CN115767873A - Continuous variable energy extraction method for synchrotron - Google Patents

Abstract

The invention relates to a method for leading out continuous variable energy of a synchrotron, which comprises the following steps: the particle energy is adjusted by utilizing a high-frequency system of the synchrotron, so that the particle energy passes through a preset energy-changing range, and in the process, the particles stably run in a circular track of the synchrotron by controlling the high-frequency system of the synchrotron and the intensities of dipolar iron, quadrupole iron and hexapole ferromagnetic fields; and continuously exciting the particles overflowing from the transverse phase space stable region into the electrostatic deflector through the radio frequency excitation device in the whole process of the energy of the particle beam passing through the variable energy range, and separating the particles from the circular orbit of the synchrotron under the action of the electrostatic deflector, wherein the energy time interval and the energy value interval of the particles overflowing from the transverse phase space stable region are narrow enough to be considered as meeting the requirement of continuous energy extraction.

Description

Continuous variable energy extraction method for synchrotron

Technical Field

The invention relates to a method for leading out continuous variable energy of a synchrotron.

Background

The synchrotron is a device which makes charged particles move along a fixed circular orbit under the control of magnetic field force in high vacuum and continuously accelerate (raise energy) under the action of the electric field force to reach high energy. In order to maintain the stable particle orbit in the energy increasing process, the synchrotron needs to keep the magnetic field amplitude and the electric field frequency synchronously changed along with the particle energy, and finally the particle beam is led out to provide various particle beams and radiation rays for the fields of basic scientific research, clinical medicine and industrial production. The synchrotron can well regulate the energy of the extracted beam, the energy regulation of a rear end energy reducer is not needed, and the utilization rate of the beam is greatly improved.

With the increasing requirements and research on the application of the extracted particle beam at the terminal, especially in the aspect of three-dimensional point scanning of cancer treatment, the problem of multi-energy slow extraction by conformal irradiation of a shielding body is solved, people solve the problems of secondary particle generation and larger residual radiation, but the problem of long energy switching time still exists, if the characteristic that the synchronous accelerator can actively adjust the energy of the extracted beam can be fully utilized to realize 'extraction and energy change', particles with continuously changed energy can be extracted, so that the characteristic that the synchronous accelerator can actively adjust the energy and the time characteristic of rapid energy adjustment are combined, the average dose rate in the radioactive treatment process of the synchronous accelerator is improved, the application scene of the extracted beam of the synchronous accelerator is further enriched, and a possible solution is provided for the application of ultrahigh dose rate radiotherapy (flash therapy).

In the aspect of multi-energy fast extraction, the applicant of the present application, qinghua university, in the multi-energy extraction method of synchrotron, which is filed by the invention name of "multi-energy extraction method of synchrotron", with the application date of 2022, 3 months and 3 days, the application number of 202210203893.4, proposes a synchrotron multi-energy extraction method, which can provide a plurality of energy platforms for extraction within one cycle of the operation of the synchrotron. At present, similar multi-energy leading-out experiments and reports exist internationally. Experiments for extracting multiple energies were performed for both HIMAC and obtained HIT in japan. The method can lead beams of a plurality of energy platforms in one period, but the time between different energy platforms is long (often in tens of ms or more), mainly because the preparation time before leading is long (mainly, the two reasons are that the strength of a six-stage magnet is longer in lifting time/the high-frequency cavity pressure needs to be adjusted lower to reduce the momentum dispersion of the beams in the leading process, but the high-frequency cavity pressure needs to be increased between the energy platforms to change energy as soon as possible, so that the time consumption is long).

The time consumed by the energy change in one period can be greatly reduced by extracting the particles with continuously changed energy. Currently, the workers in the Malaysia atomic agency and the Japan high Energy Accelerator research center (KEK) have proposed a method for continuous Energy extraction and rapid cycling and published the simulation results of this method (Leo, KWee & Takayama, ken & Adachi, tetsuo & Kawakubo, tadamichi & Dixit, tanuja. (2020). ESCORT: energy sweet compact cycling algorithm. AIP Conference proceedings.95.020015.10.1063/5.0031618.). The method utilizes the phase of adjusting the potential well voltage and the accelerating voltage of the induction accelerator to ensure that particles overflow from a longitudinal phase stable region, the momentum dispersion of the particles is increased after the particles overflow, the separation of the particles in the momentum dispersion direction in a longitudinal phase space is realized, a larger dispersion function is arranged on an extraction section due to the magnetic focusing structure design (lattice design), at the moment, the particles with larger momentum dispersion enter an extraction electrostatic field to be kicked out of a ring due to the transverse-longitudinal coupling effect, and because each ring of the particles is still accelerated, the energy of the particles extracted from each ring is slowly increased, so that the continuous energy extraction is realized, and the continuous depth scanning of the tumor can be realized by matching with the three-dimensional point scanning at the rear end.

The above-mentioned method of continuous energy extraction has the disadvantage that the particles enter the electrostatic deflector to be extracted due to the lateral position change caused by the longitudinal stable region particle overflow and the lateral-longitudinal coupling effect, so that a very thin electrostatic field anode wire is required to be adopted in the process of entering the electrostatic deflector to avoid the particles from colliding with the electrostatic deflector anode wire and being lost.

It is therefore desirable to have a method of continuous energy extraction that avoids the above-mentioned disadvantages.

Disclosure of Invention

In order to solve the technical problem, the invention provides a method for extracting continuous variable energy of a synchrotron, which comprises the following steps: the particle energy is adjusted by utilizing a high-frequency system of the synchrotron, so that the particle energy passes through a preset energy-changing range, and in the process, the particles stably run in a circular track of the synchrotron by controlling the high-frequency system of the synchrotron and the intensity of dipolar iron, quadrupole iron and hexapole ferromagnetic fields; and continuously exciting the particles overflowing from the transverse phase space stable region into the electrostatic deflector through the radio frequency excitation device in the whole process of the energy of the particle beam passing through the variable energy range, and separating the particles from the circular orbit of the synchrotron under the action of the electrostatic deflector, wherein the energy time interval and the energy value interval of the particles overflowing from the transverse phase space stable region are narrow enough to be considered as meeting the requirement of continuous energy extraction.

Unlike the continuous energy extraction fast cycle method proposed by KEK mentioned above, in the synchrotron continuous variable energy extraction method of the present invention, the particles are not extracted in a divided manner in the longitudinal phase space, but are continuously excited by the rf excitation device to overflow from the transverse phase space stable region. According to a common three-order resonance slow extraction method, the horizontal working point of a beam is adjusted to be close to a three-order resonance line through quadrupole iron and the like before extraction, and six-pole iron is used for driving resonance, so that a triangular transverse phase stability region is formed in a phase space, and when the particle emittance exceeds the area of the phase stability region, the particle emittance is extracted along the boundary line of the phase stability region, as shown in fig. 1. By combining the three-order resonance slow extraction method with the beam current energy regulation by utilizing radio frequency waves and square waves, the particles can ensure a stable extraction track based on the change of the relative size relationship between a transverse phase space stable region and emittance, avoid the collision with an anode wire of an electrostatic deflector and improve the extraction efficiency. In addition, the method for continuously variable energy extraction of the synchrotron of the invention also has the advantage of easily controlling beam current shutoff, because the particles can be prevented from overflowing from the transverse phase space stable region by directly closing a radio frequency excitation (RF-KO) device, while the method for continuously extracting energy and rapidly circulating proposed by KEK is inconvenient for rapidly shutting off the extracted beam current because the particles overflowing from the longitudinal phase space are extracted, and therefore, after the particles are prevented from overflowing from the longitudinal phase space, residual particles which have previously overflowed from the longitudinal stable region but not reached the transverse extraction position continue to move in the circular track.

In the synchrotron continuous variable energy extraction method of the present invention, it is preferable that the particles separated from the circular orbit of the synchrotron by the electrostatic deflector are further extracted completely from the circular orbit with the aid of the extraction cutting magnet.

In the process of stable operation of particles in the circular orbit of the synchrotron, the particles are continuously led out, and the energy of the particles is different when the particles overflow from the transverse stable region and enter the electrostatic deflector in different circles. However, although the energy of the extracted particles is separated circle by circle, the energy change amount of a single circle is small (tens of eV level), and the time of the single circle is often lower in the order of μ s and is far smaller than the time interval (tens of ms level) and the energy value interval (MeV level) of the traditional multi-energy extraction, so that the continuous energy extraction can be considered. Obviously, the energy time interval and energy value interval of the particles overflowing from the transverse phase space stability region can be properly controlled, or the particles are not extracted every turn, or the energy of the particles extracted every turn is not the same.

According to a preferred embodiment of the method for continuously extracting variable energy of the synchrotron, the beam energy is adjusted by a synchrotron high-frequency system, so that the beam energy passes through a preset variable energy range in a continuous energy increasing mode or a continuous energy decreasing mode. It should be understood that it is also possible to change the area of the transverse phase space stable region only when the energy of the particle beam cluster is constant, and the effect of the particles continuously overflowing from the boundary of the transverse phase space stable region can be achieved.

According to a preferred embodiment of the method for continuously variable energy extraction of a synchrotron, the synchrotron high-frequency system adjusts the particle beam energy by the provided radio frequency harmonic signal or pulse square wave signal.

Preferably, after the particles are injected into the synchrotron, the particles are accelerated by the synchrotron high-frequency system to a predetermined range of variation energy. In other words, after the particles are injected into the circular orbit of the synchrotron, the pre-acceleration of the particles can be performed as an optional step before the particles reach the predetermined range of variation energy. The pre-acceleration step proposed here can also be omitted if the particle energy of the implanted particles is already within the predetermined range of variation energies.

The method for overflowing the particles from the transverse phase stable region can make the beam transverse emittance larger than the transverse phase space stable region by increasing the beam transverse emittance and/or reducing the area of the transverse phase space stable region. It should be appreciated that reducing the transverse phase steric stabilization zone area includes adjustments to the hexapole iron and/or the quadrupolar iron. Or the distance between the working point and the third-order resonance line is changed by adjusting the quadrupole iron (in direct proportion to the area of the transverse phase space stable region), or the transverse phase space stable region is increased or reduced by adjusting the magnetic field intensity of the hexapole iron (in inverse proportion to the area of the transverse phase space stable region), so that the transverse phase space stable region is reduced relative to the transverse emittance of the beam comprehensively, and partial particles overflow from the transverse direction.

And after the particles scan the whole variable energy range on the energy, closing a radio frequency excitation device (RF-KO), stopping the variable energy process, closing the six-pole iron and other magnet equipment, and finishing the continuous variable energy extraction process.

In addition, according to the working principle of the synchrotron, a plurality of variable energy extraction processes can be repeatedly carried out in one working period or each working period, the variable energy extraction processes are not necessarily all continuous energy rising or continuous energy falling, and a variable energy range of continuous energy rising is connected with a variable energy range of continuous energy falling in the same working period, and continuous variable energy extraction is carried out in both variable energy ranges.

The process can be carried out in a reciprocating mode in each working period of the synchrotron, and a plurality of continuous energy-variable leading-out processes are achieved.

Drawings

Embodiments of the present invention are explained below with reference to the drawings. In the drawings:

fig. 1 schematically shows an example of lateral overflow of particles to the active region of an electrostatic deflector in a synchrotron continuous variable energy extraction method according to the invention;

fig. 2 schematically shows a schematic timing sequence of method steps in a synchrotron continuous variable energy extraction method according to the invention.

Detailed Description

The present invention is explained in detail below with reference to the accompanying drawings.

The individual method steps of the synchrotron continuous variable energy extraction method of the invention are schematically illustrated in fig. 2. After the injection of the particles and, if necessary, the acceleration, the particles reach a predetermined range of energies in the circular orbit. In the variable energy range, the particles are continuously excited by the radio frequency excitation device to overflow from a transverse phase space stable region (as shown in figure 1) into the electrostatic deflector and are separated from a circular orbit of the synchrotron under the action of the electrostatic deflector in the whole process of the energy of the particle beam passing through the variable energy range. The separated particles are completely extracted from the ring track with the further aid of an extraction cutter magnet.

Since the energy of the particles in each circle only differs by tens of electron volts (eV) during the operation of the particles in the circular orbit, the operation time of a single circle is only in the order of mus or even lower, and therefore, the particles extracted in this way can be considered to be continuous energy extraction in corresponding applications.

In the process of slow extraction of the third-order resonance, beam energy is adjusted by utilizing a high-frequency system of a synchrotron, wherein the high-frequency system of the synchrotron can be radio frequency harmonic waves or pulse square signals. In order to reduce the beam momentum dispersion and ensure the extraction efficiency of the third-order resonance method, when the radio frequency harmonic is adopted for energy conversion and adjustment in the extraction process, the radio frequency harmonic cavity voltage needs to be controlled within a reasonable range, for example, the peak voltage is within +/-100V.

In the process of continuous variable energy extraction, the magnetic field strength of magnets such as dipolar iron and quadrupole iron also needs to change along with the energy of synchronous particles to ensure that the closed orbit of the beam current in the cyclotron does not change, as shown in fig. 2.

While embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that: many changes, modifications, substitutions, variations and any combination of these embodiments may be made without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims (10)

1. A method for continuously extracting variable energy of a synchrotron is characterized by comprising the following steps:

adjusting the particle energy by utilizing a high-frequency system of the synchrotron to enable the particle energy to pass through a preset energy-changing range, and enabling the particle beam group to stably run in a circular track of the synchrotron by controlling the high-frequency system of the synchrotron and the intensity of dipolar iron, quadrupole iron and hexapole ferromagnetic fields in the process;

and continuously exciting the particles overflowing from the transverse phase space stable region into the electrostatic deflector by the radio frequency excitation device in the whole process of the energy of the particle beam passing through the variable energy range, and separating the particles from the circular orbit of the synchrotron under the action of the electrostatic deflector, wherein the energy time interval and the energy numerical interval of the particles overflowing from the transverse phase space stable region are narrow enough to be considered as meeting the requirement of continuous energy extraction.

2. The synchrotron continuous variable energy extraction method of claim 1,

the particles separated from the circular orbit of the synchrotron under the action of the electrostatic deflector are completely extracted from the circular orbit by the aid of the extraction cutting magnet.

3. The synchrotron continuous variable energy extraction method according to claim 1 or 2,

and adjusting the energy of the beam cluster by using a high-frequency system of the synchrotron, so that the particle beam cluster passes through a preset energy change range in a continuous energy increasing or reducing mode.

4. The synchrotron continuous variable energy extraction method of claim 3,

the synchrotron high-frequency system adjusts the energy of the particle beam cluster through the provided radio frequency harmonic wave signal or pulse wave signal.

5. The synchrotron continuous variable energy extraction method of claim 4,

after the particles are injected into the synchrotron, the particles are already within a predetermined range of variation energy.

6. The synchrotron continuous variable energy extraction method of claim 4,

after the particles are injected into the synchrotron, the particles are accelerated by the synchrotron high-frequency system to reach a predetermined range of variation in energy.

7. The synchrotron continuous variable energy extraction method according to claim 1 or 2,

and in the energy variation range of the particles, the area of the transverse phase space stable region is changed by adjusting the intensity of the hexapole iron or the quadrupolar iron, so that part of the particles in the particle beam can overflow from the transverse phase space stable region.

8. The synchrotron continuous variable energy extraction method according to claim 1 or 2,

and in the variable energy range of the particle beam, adjusting parameters of a radio frequency excitation device to enable part of particles in the particle beam cluster to overflow from a transverse phase space stable region.

9. The synchrotron continuous variable energy extraction method according to claim 1 or 2,

the synchronous accelerator has a plurality of variable energy ranges in one working period of the synchronous accelerator, and particles in each variable energy range continuously rise in energy or continuously fall in energy, or continuously rise in energy in one part of the variable energy range and continuously fall in energy in the other part of the variable energy range.

10. The synchrotron continuous variable energy extraction method according to claim 1 or 2,

the synchronous accelerator has a plurality of variable energy ranges in a plurality of working cycles of the synchronous accelerator, and the particles in each variable energy range continuously increase in energy or continuously decrease in energy or continuously increase in energy in one part of the variable energy range and continuously decrease in energy in the other part of the variable energy range.

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