CN109100567B - Method for testing modulation frequency of synchrocyclotron - Google Patents
Method for testing modulation frequency of synchrocyclotron Download PDFInfo
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- CN109100567B CN109100567B CN201810686061.6A CN201810686061A CN109100567B CN 109100567 B CN109100567 B CN 109100567B CN 201810686061 A CN201810686061 A CN 201810686061A CN 109100567 B CN109100567 B CN 109100567B
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Abstract
The invention discloses a method for testing the modulation frequency of a synchrocyclotron, which relates to the technical field of synchrocyclotron and comprises the following steps: selecting the movement mode of the rotating capacitor as a position mode, setting the circumferential movement with a fixed stepping angle, and performing frequency scanning on the cavity of the synchrocyclotronObtaining the cavity eigenfrequency interval f1～f2(ii) a Selecting a frequency value f of the cavity eigenfrequency0Stopping rotating the capacitor driver; adjusting the cavity coupling capacitance so as to be at f0S parameter of chamber11Less than-15 dB; setting the signal source frequency to f0The power is 10dBm, the continuous mode is adopted, the output signal of the continuous mode is connected to the coupling end of the cavity, and the cavity capacitance sampling signal is connected to the oscilloscope; selecting a motion mode of the rotating capacitor as a speed mode, and increasing the rotating speed of the rotating capacitor to a designed rotating speed; and testing the time interval delta X between the peaks of the sampling cavity capacitance sampling signal by using an oscilloscope, wherein 1/delta X is the modulation frequency of the synchrocyclotron.
Description
Technical Field
The invention relates to the technical field of synchrocyclotron, in particular to a method for testing modulation frequency of a synchrocyclotron.
Background
A cyclotron is a device that uses a magnetic field and an electric field to cause charged particles to make a cyclotron motion together, and repeatedly accelerates the charged particles in the motion by a high-frequency electric field, and is an important instrument in high-energy physics.
The current cyclotron has the main structure that two semicircular metal flat boxes (D-shaped boxes) are arranged in a vacuum chamber between magnetic poles in a spaced and opposite mode, alternating voltage is applied to the D-shaped boxes, and an alternating electric field is generated at a gap between the D-shaped boxes. The particle source arranged in the center generates charged particles to be ejected, the charged particles are accelerated by an electric field, and the charged particles do circular motion in a vertical magnetic field plane only by Lorentz force of a magnetic field between magnetic poles without electric field force in the D-shaped box. The time of the half-turn is pi m/qB, wherein the parameter q is the charge of the particles, m is the mass of the particles, and B is the magnetic induction intensity of the magnetic field. If the frequency of the alternating voltage applied to the D-shaped box is exactly equal to the frequency of the particles making circular motion in the magnetic field, the particles just catch up with the voltage direction change on the D-shaped box after half a turn, and the particles are still in an acceleration state. Since the time for the particles to make a half turn is independent of the velocity of the particles, the particles are accelerated once per half turn, and the turn radius increases. After many accelerations, the particles are drawn out from the edge of the D-shaped box along a spiral track, and the energy can reach dozens of MeV. However, as the particle velocity increases, the mass of the particles increases according to the relativistic effect, and the detour period of the particles becomes longer, thereby gradually deviating from the acceleration state of the alternating electric field. To solve the above problems, synchrocyclotron operation has been developed.
Synchrocyclotron (synchrocyclotron) is a cyclotron, also called a phase-stabilized accelerator or a frequency-modulated cyclotron, developed to overcome the limit energy of the above-mentioned classical cyclotron. The method is mainly different from the classical cyclotron in that a frequency modulation technology is adopted, so that the frequency of a cavity (a cavity where an accelerating electric field is located) is synchronously reduced along with the cyclotron frequency of particles in the process of accelerating the particles, the resonance acceleration condition is kept, and the limitation of relativistic mass increase in the classical cyclotron on energy improvement is broken through.
In the application of the synchrocyclotron, after a certain particle beam is led out, the cavity frequency is quickly adjusted back to the initial acceleration frequency, and the acceleration of the next beam group is continued. The time corresponding to the periodic acceleration of the ions is the modulation time, and the inverse is the modulation frequency. The variation of the cavity frequency of the synchrocyclotron is generally achieved by a periodic rotating capacitor. Based on the above description, it can be seen that, in the control of the synchrocyclotron, the precise application of the frequency modulation technology corresponding to the cavity frequency can greatly improve the performance of the synchrocyclotron, and thus, the test of the modulation frequency of the synchrocyclotron is very important. Currently, the modulation frequency is usually measured indirectly by a resonant loop parameter test or the like, and the cavity eigen frequency interferes with a test result in the test process, so that the test result has a large error.
Disclosure of Invention
Aiming at the defects in practical application, the invention aims to provide a method for testing the modulation frequency of a synchrocyclotron, which can realize direct test on the modulation frequency so as to verify whether the modulation frequency meets the design requirements of the synchrocyclotron, and the specific scheme is as follows:
a method for testing modulation frequency of a synchrocyclotron is based on the fact that a periodic rotating capacitor and a rotating capacitor driver are arranged in a cavity of the synchrocyclotron, the rotating capacitor comprises rotating capacitor rotor blades and rotating capacitor stator blades, and the method comprises the following steps:
1) selecting a motion mode of a rotating capacitor as a position mode, setting circumferential motion with a stepping angle of 0.5-2 degrees, setting time at an interval between two adjacent motions, and simultaneously performing S-parameter frequency scanning on a cavity of the synchrocyclotron by using a network analyzer to obtain the whole eigenfrequency interval of the cavity, which is recorded as f 1-f 2;
2) selecting a frequency value f0 which is close to the middle frequency in the cavity eigenfrequency range f 1-f 2, and stopping rotating the capacitor driver;
3) adjusting the cavity coupling capacitance such that S11 is less than-15 dB in the S parameter of the cavity at f 0;
4) setting the frequency of a signal source to be f0 and the power to be 10dBm, connecting an output signal of the signal source to a coupling end of a cavity, connecting a cavity capacitance sampling signal to an oscilloscope, vacuumizing a rotating capacitance vacuum chamber, wherein the vacuum degree of the rotating capacitance vacuum chamber is not higher than 0.1 mbar;
5) selecting a motion mode of the rotating capacitor as a speed mode, and stably increasing the rotating speed of the rotating capacitor to a designed rotating speed;
6) and testing the time interval delta x and the reciprocal 1/delta x between the peaks of the sampling cavity capacitance sampling signal by utilizing the scale function of the oscilloscope, wherein 1/delta x is the modulation frequency of the synchrocyclotron.
Further, in the step 1), the time interval between two adjacent movements of the rotating capacitor rotor blade is set to be a fixed value of 4-6 s.
Further, in the step 4), the internal resistance of the input signal port of the oscilloscope is set to be 50 ohms.
Further, in the step 5), the acceleration of the rotating capacitor is 40-70 rpm/s.
Compared with the prior art, the invention has the following beneficial effects:
by detecting the cavity eigenfrequency and adjusting the cavity coupling capacitance, the influence of the cavity eigenfrequency on the measurement result is reduced, and the accuracy of the directly measured modulation frequency result is ensured.
Drawings
FIG. 1 is a schematic diagram of a cavity structure of a synchrocyclotron according to the present invention;
FIG. 2 is a schematic diagram illustrating the steps of the method for testing the modulation frequency of the synchrocyclotron according to the present invention;
FIG. 3 is a layout diagram of a synchrocyclotron modulation frequency test;
fig. 4 is a graph of a synchrocyclotron modulation frequency test.
Reference numerals: 1. a coupling end; 2. a coupling capacitor; 3. a Dee plate; 4. a main vacuum chamber; 5. a short-circuit terminal; 6. rotating the capacitor vacuum chamber; 7. rotating the capacitive stator; 8. rotating the capacitive rotor; 9. a rotating shaft.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited to these examples.
As shown in fig. 1, a schematic diagram of a cavity structure of a synchrocyclotron is shown, and a half-wavelength structure is adopted, a head part is provided with a coupling end 1, a Dee plate 3 and a main vacuum chamber 4, a coupling capacitor 2 is formed between the coupling end 1 and the Dee plate 3, and a rotating capacitor at a tail part and a rotating capacitor vacuum chamber 6 thereof are connected through a transmission line. The tail part rotating capacitor stator 7 blades are two layers, the rotating capacitor rotor 8 blades are one layer, the rotating capacitor rotor 8 blades are in transmission connection with a rotating capacitor driver through a rotating shaft 9, the rotating capacitor stator 7 blades and the rotating capacitor rotor 8 blades have set axial distance, the change of the equivalent capacitance of the cavity is completed through the rotation of the rotating capacitor rotor 8 blades, and then the modulation of the cavity frequency is realized. In a practical case, the head high-voltage terminal and the tail high-voltage terminal of the Dee plate 3 in the cyclotron are connected through a transmission line.
As shown in fig. 3, which is a layout diagram for testing modulation frequency of a synchrocyclotron, a rotating shaft 9 is connected with a rotating capacitor driver, and the rotating capacitor driver includes a motor, and the motor is connected with the motor driver and a control terminal. The rotary capacitor vacuum chamber 6 is connected with a vacuum pump through a corrugated pipe to realize the vacuum of the rotary capacitor vacuum chamber 6. The signal source and the oscilloscope are both connected with the cavity through transmission lines.
As shown in fig. 1, the synchrocyclotron further includes a short-circuit end 5 (inner rod), the short-circuit end 5 is disposed at a position where an electric field is weak, the short-circuit end 5 may be equivalent to an inductor, and if the short-circuit end 5 increases corresponding to an increase in inductance, the resonant frequency of a resonant circuit formed by the short-circuit end and the rotating capacitor decreases, and otherwise, if the short-circuit end 5 decreases in length corresponding to a decrease in inductance, the resonant frequency increases.
Based on the structure of the synchrocyclotron, as shown in fig. 2, the modulation frequency testing method of the present invention includes the following steps:
1) selecting a motion mode of a rotating capacitor as a position mode, setting circumferential motion with a stepping angle of 0.5-2 degrees, preferably 1 degree, setting time for two adjacent motion intervals, setting the time as a fixed value of 4-6S, preferably 5S, and simultaneously carrying out frequency scanning on S parameters (the S parameters are network parameters established on the basis of incident wave and reflected wave relations) on a cavity of the synchrocyclotron by using a network analyzer to obtain the whole eigenfrequency interval of the cavity, wherein the integral eigenfrequency interval is recorded as f 1-f 2;
2) selecting a frequency value f0 which is close to the middle frequency in the cavity eigenfrequency range f 1-f 2, and stopping rotating the capacitor driver;
3) adjusting the cavity coupling capacitance 2 such that S11 is less than-15 dB in the S parameter of the cavity at f 0;
4) setting the frequency of a signal source to be f0 and the power to be 10dBm, carrying out a continuous mode, connecting an output signal of the signal source to a coupling end 1 of a cavity, connecting a cavity capacitance sampling signal (the sampling signal is a capacitance plate, and the coupling end 1 in the figure 1) to an oscilloscope, vacuumizing a rotating capacitance vacuum chamber 6, and keeping the vacuum degree of the rotating capacitance vacuum chamber 6 not higher than 0.1 mbar;
5) selecting a motion mode of the rotating capacitor as a speed mode, and stably increasing the rotating speed of the rotating capacitor to a designed rotating speed, wherein the acceleration of the rotating capacitor is 40-70 rpm/s;
6) and testing the time interval delta x and the reciprocal 1/delta x between the peaks of the sampling cavity capacitance sampling signal by utilizing the scale function of the oscilloscope, wherein 1/delta x is the modulation frequency of the synchrocyclotron (see figure 4).
In step 1), a fixed interval time is set between two adjacent circular motions, and the main reason is that in each motion, a certain length of response time (usually about 1 s) is required for the motion of a rotating capacitor driver, such as a stepping motor, and a network analyzer needs a certain time to prepare for analysis, wherein 4-6s is selected, so that the adjacent two motions of the rotating capacitor cannot be influenced with each other, the motion precision is ensured, and the test efficiency is considered.
In the step 5), in the motion of the rotating capacitor, the acceleration of the rotating capacitor is preferably 50rpm/s, the acceleration is too fast, the stepping motion has an obvious overshoot phenomenon, and the stabilization time of stepping by 1 degree is longer; the acceleration is too slow, not only the motion reaction will be very slow, affecting the efficiency.
Further, in the step 4), the internal resistance of the input signal port of the oscilloscope is set to be 50 ohms.
The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may occur to those skilled in the art without departing from the principle of the invention, and are considered to be within the scope of the invention.
Claims (4)
1. A method for testing modulation frequency of a synchrocyclotron is based on the fact that a periodic rotating capacitor and a rotating capacitor driver are arranged in a cavity of the synchrocyclotron, the rotating capacitor comprises a rotating capacitor rotor (8) blade and a rotating capacitor stator (7) blade, and the method is characterized by comprising the following steps:
1) selecting the motion mode of the rotating capacitor as a position mode, setting circumferential motion with a stepping angle of 0.5-2 degrees, setting time between two adjacent motions, and simultaneously performing S-parameter frequency scanning on the cavity of the synchrocyclotron by using a network analyzer to obtain the whole eigenfrequency interval of the cavity, and recording the frequency interval as f1～f2；
2) Selecting a cavity eigenfrequency interval f1～f2A frequency value f of medium or nearly medium frequency0Stopping rotating the capacitor driver;
3) adjusting the cavity coupling capacitance (2) such that at f0S parameter of chamber11Less than-15 dB;
4) setting the signal source frequency to f0The power is 10dBm, the continuous mode is adopted, the output signal of the continuous mode is connected to a coupling end (1) of the cavity, the cavity capacitance sampling signal is connected to an oscilloscope, the rotating capacitance vacuum chamber (6) is vacuumized, and the vacuum degree of the rotating capacitance vacuum chamber (6) is not higher than 0.1 mbar;
5) selecting a motion mode of the rotating capacitor as a speed mode, and stably increasing the rotating speed of the rotating capacitor to a designed rotating speed;
6) and testing the time interval delta x and the reciprocal 1/delta x between the peaks of the sampling cavity capacitance sampling signal by utilizing the scale function of the oscilloscope, namely the modulation frequency of the synchrocyclotron.
2. The synchrocyclotron modulation frequency test method of claim 1, wherein in the step 1), the interval between two adjacent motions of the rotating capacitor rotor (8) is set to be a fixed value of 3-7 s.
3. The synchrocyclotron modulation frequency test method of claim 1, wherein in the step 4), the internal resistance of the input signal port of the oscilloscope is set to be 50 ohms.
4. The synchrocyclotron modulation frequency test method of claim 1, wherein in the step 5), the acceleration of the rotating capacitor is 40-70 rpm/s.
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