第３実装状態に係る超電導磁石装置１０では、輻射シールド４３室内に存する冷媒容器４１の内部空間温度と比べて高い温度を呈する部分から超電導バイパス素子１５に至る伝熱経路（図１２の破線矢印参照）の熱抵抗と、冷媒容器４１からHTSパワーリード２２のうち低温部２６に至る伝熱経路（図１２の破線矢印参照）の熱抵抗との比に従って、超電導バイパス素子１５の運転温度を、超電導コイル１１に係る雰囲気温度と比べて高く設定する。
　なお、前記高い温度を呈する部分から超電導バイパス素子１５に至る伝熱経路としては、物理的な固体熱伝導を用いた伝熱経路に限定されない。例えば、ヘリウムガスなどの気体による熱伝達を用いた伝熱経路であってもよく、また、輻射を用いた伝熱経路であっても構わない。 In the superconducting magnet device 10 according to the third mounting state, a heat transfer path (see the broken line arrow in FIG. 12 ) and the thermal resistance of the heat transfer path from the refrigerant container 41 to the low-temperature section 26 of the HTS power lead 22 (see the broken line arrow in FIG. 12), the operating temperature of the superconducting bypass element 15 is set to The temperature is set higher than the ambient temperature related to the coil 11.
Note that the heat transfer path from the high-temperature portion to the superconducting bypass element 15 is not limited to a heat transfer path using physical solid-state heat conduction. For example, it may be a heat transfer path using heat transfer by gas such as helium gas, or it may be a heat transfer path using radiation.
　従って、第３実装状態に係る超電導磁石装置１０によれば、超電導バイパス素子１５の電流容量を超電導コイル１１の電流容量に対して十分に小さくすることができる。 Therefore, according to the superconducting magnet device 10 in the third mounting state, the current capacity of the superconducting bypass element 15 can be made sufficiently smaller than the current capacity of the superconducting coil 11.
〔本発明の実施形態に係る超電導磁石装置１０を用いた核磁気共鳴診断装置７１〕
　次に、本発明の実施形態に係る超電導磁石装置１０を用いた核磁気共鳴診断装置７１について、図１３を参照して説明する。図１３は、本発明の実施形態に係る超電導磁石装置１０を用いた核磁気共鳴診断装置７１を表す説明図である。 [Nuclear magnetic resonance diagnostic device 71 using the superconducting magnet device 10 according to the embodiment of the present invention]
Next, a nuclear magnetic resonance diagnostic apparatus 71 using the superconducting magnet device 10 according to an embodiment of the present invention will be described with reference to FIG. 13. FIG. 13 is an explanatory diagram showing a nuclear magnetic resonance diagnostic apparatus 71 using the superconducting magnet device 10 according to the embodiment of the present invention.
　本発明の実施形態に係る超電導磁石装置１０を用いた核磁気共鳴診断装置７０は、核磁気共鳴現象を利用して、生体内部の状態を可視画像化して診断の用に供する装置である。 The nuclear magnetic resonance diagnostic device 70 using the superconducting magnet device 10 according to the embodiment of the present invention is a device that utilizes the nuclear magnetic resonance phenomenon to visualize the internal state of a living body and provide it for diagnosis.
　核磁気共鳴診断装置７０は、図１３に示すように、上側の超電導コイル１１と下側の超電導コイル１１とを備える超電導磁石装置１０の間隙に、被検者７１が身体を横たえるための寝台７３を搬送機７５によって進退自在に搬送するように構成されている。 As shown in FIG. 13, the nuclear magnetic resonance diagnostic apparatus 70 includes a bed 73 on which a subject 71 lies in a gap between a superconducting magnet device 10 that includes an upper superconducting coil 11 and a lower superconducting coil 11. is configured to be transported by a transporter 75 so as to be able to move forward and backward.
　本発明の実施形態に係る超電導磁石装置１０を用いた核磁気共鳴診断装置７０によれば、被検者Ｍの生体内部の状態を可視画像化して診断の用に供することができる。 According to the nuclear magnetic resonance diagnostic apparatus 70 using the superconducting magnet device 10 according to the embodiment of the present invention, the internal state of the living body of the subject M can be visualized and used for diagnosis.
　本発明に係る複数の各実施形態は、本発明を分かりやすく説明するために詳細に記載したものであって、必ずしも説明した全ての構成を備えるものに限定されない。また、実施形態の構成の一部について、他の構成の追加・削除・置換をすることが可能である。また、前記した構成は説明上必要と考えられるものを示しており、製品上必ずしも全ての構成を示しているとは限らない。 The plurality of embodiments according to the present invention are described in detail to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described. Furthermore, it is possible to add, delete, or replace some of the configurations of the embodiments with other configurations. Further, the configurations described above are those considered necessary for explanation, and do not necessarily include all configurations in terms of the product.
　なお、本発明の実施形態に係る超電導磁石装置１０の適用例として核磁気共鳴診断装置７０を例示して説明したが、本発明はこの例に限定されない。本発明の実施形態に係る超電導磁石装置１０は、時間的に安定な磁場を要求する如何なる用途に適用可能である。 Although the nuclear magnetic resonance diagnostic apparatus 70 has been described as an example of application of the superconducting magnet device 10 according to the embodiment of the present invention, the present invention is not limited to this example. The superconducting magnet device 10 according to the embodiment of the present invention can be applied to any application requiring a temporally stable magnetic field.
　１０　超電導磁石装置
　１１　超電導コイル
　１３　第１導線
　１５　超電導バイパス素子（スイッチ素子）
　１６　超電導回路
　１７、１７a、１７ｂ　パワーリード
　１８　クライオスタット（断熱真空容器）
　１９　第２導線
　２１ａ、２１ｂ　遮断スイッチ
　２３　励磁電源（電源）
　２５　保護抵抗
　３１　電動冷凍機（２段冷凍機）
　３３　第１ステージ
　３５　第２ステージ 10 superconducting magnet device 11 superconducting coil 13 first conducting wire 15 superconducting bypass element (switch element)
16 Superconducting circuit 17, 17a, 17b Power lead 18 Cryostat (insulated vacuum vessel)
19 Second conductor 21a, 21b Cutoff switch 23 Excitation power supply (power supply)
25 Protective resistance 31 Electric refrigerator (two-stage refrigerator)
33 1st stage 35 2nd stage

Claims (8)

  1. 　超電導線材が巻き回された超電導コイルと、該超電導コイルを励磁するための電源と、を備える超電導磁石装置であって、
    　前記超電導コイルには、スイッチ素子及び保護抵抗が並列に接続され、
    　前記スイッチ素子は、高温超電導体を線材として構成されており、
    　当該スイッチ素子の電流容量は、前記超電導コイルに係る定格運転電流と比べて十分に小さく、
    　当該スイッチ素子は、
    　所定の磁場を発生している際には、低抵抗状態で前記超電導コイルを電気的に短絡する一方、磁場を変化させている際には、高抵抗状態になり、前記電源から前記超電導コイルへの電流供給量を変更することで自発的に開閉状態を変えるように動作する
    　ことを特徴とする超電導磁石装置。     A superconducting magnet device comprising a superconducting coil wound with a superconducting wire and a power source for exciting the superconducting coil,
    A switch element and a protective resistor are connected in parallel to the superconducting coil,
    The switch element is configured using a high-temperature superconductor as a wire,
    The current capacity of the switch element is sufficiently small compared to the rated operating current of the superconducting coil,
    The switch element is
    When a predetermined magnetic field is being generated, the superconducting coil is electrically short-circuited in a low resistance state, while when changing the magnetic field, it is in a high resistance state and the superconducting coil is connected from the power source to the superconducting coil. A superconducting magnet device that operates to spontaneously change its open/close state by changing the amount of current supplied to the magnet.
  2. 　請求項１記載の超電導磁石装置であって、
    　前記スイッチ素子は、前記超電導コイルと超電導的に接続されて超電導回路を形成している
    　ことを特徴とする超電導磁石装置。     The superconducting magnet device according to claim 1,
    A superconducting magnet device, wherein the switch element is superconductingly connected to the superconducting coil to form a superconducting circuit.
  3. 　請求項２に記載の超電導磁石装置において、
    　前記超電導コイル及び前記スイッチ素子は、断熱真空容器に収容されており、
    　前記スイッチ素子は、断熱真空容器内のうち、前記超電導コイルの定格運転温度と比べて高い温度領域に属する場所に設けられており、
    　前記温度領域に係る温度範囲は、前記スイッチ素子の臨界温度未満であって該臨界温度に対して５Ｋ以内に設定される
    　ことを特徴とする超電導磁石装置。     The superconducting magnet device according to claim 2,
    The superconducting coil and the switch element are housed in an insulated vacuum container,
    The switch element is provided in a location within the insulated vacuum container that belongs to a temperature range higher than the rated operating temperature of the superconducting coil,
    A superconducting magnet device, wherein a temperature range related to the temperature region is set to be less than a critical temperature of the switching element and within 5K with respect to the critical temperature.
  4. 　請求項３記載の超電導磁石装置であって、
    　前記断熱真空容器の室内は冷媒を用いて冷却されており、
    　前記スイッチ素子は、前記断熱真空容器の内部空間平均温度と比べて高い温度を呈する部分と熱的に結合しており、前記スイッチ素子から前記高い温度を呈する部分に至る伝熱経路の熱抵抗と、当該スイッチ素子及び前記超電導コイルの間を電気的に接続する第１導線に係る熱抵抗と、に従う抵抗比によって、当該スイッチ素子の運転温度を設定する
    　ことを特徴とする超電導磁石装置。     The superconducting magnet device according to claim 3,
    The interior of the insulated vacuum container is cooled using a refrigerant,
    The switch element is thermally coupled to a portion exhibiting a higher temperature than the average internal temperature of the insulating vacuum container, and has a thermal resistance of a heat transfer path from the switch element to the portion exhibiting the high temperature. , and a thermal resistance of a first conducting wire electrically connecting between the switch element and the superconducting coil, and an operating temperature of the switch element is set by a resistance ratio according to the following.
  5. 　請求項３記載の超電導磁石装置であって、
    　前記断熱真空容器の室内は、相互に冷凍能力の異なる第１ステージ及び第２ステージが備わる２段冷凍機を用いて冷却されており、
    　前記スイッチ素子は、前記２段冷凍機に熱的に結合された所定の設置場所に設けられており、当該スイッチ素子に係る設置場所から前記第１ステージに至る第１伝熱経路に係る熱抵抗と、当該スイッチ素子に係る設置場所から前記第２ステージに至る第２伝熱経路に係る熱抵抗と、に差をつけることで中間温度を設定する
    　ことを特徴とする超電導磁石装置。     The superconducting magnet device according to claim 3,
    The interior of the insulated vacuum container is cooled using a two-stage refrigerator equipped with a first stage and a second stage having mutually different refrigerating capacities,
    The switch element is provided at a predetermined installation location that is thermally coupled to the two-stage refrigerator, and has a thermal resistance associated with a first heat transfer path from the installation location of the switch element to the first stage. and a thermal resistance related to a second heat transfer path from the installation location of the switch element to the second stage to set an intermediate temperature.
  6. 　請求項５記載の超電導磁石装置であって、
    　前記スイッチ素子は、２段冷凍機に係る第１ステージ及び第２ステージに熱的に結合されたステージに設けられており、前記第１伝熱経路に係る熱抵抗と、前記第２伝熱経路に係る熱抵抗との温度依存性に差をつけるために、当該第１伝熱経路及び当該第２伝熱経路の間で熱伝導率を異なるように設定した
    　ことを特徴とする超電導磁石装置。     The superconducting magnet device according to claim 5,
    The switch element is provided on a stage that is thermally coupled to a first stage and a second stage of the two-stage refrigerator, and has a thermal resistance related to the first heat transfer path and a heat transfer path related to the second heat transfer path. A superconducting magnet device characterized in that the thermal conductivity is set to be different between the first heat transfer path and the second heat transfer path in order to differentiate the temperature dependence with respect to the thermal resistance.
  7. 　請求４又は５に記載の超電導磁石装置であって、
    　前記スイッチ素子のオフ状態における電気抵抗の値は、前記保護抵抗の電気抵抗の値と比べて１０倍以上に設定される
    　ことを特徴とする超電導磁石装置。     The superconducting magnet device according to claim 4 or 5,
    A superconducting magnet device, wherein an electrical resistance value of the switch element in an off state is set to be ten times or more greater than an electrical resistance value of the protective resistor.
  8. 　請求４又は５に記載の超電導磁石装置を用いた核磁気共鳴診断装置。 A nuclear magnetic resonance diagnostic device using the superconducting magnet device according to claim 4 or 5.
PCT/JP2023/028156 2022-09-02 2023-08-01 Superconducting magnet device and nuclear magnetic resonance diagnosis device WO2024048179A1 (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH10294213A (en) * 1997-04-22 1998-11-04 Hitachi Ltd Manufacture for oxide based superconducting magnet system and oxide based superconducting magnet system and superconducting magnetic field generation apparatus
JP2009273673A (en) * 2008-05-15 2009-11-26 Mitsubishi Electric Corp Superconducting electromagnet and mri apparatus
JP2020068293A (en) * 2018-10-24 2020-04-30 株式会社東芝 Superconducting magnet device

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH10294213A (en) * 1997-04-22 1998-11-04 Hitachi Ltd Manufacture for oxide based superconducting magnet system and oxide based superconducting magnet system and superconducting magnetic field generation apparatus
JP2009273673A (en) * 2008-05-15 2009-11-26 Mitsubishi Electric Corp Superconducting electromagnet and mri apparatus
JP2020068293A (en) * 2018-10-24 2020-04-30 株式会社東芝 Superconducting magnet device

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