CN117500138B - Beam load dynamic matching method for low-frequency, high-energy and high-current accelerator - Google Patents

Beam load dynamic matching method for low-frequency, high-energy and high-current accelerator Download PDF

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CN117500138B
CN117500138B CN202311358460.7A CN202311358460A CN117500138B CN 117500138 B CN117500138 B CN 117500138B CN 202311358460 A CN202311358460 A CN 202311358460A CN 117500138 B CN117500138 B CN 117500138B
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beam load
impedance
matching
reactance
load
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CN117500138A (en
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雷钰
王志宇
吕银龙
李明
秦伟涛
陈鑫
卢晓通
赵夏青
柴浩男
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Guodian Investment Nuclear Power Tongchuang Beijing Technology Co ltd
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H7/00—Details of devices of the types covered by groups H05H9/00, H05H11/00, H05H13/00
    • H05H7/02—Circuits or systems for supplying or feeding radio-frequency energy
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H13/00—Magnetic resonance accelerators; Cyclotrons
    • H05H13/005—Cyclotrons
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H7/00—Details of devices of the types covered by groups H05H9/00, H05H11/00, H05H13/00
    • H05H7/001—Arrangements for beam delivery or irradiation
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H7/00—Details of devices of the types covered by groups H05H9/00, H05H11/00, H05H13/00
    • H05H7/02—Circuits or systems for supplying or feeding radio-frequency energy
    • H05H2007/025—Radiofrequency systems
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H7/00—Details of devices of the types covered by groups H05H9/00, H05H11/00, H05H13/00
    • H05H7/02—Circuits or systems for supplying or feeding radio-frequency energy
    • H05H2007/027—Microwave systems

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  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Particle Accelerators (AREA)

Abstract

The invention discloses a beam load dynamic matching method for a low-frequency, high-energy and high-current accelerator, which comprises the following steps: determining the value range of the reactance element dynamically matched with the beam load by utilizing complex impedance-admittance analysis through an equivalent circuit model; the adjustment of the corresponding resistance parameters of the beam load is realized through the high-sensitivity resistance element structure; according to the principle of beam load matching, the control logic which is adapted to the principle is utilized to realize the control of the adjustable resistance element, and finally, the dynamic matching of the beam load is realized; the patent breaks through the prior method, and obtains the requirements of beam load dynamic matching adjustment on the resistive element by using an equivalent circuit model and a complex impedance analysis method combined by a digital shape; this patent is through the adjustable resistance element that sets up between coupler and source end, realizes the dynamic adjustment to the coupling degree. The invention gives up the traditional method for presetting the coupling degree, and leads the load impedance formed by the strong current beam load to be always matched with the source end impedance under the dynamic adjustment.

Description

Beam load dynamic matching method for low-frequency, high-energy and high-current accelerator
Technical Field
The invention belongs to the technical field of cyclotrons, and particularly relates to a beam load dynamic matching method for a low-frequency, high-energy and high-current accelerator.
Background
The task of the accelerator radio frequency system is: electromagnetic energy meeting acceleration frequency is transmitted to ions to be accelerated, a radio frequency system of the accelerator consists of a source, a transmission line and a load according to radio frequency and microwave principles, the source is a power source consisting of a signal generator and an amplifier, the transmission line is a bridge for transmitting radio frequency power output to the load under the condition of least loss, the bridge is usually composed of radio frequency coaxial transmission feed pipes (feed lines) or waveguide groups with various structures, and the load is terminal impedance formed by an accelerator cavity and beam current. According to the equivalent circuit principle, the radio frequency system of the accelerator can be described as a circuit schematic diagram as shown below:
Fig. 1 is a schematic diagram of an equivalent circuit of an accelerator rf system: z L is the source impedance, C k is the coupling capacitance (also can be inductance, C, L, R p are the equivalent parallel capacitance, inductance and resistance of the RF accelerating structure, R b is the equivalent resistance of beam current, U L is the load voltage, U f and U r are the incident and reflected voltages, respectively)
In general, the rf transmission line is a standard feed line, feed line or waveguide, and the impedance is fixed, so that when the source and load impedances match, the rf system reaches a resonant state, the output impedance of the source is the output impedance of the final amplifier, and once adjusted, is also a fixed parameter, and only the coupling structure of the transmission line and the rf accelerating structure can be used to adjust the matching state of the whole system. The degree of matching is expressed in terms of the degree of coupling, called the degree of coupling, expressed by the symbol β, according to the microwave principle:
Q 0 and Q e are the quality factors of the load and source, respectively, P 0 and P e are the equivalent power losses (not occurring simultaneously) of the load and source, respectively, and P b and P c are the power losses of the beam and accelerating structure, respectively. According to the microwave principle, U r will be equal to 0 only when β=1. In any other case, U r will be greater than 0, the reflected voltage will return to the source, and in the case of a circulator, the voltage will be absorbed by the circulator load, but for an accelerating structure with a low resonant frequency, the size of the circulator will be abnormally large, and considerable insertion loss is brought, and is generally not used. Thus, for a low resonant frequency rf resonant system, its reflected voltage will return directly to the source side final amplifier. Long-term, high power reflections can damage or even destroy the final amplifier (and for solid state sources the system). This damage increases with increasing degree of mismatch, i.e. degree of coupling deviating from 1, and from the above equation, with increasing beam load. In high flow accelerators, the effect of P b is apparent, and can generally reach the same level as P 0, even greater than P 0.
Conventionally, the value of β is calculated without a beam load (P b =0) and with a beam load (P b is the maximum value), and the average value is taken as a target of β adjustment. Allowing for a more balanced reflection in both cases (a reflection that does not harm the source). However, for high energy, low frequency accelerators, P b＝Eb×Ib>>Pc, conventional pre-tuning β to median is completely inadequate.
Disclosure of Invention
Aiming at the problems existing in the prior art, the invention provides a dynamic matching method for beam load of a low-frequency, high-energy and high-current accelerator, and aims to solve the problem that the method for averaging in the prior art is not suitable for the situation that the beam load of the low-frequency, high-energy and high-current accelerator is greatly changed.
The invention provides the following technical scheme for solving the technical problems:
A dynamic matching method for beam load of a low-frequency, high-energy and high-current accelerator is characterized by comprising the following steps: the method comprises the following steps:
Step one, determining the value range of a reactance element dynamically matched with a beam load by utilizing complex impedance-admittance analysis through an equivalent circuit model, wherein the value range of the reactance element is as follows: a value range of the reactance element when the beam load changes from 0 to a maximum value corresponding to the cyclotron of the current energy and the current intensity;
Step two, adjusting corresponding resistance parameters of the beam load through a high-sensitivity resistance element structure;
Thirdly, according to the principle of beam load matching, the control logic which is adapted to the beam load matching is utilized to control the adjustable resistance element, and finally, the dynamic matching of the beam load is realized; the radio frequency system can be in a matching state under different beam loads, so that the running requirement of the accelerator is met, and the accelerator radio frequency system is not damaged.
Further, the range of the values of the reactance elements dynamically matched with the beam load is determined by the equivalent circuit model through complex impedance-admittance analysis, and the specific process is as follows:
1) Establishing a cyclotron high-frequency system equivalent circuit model comprising beam load;
2) Deducing the cavity input impedance in the equivalent circuit as a function of the beam load according to the equivalent circuit model, and obtaining the relation between the impedance and admittance through the function;
3) According to the relation between the impedance and the admittance, the matching values of the resistance elements under different beam load conditions can be obtained, and the dynamic matching range of the beam load can be summarized.
Further, the step one, step 2), derives the cavity input impedance in the equivalent circuit as a function of the beam load according to the equivalent circuit model, and obtains the relationship between the impedance and admittance through the function;
The specific process is as follows:
(1) According to the circuit principle of a parallel resonant circuit in the third edition of high-frequency electronic circuit (page thirty of the third edition of high-frequency electronic circuit), writing an expression of input impedance according to an equivalent circuit model, wherein the input impedance is equal to the inverse 1/jωC k of a coupling reactance plus the inverse 1/R p of a cavity equivalent resistance and the inverse 1/jωL+jωC of an equivalent reactance;
The impedance expression Z in of the cavity is the second term on the right side of the equal sign of formula (1) (the first term on the left side of the equal sign is used in the derivation from formula (3) to formula (4)), i.e., Z in =r+jx. According to the definition of impedance and admittance, the reciprocal 1/R p of the equivalent resistance of the cavity is represented by conductance G p, the reciprocal 1/jωL+jωC of the reactance of the cavity is represented by susceptance jB, and the admittance form of the cavity input impedance in the equivalent circuit is deduced:
The numerator denominator is multiplied by G p -jB, and the above formula is modified as:
The real and imaginary parts of the above equation are separated to obtain:
expressed by complex impedance
Thus obtaining the impedance-admittance relationship when the cavities are matched, namely:
Further, the matching values of the resistance elements under different beam loads can be obtained by using a complex plane geometry analysis method according to the relation between impedance and admittance in the step 3), and the dynamic matching range of the beam loads can be summarized, which comprises the following steps
(1) The reactance expression when the cavity impedance is matched is deduced according to the relation between the impedance and admittance when the cavity is matched (resonance), b=0, r=1/G p＝Rp, jx=0. The goal of the matching is to match Z in to 50Ω, which means r=50Ω, and therefore, from the conclusion of equation (2) it can be deduced:
(2) According to the complex impedance characteristic (complex impedance_hundred degrees encyclopedia (baidu.com)), -jx=1/jωc k, and the following formula (3), the values of the corresponding matching reactance elements, namely the dynamic matching ranges of the elements, under different beam loads are obtained, and the specific solving relation is as follows:
Further, the second step realizes the adjustment of the corresponding resistance parameter of the beam load through the high-sensitivity resistance element structure, and the specific process is as follows:
1) The stepping motor drives the transmission mechanism to enable a part of pole pieces of the capacitive reactance to rotate, so that the function of adjusting capacitance parameters is realized;
2) The capacitive reactance structure is connected with a coaxial transmission line (a feed pipe or a cable) and then connected with a transmission line system of the accelerator.
Further, the capacitive reactance is formed by a series of metal sheets connected with the inner conductor of the coaxial transmission line and grounded at intervals, the shape of each metal sheet is a part of a circle, the metal sheets are surrounded by a major arc and a bow of the circle, a rotating shaft connected with the coaxial line penetrates through the circle center of the circle where the metal sheets are positioned, the metal sheets contacted with the inner conductor are insulated from the ground, and the metal sheets insulated from the inner conductor are connected with the outer conductor through the short circuit sheets to realize grounding. The rotating shaft is insulated to the ground through insulation treatment.
Further, the specific process of the third step is as follows:
1) Dynamic matching of beam load is enabled;
2) Comparing the incident power and the reflected power of the radio frequency system to obtain a voltage standing wave ratio coefficient;
3) And if the voltage standing wave ratio coefficient is larger than 1.1, the resistance element is adjusted if the voltage standing wave ratio coefficient exceeds the voltage standing wave ratio coefficient, and the adjustment is finished if the voltage standing wave ratio coefficient does not exceed the voltage standing wave ratio coefficient.
Further, the range of values of the reactive element includes a range of values of a coupling capacitance of the coupler.
Further, the range of values of the reactive element includes a range of values of a coupling inductance of the coupler.
Advantageous effects of the invention
1. The design principle of the invention gives up the traditional method for presetting the coupling degree, dynamically adjusts the coupling degree by utilizing the microwave principle, so that the reflection seen by a source end is always minimum, the impedance of the source end is always matched under the dynamic adjustment of the load impedance change formed by the strong current beam load, and finally, the low-frequency, high-energy and strong current accelerator is realized.
2. This patent is different from the main difference of the prior art: the patent breaks through the prior method, and obtains the requirements of beam load dynamic matching adjustment on the resistive element by using an equivalent circuit model and a complex impedance analysis method combined by a digital shape; this patent is through the adjustable resistance component that sets up between coupler and source end (optional position), realizes the dynamic adjustment to the coupling degree.
3. The patent provides a control logic, which utilizes a closed-loop controller to dynamically adjust a resistance element to achieve a state that a load end and a source end are always matched;
Drawings
FIG. 1 is a schematic diagram of a layout of a radio frequency power system of a cyclotron;
FIG. 2 is a schematic diagram showing the structure of dynamic adjustment of beam load according to the present invention;
FIG. 3 is a schematic diagram of a capacitive reactance structure for dynamic matching of beam loads according to the present invention;
FIG. 4 is a block diagram of the dynamic matching control logic of the beam load of the present invention;
Fig. 5 is a flow chart of the method of the present invention.
In the figure: 1: a metal sheet; 2: a rotating shaft; 3: a pole piece connected to the inner conductor; 4: a pole piece connected to the outer conductor; 5: an insulator.
Detailed Description
Principle of design of the invention
1. The innovation point of the invention is as follows: the innovation point is that a method for determining the value range is found. The range of values is a range of values of coupled power reactance elements, which are reactive elements of coupled power for a radio frequency power system of a cyclotron. The meaning of the formula (4) is a method for determining the range, and the value range of the coupling power reactance element can be obtained from the formula no matter how large the beam load change range of the radio frequency power system of the cyclotron is. In this embodiment, the reactance element may be a capacitive reactance, and the capacitive reactance may have a value ranging from C k0 to C kn.
2. Compared with the prior art, the invention has the advantages that: the prior art is provided with a device and a method for reducing high-frequency power reflection of a large-beam current rotary accelerator, and the application number is 2023102783518, and the method is used for establishing a motor compensation amount and strong current relation comparison table in advance. However, it is not known how this table is, typically derived empirically or experimentally, not theoretically, and it is not general and developed for a particular energy, a particular flow intensity of an accelerator. When the energy and flow intensity are changed, the comparison table is not applicable.
The present invention replaces the prior art look-up table with a capacitive reactance structure (fig. 2) in combination with control logic (fig. 4). The method has the advantages of being applicable to all energy accelerators without being limited to a specific accelerator, and having general meaning and universality. This is referred to as "having a general meaning and versatility" because the range of values of the reactive element C k found in accordance with the method of the present invention varies with the accelerator energy. Finding this range (C k0 to C kn) enables to determine the length and diameter of the capacitive reactance structure, since the length and diameter of the capacitive reactance structure is determined by the maximum value of the reactance element C k. The capacitive reactance structure is determined to be the basis, and the load at the right end of the U L in fig. 1 can be adjusted on the basis of the capacitive reactance structure, so that the load Z in at the right end of the U L in fig. 1 is equal to Z L = 50Ω at the left end of the U L, thereby realizing impedance matching of the radio frequency power system of the cyclotron. Without this range it is not known what capacitive reactance structure to make, and if the length is insufficient, the adjustment range is too small to be used, and if the length is too large, the cost is increased, resulting in waste. But capacitive reactance structures only provide a range of adjustment and cannot replace logic control. But without this adjustment range the capacitive reactance structure has uncertainty, and then precise logic control is not useful.
3. The calendar of equation (4):
① Z in and specific element relationships are established. Adjusting C k is equivalent to adjusting the load at two ends of U L in FIG. 1, the right side of U L in FIG. 1 is equal to the power coupling capacitor C k, the accelerator is added with a large equivalent inductance L, a capacitor C and a variable beam load R p, the impedance at the right side of U L is represented by Z in, and a relational expression of Z in and C k、L、C、Rp is established, the relational expression is called a basic relational expression, and the formula (1) is obtained according to the impedance characteristics of high-frequency electronic circuit strings and parallel connection:
② The impedance expression Z in of the cavity is the second term on the right side of the equal sign of formula (1) (the first term on the left side of the equal sign is used in the derivation from formula (3) to formula (4)), i.e., Z in =r+jx. According to the definition of impedance and admittance, the reciprocal 1/R p of the equivalent resistance of the cavity is represented by conductance G p, the reciprocal 1/jωL+jωC of the reactance of the cavity is represented by susceptance jB, and the admittance form of the cavity input impedance in the equivalent circuit is deduced:
The numerator denominator is multiplied by G p -jB, and the above formula is modified as:
The real and imaginary parts of the above equation are separated to obtain:
expressed by complex impedance
Thus obtaining the impedance-admittance relationship when the cavities are matched, namely:
③ The reactance expression when the cavity impedance is matched is deduced according to the relation between the impedance and admittance when the cavity is matched (resonance), b=0, r=1/G p＝Rp, jx=0. The goal of the matching is to match Z in to 50Ω, which means r=50Ω, and therefore, from the conclusion of equation (2) it can be deduced:
④ To make Matching to 50Ω+j0, the circuit needs to be matched through a coupling capacitance jX k, and according to the complex impedance characteristic (complex impedance_hundred degrees encyclopedia (baidu. Com)), -jx=1/jωc k and the formula (3), the value of the corresponding matching reactance element under different beam loads, namely the dynamic matching range of the element, is obtained by taking the formula (4):
according to the principle of the invention, the invention designs a dynamic matching method for beam load of a low-frequency, high-energy and high-current accelerator, which is characterized in that: the method comprises the following steps:
Step one, determining the value range of a reactance element dynamically matched with a beam load by utilizing complex impedance-admittance analysis through an equivalent circuit model, wherein the value range of the reactance element is as follows: a value range of the reactance element when the beam load changes from 0 to a maximum value corresponding to the cyclotron of the current energy and the current intensity;
Step two, adjusting corresponding resistance parameters of the beam load through a high-sensitivity resistance element structure;
Thirdly, according to the principle of beam load matching, the control logic which is adapted to the beam load matching is utilized to control the adjustable resistance element, and finally, the dynamic matching of the beam load is realized; the radio frequency system can be in a matching state under different beam loads, so that the running requirement of the accelerator is met, and the accelerator radio frequency system is not damaged.
Further, the range of the values of the reactance elements dynamically matched with the beam load is determined by the equivalent circuit model through complex impedance-admittance analysis, and the specific process is as follows:
1) Establishing a cyclotron high-frequency system equivalent circuit model comprising beam load;
2) Deducing the cavity input impedance in the equivalent circuit as a function of the beam load according to the equivalent circuit model, and obtaining the relation between the impedance and admittance through the function;
3) According to the relation between the impedance and the admittance, the matching values of the resistance elements under different beam load conditions can be obtained, and the dynamic matching range of the beam load can be summarized.
Further, the step one, step 2), derives the cavity input impedance in the equivalent circuit as a function of the beam load according to the equivalent circuit model, and obtains the relationship between the impedance and admittance through the function;
The specific process is as follows:
(2) According to the circuit principle of a parallel resonant circuit in the third edition of high-frequency electronic circuit (page thirty of the third edition of high-frequency electronic circuit), writing an expression of input impedance according to an equivalent circuit model, wherein the input impedance is equal to the inverse 1/jωC k of a coupling reactance plus the inverse 1/R p of a cavity equivalent resistance and the inverse 1/jωL+jωC of an equivalent reactance;
The impedance expression Z in of the cavity is the second term on the right side of the equal sign of formula (1) (the first term on the left side of the equal sign is used in the derivation from formula (3) to formula (4)), i.e., Z in =r+jx. According to the definition of impedance and admittance, the reciprocal 1/R p of the equivalent resistance of the cavity is represented by conductance G p, the reciprocal 1/jωL+jωC of the reactance of the cavity is represented by susceptance jB, and the admittance form of the cavity input impedance in the equivalent circuit is deduced:
The numerator denominator is multiplied by G p -jB, and the above formula is modified as:
The real and imaginary parts of the above equation are separated to obtain:
expressed by complex impedance
Thus obtaining the impedance-admittance relationship when the cavities are matched, namely:
Further, the matching values of the resistance elements under different beam loads can be obtained by using a complex plane geometry analysis method according to the relation between impedance and admittance in the step 3), and the dynamic matching range of the beam loads can be summarized, which comprises the following steps
(1) The reactance expression when the cavity impedance is matched is deduced according to the relation between the impedance and admittance when the cavity is matched (resonance), b=0, r=1/G p＝Rp, jx=0. The goal of the matching is to match Z in to 50Ω, which means r=50Ω, and therefore, from the conclusion of equation (2) it can be deduced:
(2) According to the complex impedance characteristic (complex impedance_hundred degrees encyclopedia (baidu.com)), -jx=1/jωc k, and the following formula (3), the values of the corresponding matching reactance elements, namely the dynamic matching ranges of the elements, under different beam loads are obtained, and the specific solving relation is as follows:
Further, the second step realizes the adjustment of the corresponding resistance parameter of the beam load through the high-sensitivity resistance element structure, and the specific process is as follows:
1) The stepping motor drives the transmission mechanism to enable a part of pole pieces of the capacitive reactance to rotate, so that the function of adjusting capacitance parameters is realized;
2) The capacitive reactance structure is connected with a coaxial transmission line (a feed pipe or a cable) and then connected with a transmission line system of the accelerator.
Further, the capacitive reactance is formed by a series of metal sheets connected with the inner conductor of the coaxial transmission line and grounded at intervals, the shape of each metal sheet is a part of a circle, the metal sheets are surrounded by a major arc and a bow of the circle, a rotating shaft connected with the coaxial line penetrates through the circle center of the circle where the metal sheets are positioned, the metal sheets contacted with the inner conductor are insulated from the ground, and the metal sheets insulated from the inner conductor are connected with the outer conductor through the short circuit sheets to realize grounding. The rotating shaft is insulated to the ground through insulation treatment.
Further, the specific process of the third step is as follows:
1) Dynamic matching of beam load is enabled;
2) Comparing the incident power and the reflected power of the radio frequency system to obtain a voltage standing wave ratio coefficient;
3) And if the voltage standing wave ratio coefficient is larger than 1.1, the resistance element is adjusted if the voltage standing wave ratio coefficient exceeds the voltage standing wave ratio coefficient, and the adjustment is finished if the voltage standing wave ratio coefficient does not exceed the voltage standing wave ratio coefficient.
Further, the range of values of the reactive element includes a range of values of a coupling capacitance of the coupler.
Further, the range of values of the reactive element includes a range of values of a coupling inductance of the coupler.
Embodiment one:
For a low-frequency, high-energy and high-current cyclotron with proton energy of 120MeV and maximum current intensity of 1mA, the resonant frequency is 44.5MHz, the beam load power range is 0kW to 120kW, the cavity power consumption is about 35kW, the cavity equivalent parallel impedance is 224kΩ, and the transmission line characteristic impedance is 50 Ω.
Rp=224 kΩ when the beam load is 0 kW; from equation (4), ck=1.07 pF; rp=50kΩ when the beam load is 120 kW; according to equation (4), it is obtained that ck=2.24 pF, the basic capacitance of the coupling capacitance of the coupler is adjusted to 1.07pF, and the remaining adjustment of 1.17pF is accomplished by the structure described in the second step of claim 1.
It should be emphasized that the above-described embodiments are merely illustrative of the invention, which is not limited thereto, and that modifications may be made by those skilled in the art, as desired, without creative contribution to the above-described embodiments, while remaining within the scope of the patent laws.

Claims (6)

1. A beam load dynamic matching method for a low-frequency, high-energy and high-current accelerator is characterized by comprising the following steps of: the method comprises the following steps:
Step one, determining the value range of a reactance element dynamically matched with a beam load by utilizing complex impedance-admittance analysis through an equivalent circuit model, wherein the value range of the reactance element is as follows: a value range of the reactance element when the beam load changes from 0 to a maximum value corresponding to the cyclotron of the current energy and the current intensity;
Step two, adjusting corresponding resistance parameters of the beam load through a high-sensitivity resistance element structure;
Thirdly, according to the principle of beam load matching, the control logic which is adapted to the beam load matching is utilized to control the adjustable resistance element, and finally, the dynamic matching of the beam load is realized; the radio frequency system can be in a matching state under different beam loads, so that the running requirement of the accelerator is met, and the accelerator radio frequency system is not damaged;
The range of the values of the reactance elements dynamically matched with the beam load is determined by the equivalent circuit model through complex impedance-admittance analysis, and the specific process is as follows:
1) Establishing a cyclotron high-frequency system equivalent circuit model comprising beam load;
2) Deducing the cavity input impedance in the equivalent circuit as a function of the beam load according to the equivalent circuit model, and obtaining the relation between the impedance and admittance through the function;
3) According to the relation between the impedance and the admittance, the matching values of the resistance elements under different beam load conditions can be obtained, and the dynamic matching range of the beam load can be summarized;
The second step realizes the adjustment of the corresponding resistance parameters of the beam load through the high-sensitivity resistance element structure, and the specific process is as follows:
1) The stepping motor drives the transmission mechanism to enable a part of pole pieces of the capacitive reactance to rotate, so that the function of adjusting capacitance parameters is realized;
2) The capacitive reactance structure is connected with a coaxial transmission line (a feed pipe or a cable) and then connected into a transmission line system of the accelerator;
the third concrete process is as follows:
1) Dynamic matching of beam load is enabled;
2) Comparing the incident power and the reflected power of the radio frequency system to obtain a voltage standing wave ratio coefficient;
3) And if the voltage standing wave ratio coefficient is larger than 1.1, the resistance element is adjusted if the voltage standing wave ratio coefficient exceeds the voltage standing wave ratio coefficient, and the adjustment is finished if the voltage standing wave ratio coefficient does not exceed the voltage standing wave ratio coefficient.
2. The method for dynamically matching beam loads of low-frequency, high-energy and high-current accelerators according to claim 1, wherein the method comprises the following steps of: deducing the cavity input impedance in the equivalent circuit according to the equivalent circuit model in the step 2) as a function of the beam load, and obtaining the relation between the impedance and admittance through the function;
The specific process is as follows:
(1) Writing an expression of input impedance according to an equivalent circuit model, wherein the input impedance is equal to the inverse 1/jωC k of the coupling reactance plus the inverse of the sum of the inverse 1/R p of the equivalent resistance of the cavity and the inverse 1/jωL+jωC of the equivalent reactance;
⑵ The reciprocal 1/R p of the equivalent resistance of the cavity is represented by a conductance G p, the reciprocal 1/jωL+jωC of the reactance of the cavity is represented by a susceptance jB, and the impedance expression Z in of the cavity is the second term on the right side of the equal sign of the formula (1); deriving the cavity input impedance in the equivalent circuit as a function of the flow load, thereby obtaining an impedance-admittance relationship when the cavities are matched, i.e. the quotient of the difference between conductance and susceptance and the sum of the square of conductance and the square of susceptance is equal to the sum of resistance and reactance, i.e.:
3. the method for dynamically matching beam loads of low-frequency, high-energy and high-current accelerators according to claim 1, wherein the method comprises the following steps of: the matching values of the resistance elements under different beam load conditions can be obtained by utilizing a complex plane geometric analysis method according to the relation between impedance and admittance in the step 3), and the dynamic matching range of the beam load can be summarized, wherein the method comprises the following specific steps of
(1) The reactance expression when the cavity impedance is matched is deduced according to the relation between the impedance and admittance when the cavity is matched (Z in = 50Ω), namely:
(2) According to the reactance expression, according to the complex impedance characteristic of the pure capacitive element, carrying-jx=1/jωc k into the expression (3), and obtaining the values of the corresponding matched reactance elements under different beam loads, namely the dynamic matching range of the elements, wherein the specific solving relation is as follows:
4. The method for dynamically matching beam loads of low-frequency, high-energy and high-current accelerators according to claim 1, wherein the method comprises the following steps of: the capacitive reactance is formed by a series of metal sheets which are connected with an inner conductor of a coaxial transmission line and grounded at intervals, the shape of each metal sheet is a part of a circle, the metal sheets are surrounded by a major arc and a bow of the circle, a rotating shaft connected with the coaxial line penetrates through the circle center of the circle where the metal sheets are positioned, the metal sheets contacted with the inner conductor are insulated from the ground, the metal sheets insulated from the inner conductor are connected with the outer conductor through a short circuit sheet to realize grounding, and the rotating shaft is insulated from the ground through insulation treatment.
5. The method for dynamically matching beam loads of low-frequency, high-energy and high-current accelerators according to claim 1, wherein the method comprises the following steps of: the range of values of the reactive element includes a range of values of a coupling capacitance of the coupler.
6. The method for dynamically matching beam loads of low-frequency, high-energy and high-current accelerators according to claim 1, wherein the method comprises the following steps of: the range of values of the reactive element includes a range of values of a coupling inductance of the coupler.
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