CN115515292B - Proton injector - Google Patents

Abstract

The invention relates to a proton injector, which comprises an ion source, a low-energy transmission line, a radio-frequency quadrupole accelerator, an interdigital magnetic drift tube linear accelerator, a medium-energy transmission line and a beam splitter which are connected in sequence, wherein a first matching section is arranged between the radio-frequency quadrupole accelerator and the interdigital magnetic drift tube; the radio-frequency quadrupole accelerator comprises a first cavity, wherein the first cavity is provided with four electrodes; the interdigital magnetic drift tube linear accelerator comprises a second cavity, a third cavity and a second matching section, wherein the second cavity comprises a second beam focusing section and a second accelerating section, and the third cavity comprises a third beam focusing section and a third accelerating section; when the proton beam enters the interdigital magnetic drift tube linear accelerator, it passes through the second beam segment with a first beam-focusing phase and passes through the third beam segment with a second beam-focusing phase that is smaller than the first beam-focusing phase. The invention also includes a tuner comprising a tuning body, a tuning nut, a screw, and a tuning rod. The invention can improve the beam quality and realize more accurate tuning.

Description

Proton injector

Technical Field

The invention relates to the technical field of particle accelerators, in particular to a proton injector designed based on an oligomerization beam phase and an integrated interdigital magnetic type drift tube linear accelerator (IH-DTL).

Background

Proton accelerators are used in a wide variety of medical applications, such as proton therapy, boron Neutron Capture Therapy (BNCT), medical isotope production, and the like. However, protons with low energy have the characteristics of low speed and strong space charge effect, and the conventional accelerator can cause poor beam quality, so that some special accelerating structures are needed. For proton therapy, where higher energy is required, a low energy accelerator is used to accelerate and inject the beam into the main accelerator, also known as an injector. The energy of the proton after acceleration of the injector is improved, the speed is greatly improved, the space charge effect is weakened, and the beam quality is easy to control in the subsequent acceleration process, so that the quality of the injector determines the quality of the whole accelerator system to a great extent.

The proton implanter is mainly composed of an ion source, a low energy transmission line, a radio frequency quadrupole accelerator (RFQ, radio Frequency Quadruple), a drift tube linac (DTL, drifting Tube Linac), a medium energy transmission line and a beam splitter. Wherein, DTL is an accelerator structure composed of a drift tube and an acceleration gap, and is an optimum accelerator type at proton speeds β to 0.1. The traditional DTL type, namely the Alvarez type DTL, has lower acceleration gradient and longer acceleration energy length. In addition, the DTL needs to be added with permanent magnetic quadrupole iron in the drift tube, so that the process difficulty is high, the possible error is large, and the adjustment is difficult after the processing is finished.

To solve the above problems, the prior art has developed a new DTL type, an interdigital magnetic drift tube linac (IH-DTL). The IH-DTL has the advantages that the acceleration gradient is high, the length of the DTL can be greatly reduced, meanwhile, the magnet does not need to be arranged in the drift tube, the process difficulty is reduced, the selection range of the magnet is wider, electromagnetic quadrupole iron can be selected, and the magnet can be adjusted aiming at errors in the actual debugging and running processes. The IH-DTL has two different designs, one of which is APF (ALTERNATING PHASE Focusing, alternate phase focusing) beam hydrodynamic design, the inlet acceptance of the IH-DTL of the scheme is lower, the requirements on processing errors and operation stability are extremely high, and once the inlet beam parameters deviate or have errors in structure, the outlet beam parameters generate extremely large errors and cannot meet the requirements. Another design of IH-DTL is KONUS (Kombinierte Null Grad Struktur) beam hydrodynamic design, which overcomes the drawbacks of APF scheme, but its bunching effect in proton injectors is poor, resulting in poor beam quality.

In addition, because the machine may experience various errors during machining, assembly, welding, etc., the cavity needs to be tuned to achieve an optimal condition. In proton injectors, the prior art generally uses a tuning rod for tuning. The tuning rod is inserted into the cavity through the hole on the cavity wall, and the microwave performance of the cavity is changed by controlling the insertion depth of the tuning rod, so that the tuning purpose is realized. The existing scheme is to process a tuning rod with a certain length, calculate the required insertion depth of the tuning rod through tuning experiments, and calculate the length of the tuning rod outside the cavity. After several iterative experiments, final parameters are determined and the tuning rod is cut to the desired length. This tuning method is less accurate and less repeatable, different person measurements can produce different errors, and errors in the tuning process are difficult to compensate because the tuning rod eventually needs to be cut.

Disclosure of Invention

In order to solve the above problems in the prior art, the present invention provides a proton injector, which adopts an oligomerization beam phase and an integrated IH-DTL design, and can improve beam quality and realize more accurate tuning.

The invention provides a proton injector, which comprises an ion source, a low-energy transmission line, a radio-frequency quadrupole accelerator, an interdigital magnetic drift tube linear accelerator, a medium-energy transmission line and a beam splitter which are sequentially connected, wherein a first matching section is arranged between the radio-frequency quadrupole accelerator and the interdigital magnetic drift tube; the radio-frequency quadrupole accelerator comprises a first cavity, wherein the first cavity is provided with four electrodes; the interdigital magnetic drift tube linear accelerator comprises a second cavity, a third cavity and a second matching section connected with the second cavity and the third cavity, wherein the second cavity comprises a second beam focusing section and a second accelerating section along the direction of proton beam, and the third cavity comprises a third beam focusing section and a third accelerating section along the direction of proton beam; when a proton beam enters the interdigital magnetic type drift tube linear accelerator, the proton beam passes through the second beam section with a first beam focusing phase and passes through the third beam section with a second beam focusing phase smaller than the first beam focusing phase.

Preferably, the first matching section is composed of a plurality of electromagnetic quadrupoles.

Preferably, the second matching section is composed of a plurality of electromagnetic quadrupoles.

Preferably, the first beam converging phase is-35 ° and the second beam converging phase is-60 °.

Preferably, the second cavity, the third cavity and the second matching section are of an integrated design.

Further, tuners are arranged on the first cavity, the second cavity and the third cavity.

Further, the tuner comprises a tuning main body, a tuning nut arranged on the tuning main body, a screw rod movably connected with the tuning nut and a tuning rod connected with the screw rod.

Further, the tuning body is fixed on the outer wall of the first cavity, the second cavity and/or the third cavity.

Further, the tuning rod extends out from the bottom of the tuning body and is inserted into the first cavity, the second cavity and/or the third cavity through the openings on the first cavity, the second cavity and/or the third cavity.

Further, the first cavity, the second cavity and the third cavity are all fed with power through a magnetic coupler.

According to the proton injector, through the two-cavity integrated design of IH-DTL, the speed and the precision of cavity collimation can be improved, so that the cavity is more stable and the operation is more stable. The optimized IH-DTL parameter design can realize shorter length and smaller outlet beam energy dispersion, and improves the beam quality. In addition, the invention adopts the design of the tuner capable of reciprocating and having higher precision, can precisely control the depth of the tuning rod entering the cavity, and realizes more precise tuning of the frequency and the field distribution of the cavity.

Drawings

Fig. 1 is a schematic structural view of a proton injector according to the present invention.

Fig. 2 is a schematic diagram of the structure of the ion source of fig. 1.

Fig. 3 (a) and 3 (b) are schematic structural views of the rf quadrupole accelerator of fig. 1.

Fig. 4 is a schematic diagram of the structure of the interdigital drift tube linac of fig. 1.

Fig. 5 is a schematic structural diagram of a tuner.

Detailed Description

Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As shown in fig. 1, the proton injector provided by the invention comprises an ion source 1, a low energy transmission line 2 (LEBT), a radio frequency quadrupole accelerator 3 (RFQ), an interdigital magnetic drift tube linac 4 (IH-DTL), a medium energy transmission line 5 and a beam splitter 6 which are connected in sequence. Since the phase space distribution of the proton beam at the RFQ outlet is opposite to the horizontal direction and the vertical direction, the injection requirement of IH-DTL cannot be satisfied, and therefore, the first matching section 31 is provided between the RFQ and the IH-DTL.

The ion source 1 is used for generating proton beam current, and is a source of the whole system. As shown in fig. 2, the ion source 1 includes a gas injection port 11 for introducing hydrogen gas, and a microwave input port 12 for feeding microwave power. The principle of generating proton beam current is: the hydrogen gas is ionized to form plasma at the electrode position, and protons are separated and extracted by using the extraction high pressure. In the present invention, the ion source 1 employs an Electron Cyclotron Resonance (ECR) type ion source to avoid the dual plasma (Duoplasmatron) type ion source filament escaping gaseous impurities to contaminate the chamber.

The low-energy transmission line 2 is used for transmitting the proton beam generated by the ion source 1 and focusing the proton beam so that the proton beam can meet the emittance requirement of the entrance of the radio-frequency quadrupole accelerator 3. The low energy transmission line 2 may be considered as an integral part of the ion source system along with the ion source 1.

The rf quadrupole accelerator 3 is configured to receive the proton beam transmitted and focused through the low energy transmission line 2 and accelerate the proton beam to a desired preset energy. The radio-frequency quadrupole accelerator 3 mainly generates stronger focusing effect by four electrodes, solves the problem of the increase of the emittance of proton beam current under low energy, and simultaneously adds modulation on the polar head to generate acceleration effect. Specifically, the rf quadrupole accelerator 3 comprises a first cavity with four electrodes, and the angle between two adjacent electrodes is 90 °. The electrode tips are modulated to form a trigonometric-like shape, and as shown in fig. 3 (a), the two opposing tips are symmetrical in shape, the modulation gradually increases from the inlet to the outlet, and the amplitude of the corresponding curve increases. Whereas the shapes of two adjacent poles are opposite (the trigonometric functions differ by 180 °), as shown in fig. 3 (b), the shading in the figure indicates the cross section of four poles, the diagonal lines in the first quadrant indicate the longitudinal section of the poles (i.e. the two are half poles to represent the pole curves), and the curve indicates the pole shape (at the same position, one pole is convex and the other pole is concave). In the cavity, an electric quadrupolar field is formed because of the four pole tips, and a longitudinal electric field is formed because of trigonometric-like modulation of the pole tips.

In the invention, the radio-frequency quadrupole accelerator 3 is of a four-wing type, can keep better performance at high frequency, and has easy cooling of the pole head. According to the characteristic of RFQ pole head modulation, the radio-frequency quadrupole accelerator 3 sequentially comprises a radial matching section, a forming section, a first beam focusing section and a first accelerating section along the trend of proton beam. In the radial matching section, the focusing force increases from 0 to a maximum value over a short distance, the proton beam current being adapted here nondestructively to the focusing force which varies over time; in the forming section, the synchronous phase is increased from-90 degrees, the longitudinal electric field is increased from 0, and the preparation is preliminarily made for shaping the beam shape and bunching; in the first beaming segment, the synchronization phase is further modulated to a final value; in the first acceleration section, the synchronous phase is not changed any more, and the polar modulation is further increased, so that the acceleration efficiency is improved, and the proton beam is accelerated to the finally required energy.

The rf quadrupole accelerator 3 uses a magnetic coupler to feed power, and its principle is: radio frequency power is generated from a power source, transmitted to the magnetic coupler through the coaxial cable, and then excites an electromagnetic field in the cavity through the annular probe of the magnetic coupler.

The first matching section 31 is used for connecting the rf quadrupole accelerator 3 and the interdigital magnetic type drift tube linac 4, and has the function of converting the transverse shape of the proton beam at the outlet of the rf quadrupole accelerator 3 into the shape required by the interdigital magnetic type drift tube linac 4. The first matching section 31 is composed of a plurality of electromagnetic quadrupoles, and the flexible adjustment capability of the first matching section can cope with errors possibly generated by factors such as processing, operation, environment and the like, so that the proton beam is ensured to be in a stable and good state.

As shown in fig. 4, the interdigital magnetic type drift tube linac 4 comprises a second cavity 41 and a third cavity 42, each of which is a structure in which drift tubes 44 are alternately connected to a cavity wall 46 through support rods 45, and are 180 ° in cross section, and the center of the drift tube, the center of the cavity and the beam track are coincident. Wherein the second cavity 41 comprises a second beam section for changing the shape of the proton beam and a second acceleration section for acceleration along the proton beam direction, and the third cavity 42 comprises a third beam section and a third acceleration section along the proton beam direction. When the proton beam enters the interdigital magnetic drift tube linac 4, it passes through the second beam segment with a first beam-condensing phase and through the third beam segment with a second beam-condensing phase that is smaller than the first beam-condensing phase.

After acceleration of the proton beam stream through the second cavity 41, the movement trend in both the horizontal and vertical directions becomes defocused, so that a second matching section 43 is provided between the second cavity 41 and the third cavity 42 to change the phase space distribution of the proton beam stream. Like the first matching section 31, the second matching section 43 is composed of several electromagnetic quadrupoles to ensure a better focusing effect. After focusing and adjusting by the second matching section 43, the movement trend of the proton beam in the horizontal and vertical directions returns to focusing.

In the present invention, the first beam-condensing phase is typically-35 ° and the second beam-condensing phase is about-60 °. Because the second beam converging phase adopts a phase lower than the classical phase, the final energy dispersion of the beam can be effectively reduced, the particle number which can be injected into a subsequent accelerating structure is improved, a better beam converging effect is realized, and the beam quality is improved.

In addition, the second cavity 41, the third cavity 42 and the second matching section 43 are integrally designed. The integrated design can enable collimation between two cavities of the IH-DTL to be more convenient and accurate, reduce position errors of the cavities, and strengthen the machine and enable operation of the accelerator to be more stable.

The second cavity 41 and the third cavity 42 are two independent complete cavities, and are fed with power by two magnetic couplers respectively. The design can lead the length of the second matching section 43 not to be limited by the synchronous phase requirement of the beam, improves the flexibility of the second matching section 43, shortens the cavity length at the same time, is beneficial to designing the matching section with reasonable magnet gradient and layout and shorter total length, and can provide convenience for the power supply of the electromagnet.

The medium energy transmission section 5 is used for transmitting and focusing the proton beam after being accelerated by the interdigital magnetic type drift tube linear accelerator 4 so as to avoid the overlarge increase of the emittance of the proton beam in long-distance drift. In the medium energy transmission section 5, the beam energy is relatively high, the emittance is relatively slow to increase in the transmission process, and the beam is not accelerated, so that the requirement on errors is low, and real-time adjustment is not needed for actual running conditions. Thus, the intermediate energy transmission section 5 of the present invention uses permanent magnet quadrupoles.

The beam splitter 6 is the last part of the whole proton injector and is used for further reducing the energy dispersion of the proton beam, so as to ensure that more beam can enter the subsequent accelerator. The beam splitter 6 can be selected according to the actual situation.

For tuning, a tuner 7 is disposed on the first cavity of the rf quadrupole accelerator 3, and on the second cavity 41 and the third cavity 42 of the interdigital magnetic type drift tube linac 4. As shown in fig. 5, the tuner 7 includes a tuning body 71, a tuning nut 72 provided on the tuning body 71, a screw 73 movably connected to the tuning nut 72, and a tuning rod 74 connected to the screw 73. Wherein the tuning body 71 is fixed on the outer wall of the first, second and/or third cavities 41, 42, and the tuning rod 74 extends from the bottom of the tuning body 71 and is inserted into the cavity through an opening in the cavity. When the cavity is tuned, the tuning nut 72 is utilized to adjust the screw 73, and the screw 73 drives the tuning rod 74 to move so as to adjust the depth of the tuning rod 74 inserted into the cavity. The tuner of the invention can accurately control the insertion depth of the tuning rod through a mechanical structure, can realize reciprocating adjustment, and realizes high-precision tuning by utilizing a screw rod with small pitch. The tuner of the invention can better tune the cavity, so that the field distribution error is reduced to be lower, and the better result than the existing tuning mode is achieved.

The principle of operation of the proton injector of the present invention is further described below by way of a specific example for ease of understanding.

The ion source 1 adopts a compact 2.45GHz ECR ion source with an all-permanent magnet structure, and hydrogen is introduced into the ion source 1 through the gas injection port 11 and the microwave input port 13 respectively and microwave power is fed in. The hydrogen formed a plasma at the electrode location, and the protons were separated and extracted using an extraction high pressure, with an extraction energy of 30keV. The low energy transmission line 2 focuses the protons while transmitting, after which the protons leave the ion source system and enter the RFQ in a continuous beam.

The proton beam first enters the radial matching section of the RFQ where the aperture of the accelerator is rapidly reduced, modulating the lateral shape of the beam to enter the acceptance range. In the shaping section, the modulation of the pole head is gradually increased from 0, and the continuous beam current is also gradually gathered into clusters. In the first beam focusing section, the modulation of the polar head is further increased to the maximum value, the beam is further focused into clusters, and the transverse and longitudinal phase space distribution of the clusters vibrate periodically. The final beam enters a first acceleration stage in which the pole tip remains substantially unchanged at maximum modulation. The beam is accelerated to be more than 3.5MeV within the length of 3 meters through RFQ, and the transmission efficiency is more than 80%.

After passing through the first matching section 31 composed of three electromagnetic quadrupoles, the beam current becomes uniform in phase space distribution, and the motion trend is focused and enters IH-DTL. After entering IH-DTL, the beam first enters the second beam segment. Since the first matching section 31 focuses the beam, the length of the beam becomes long, and thus the second focusing beam Duan Xian is required to compress the length of the beam. The second beam converging section of the second cavity 42 is provided with 3 accelerating units with a synchronization phase of-35 degrees, the beam enters the second accelerating section after being converged, and the length of the beam is longer at the moment, so that the beam is compressed to the desired length after being accelerated by three units by using the synchronization phase of-60 degrees in the third beam converging section of the third cavity 43. After passing through the third acceleration section of the third cavity 43, the beam energy reaches above 7 MeV.

The accelerator section of the whole proton injector ends up, but a medium energy transmission line 5 is often required for the subsequent beam to be transmitted from the injector to the subsequent accelerator. Long-distance drift of the beam causes an increasing lateral dimension, so that the beam is focused mainly by quadrupole iron in the MEBT to ensure that the beam maintains better quality in the long-distance transmission process. Following the MEBT is a beam splitter 6 for re-beaming the beam to a continuous beam state while further reducing beam energy dispersion. After passing through the beam splitter 6, most of the beam current is in the energy range of-0.3 MeV to 0.1MeV, and the beam current within the energy range of +/-50 keV can be more than 80% of the input beam current. For example, where the input beam intensity of the entire injector is 18A, the beam intensity in the range of 50keV can be greater than 14.4A. The invention can meet the injection requirements of most medical accelerators.

The foregoing description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention, and various modifications can be made to the above-described embodiment of the present invention. All simple, equivalent changes and modifications made in accordance with the claims and the specification of this application fall within the scope of the patent claims. The present invention is not described in detail in the conventional art.

Claims (10)

1. The proton injector is characterized by comprising an ion source, a low-energy transmission line, a radio-frequency quadrupole accelerator, an interdigital magnetic drift tube linear accelerator, a medium-energy transmission line and a beam splitter which are connected in sequence, wherein a first matching section is arranged between the radio-frequency quadrupole accelerator and the interdigital magnetic drift tube; wherein,

The radio-frequency quadrupole accelerator comprises a first cavity, wherein the first cavity is provided with four electrodes;

The interdigital magnetic drift tube linear accelerator comprises a second cavity, a third cavity and a second matching section connected with the second cavity and the third cavity, wherein the second cavity comprises a second beam focusing section and a second accelerating section along the direction of proton beam, and the third cavity comprises a third beam focusing section and a third accelerating section along the direction of proton beam; when a proton beam enters the interdigital magnetic type drift tube linear accelerator, the proton beam passes through the second beam section with a first beam focusing phase and passes through the third beam section with a second beam focusing phase smaller than the first beam focusing phase.

2. The proton injector as recited in claim 1, wherein the first matching section is comprised of a plurality of electromagnetic quadrupoles.

3. The proton injector as recited in claim 1, wherein the second matching section is comprised of a plurality of electromagnetic quadrupoles.

4. Proton injector according to claim 1, characterized in that the first beam-converging phase is-35 ° and the second beam-converging phase is-60 °.

5. The proton injector as recited in claim 1, wherein the second cavity, the third cavity, and the second mating section are of an integrated design.

6. The proton injector as recited in claim 1, wherein tuners are provided on each of the first chamber, the second chamber, and the third chamber.

7. The proton injector as recited in claim 6, wherein the tuner includes a tuning body, a tuning nut disposed on the tuning body, a threaded rod movably coupled to the tuning nut, and a tuning rod coupled to the threaded rod.

8. Proton injector according to claim 7, characterized in that the tuning body is fixed on the outer wall of the first, second and/or third cavity.

9. Proton injector according to claim 7, characterized in that the tuning rod protrudes from the bottom of the tuning body and is inserted into the interior of the first, second and/or third cavity through an opening in the first, second and/or third cavity.

10. The proton injector as recited in claim 1, wherein the first cavity, the second cavity, and the third cavity are all fed power through a magnetic coupler.