Synchrotron Continuously Variable Energy Extraction Method

Abstract

The present invention relates to a synchrotron continuous variable energy extraction method, comprising the following steps: using a synchrotron high-frequency system to adjust particle energy so that the particle energy passes through a predetermined variable energy range; during this process, by controlling the synchrotron high-frequency system and the strength of the dipole iron, quadrupole iron, and hexapole iron magnetic fields, the particles are allowed to stably run in a circular orbit of the synchrotron; during the entire process of the particle beam energy passing through the variable energy range, a radio frequency excitation device is used to continuously excite the particles to overflow from a transverse phase space stable region and enter an electrostatic deflector, and the particles are separated from the circular orbit of the synchrotron under the action of the electrostatic deflector, wherein the energy time interval and energy value interval of the particles overflowing from the transverse phase space stable region are sufficiently narrow so as to be considered to meet the requirements of continuous energy extraction.

Description

Technical Field

[0001] The invention relates to a synchrotron continuous variable energy extraction method. Background Art

[0002] A synchrotron is a device that forces charged particles to move along a fixed circular orbit in a high vacuum, controlled by a magnetic field. Electric fields continuously accelerate (increase energy) them to high energies. To maintain the stability of the particle orbits during the energy-raising process, the synchrotron must synchronize the magnetic field amplitude and electric field frequency with the particle energy. This ultimately generates a particle beam, providing a variety of particle beams and radiation for basic scientific research, clinical medicine, and industrial production. Synchrotrons can finely regulate the extracted beam energy, eliminating the need for a back-end de-escalator, significantly improving beam utilization.

[0003] With the increasing demand and research on terminal applications of extracted particle beams, especially in three-dimensional point scanning for cancer treatment, people have solved the problems of secondary particle generation and large residual radiation, from using shields for conformal irradiation to multi-energy slow extraction. However, the problem of long energy switching time still exists. If we can fully utilize the synchrotron accelerator's ability to actively adjust the extracted beam energy and achieve "emission while changing energy", particles with continuously changing energy can be extracted, thereby combining the synchrotron accelerator's ability to actively adjust energy with the time characteristics of rapid energy adjustment, improving the average dose rate during synchrotron radiotherapy, further enriching the application scenarios of synchrotron extracted beams, and providing a possible solution for the application of ultra-high dose rate radiotherapy (flash therapy).

[0004] In terms of fast multi-energy extraction, the applicant of this application, Tsinghua University, proposed a multi-energy extraction method for a synchrotron in its application date of March 3, 2022, application number 202210203893.4, and invention name “Multi-energy extraction method for a synchrotron”. This method can provide multiple energy platforms for extraction within one cycle of synchrotron operation. Currently, there are similar multi-energy extraction experiments and reports internationally. Both HIMAC and HIT in Japan have conducted multi-energy extraction experiments. This method can extract beams from multiple energy platforms within one cycle, but the time between different energy platforms is long (often on the scale of tens of milliseconds or even more), mainly due to the long preparation time before extraction (mainly due to the following two reasons: the time to increase the strength of the six-stage magnet is long / the high-frequency cavity pressure needs to be lowered to reduce the dispersion of the beam momentum during the extraction process, but the high-frequency cavity pressure needs to be increased between the multiple energy platforms to change the energy as quickly as possible, resulting in a long time consumption).

[0005] Inducing particles with continuously varying energies can significantly reduce the time required to change energy within a cycle. Currently, researchers from the Malaysian Atomic Energy Agency and the High Energy Accelerator Research Center (KEK) in Japan have proposed a method for continuous energy extraction and rapid cycling, and published simulation results of this method (Leo, Kwee & Takayama, Ken & Adachi, Tetsuo & Kawakubo, Tadamichi & Dixit, Tanuja. (2020). ESCORT: Energy sweep compact rapid cycling hadron therapy. AIP Conference Proceedings. 2295.020015.10.1063 / 5.0031618.). This method uses the phase adjustment of the potential well voltage and acceleration voltage of the induction accelerator to make particles overflow from the longitudinal phase stability region. After the overflow, the momentum dispersion of the particles increases, realizing the separation of the momentum dispersion direction of the particles in the longitudinal phase space. In the extraction section, due to the larger dispersion function in the magnetic focusing structure design (lattice design), due to the horizontal and vertical coupling effect, the particles with larger momentum dispersion enter the extraction electrostatic field and are kicked out of the loop. Since the particles are still accelerating in each circle, the energy of the particles extracted in each circle is slowly increasing, thereby realizing continuous energy extraction. Combined with the back-end three-dimensional point scanning, continuous depth scanning of the tumor can be achieved.

[0006] The disadvantage of the above-mentioned continuous energy extraction method is that due to the lateral position change caused by the overflow of particles in the longitudinal stable zone and the transverse and longitudinal coupling, the particles enter the electrostatic deflector for extraction. Therefore, a very thin electrostatic field anode wire is required in the process of the particles entering the electrostatic deflector to avoid the particles colliding with the electrostatic deflector anode wire and being lost.

[0007] Therefore, it is desirable to have a method for continuous energy extraction that can avoid the above disadvantages. Summary of the Invention

[0008] To solve the above technical problems, the present invention provides a method for continuously variable energy extraction from a synchrotron. The method comprises the following steps: using a synchrotron high-frequency system to adjust particle energy so that the particle energy passes through a predetermined variable energy range. During this process, the particles are allowed to stably operate in a circular orbit of the synchrotron by controlling the synchrotron high-frequency system and the magnetic field strengths of the dipole iron, quadrupole iron, and hexapole iron. During the entire process of the particle beam energy passing through the variable energy range, a radio frequency excitation device is used to continuously excite the particles to overflow from a stable region of transverse phase space and enter an electrostatic deflector. The particles are then separated from the circular orbit of the synchrotron under the action of the electrostatic deflector. The energy time interval and energy value interval of the particles overflowing from the stable region of transverse phase space are sufficiently narrow to be considered to meet the requirements of continuous energy extraction.

[0009] Different from the above-mentioned method of continuous energy extraction fast cycle proposed by KEK, in the synchrotron continuous variable energy extraction method of the present invention, particles are not extracted in a segmented manner in the longitudinal phase space, but are continuously excited by the radio frequency excitation device to overflow from the stable region of the transverse phase space. According to the commonly used third-order resonance slow extraction method, before extraction, the horizontal working point of the beam is adjusted to be close to the third-order resonance line by means of quadrupole iron, etc., and the resonance is driven by hexapole iron, thereby forming a triangular transverse phase stable region in the phase space. When the particle emittance exceeds the area of ​​the phase stable region, it will be extracted along the dividing line of the phase stable region, such as Figure 1 As shown. By combining the above-mentioned third-order resonant slow extraction method with the beam energy modulation using radio frequency waves and square waves, particles can ensure a relatively stable extraction orbit based on the change in the relative size relationship between the transverse phase space stable region and the emittance, avoiding collision with the electrostatic deflector anode wire and improving the extraction efficiency. In addition, the synchrotron continuous variable energy extraction method of the present invention also has the advantage of easy control of beam shutdown, because particles can be prevented from overflowing from the transverse phase space stable region by directly shutting down the radio frequency excitation (RF-KO) device. The continuous energy extraction fast cycle method proposed by KEK extracts particles that overflow from the longitudinal phase space. Therefore, after preventing the particles from overflowing from the longitudinal phase space, there will be residual particles that have previously overflowed from the longitudinal stable region but have not reached the transverse extraction position and continue to move in the circular orbit, making it inconvenient to quickly shut down the extraction beam.

[0010] In the synchrotron continuous energy variable extraction method of the present invention, preferably, the particles separated from the circular track of the synchrotron under the action of the electrostatic deflector are further completely extracted from the circular track with the assistance of an extraction cutting magnet.

[0011] During the stable orbit of a synchrotron, particles are continuously extracted, and the energy of the particles as they escape from the transverse stability zone and enter the electrostatic deflector varies from turn to turn. However, while the energy of the extracted particles varies from turn to turn, the energy change per turn is very small (on the order of tens of eV), and the turn time is often in the microsecond range or even lower, far shorter than the energy time intervals (on the order of tens of milliseconds) and energy value intervals (on the order of MeV) of traditional multi-energy extraction. Therefore, it can be considered continuous energy extraction. Clearly, the energy time intervals and energy value intervals of particles escaping from the transverse phase space stability zone can be appropriately controlled, either eliminating the extraction of particles in every turn or eliminating the need for the extraction of particles of the same energy in every turn.

[0012] According to a preferred embodiment of the synchrotron continuously variable energy extraction method of the present invention, the synchrotron high-frequency system is used to adjust the particle bunch energy, allowing the particle bunch to continuously increase or decrease its energy through a predetermined variable energy range. It should be understood that it is also feasible to change only the area of ​​the transverse phase space stable region while keeping the particle bunch energy constant, thus achieving the same effect of continuously overflowing the boundary of the transverse phase space stable region.

[0013] According to a preferred embodiment of the synchrotron continuous variable energy extraction method of the present invention, the synchrotron high-frequency system adjusts the particle beam energy by providing a radio frequency harmonic signal or a pulsed square wave signal.

[0014] Preferably, after the particles are injected into the synchrotron, they are accelerated by the synchrotron's high-frequency system to a predetermined variable energy range. In other words, after the particles are injected into the synchrotron's circular orbit, pre-acceleration of the particles can be performed as an optional step before the particles reach the predetermined variable energy range. If the particle energy of the injected particles is already within the predetermined variable energy range, the pre-acceleration step described herein can be omitted.

[0015] The method for causing particles to overflow from the transverse phase stable region can be to increase the transverse emittance of the beam and / or reduce the area of ​​the transverse phase space stable region so that the transverse emittance of the beam is greater than the transverse phase space stable region. It should be understood that reducing the area of ​​the transverse phase space stable region includes adjusting the hexapole iron and / or quadrupole iron. Or by adjusting the quadrupole iron to change the distance between the working point and the third-order resonance line (proportional to the area of ​​the transverse phase space stable region), or by adjusting the magnetic field strength of the hexapole iron (inversely proportional to the area of ​​the transverse phase space stable region) to increase or reduce the transverse phase space stable region, so that the transverse phase space stable region is reduced relative to the transverse emittance of the beam, so that some particles overflow from the transverse direction.

[0016] After the particles have scanned the entire energy range, the radio frequency excitation device (RF-KO) can be turned off, the energy conversion process can be stopped, and the hexapole iron and other magnetic equipment can be turned off to complete the continuous energy conversion extraction process.

[0017] In addition, according to the working principle of the synchrotron accelerator, multiple energy variable extraction processes can be repeatedly performed within one working cycle or within each working cycle. These energy variable extraction processes are not necessarily all continuous energy increase or all continuous energy decrease. In the same working cycle, a variable energy range of continuous energy increase can be connected to an energy variable range of continuous energy decrease, and continuous energy variable extraction can be performed in both energy variable ranges.

[0018] The above process can be repeated in each working cycle of the synchrotron to achieve multiple continuous variable energy extraction processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The embodiments of the present invention are explained below with reference to the accompanying drawings. In the accompanying drawings:

[0020] Figure 1 Schematically shows an example of particles laterally overflowing into the action area of ​​the electrostatic deflector in the synchrotron continuous variable energy extraction method according to the present invention;

[0021] Figure 2 The figure schematically shows the schematic timing sequence of each method step in the synchrotron continuous variable energy extraction method according to the present invention. DETAILED DESCRIPTION

[0022] The present invention is explained in detail below with reference to the accompanying drawings.

[0023] Figure 2 The various steps of the synchrotron continuous variable energy extraction method of the present invention are schematically shown in FIG. After the particle injection and the acceleration performed when necessary, the particles reach a predetermined variable energy range within the circular orbit. In this variable energy range, during the entire process of the particle beam energy passing through the variable energy range, the radio frequency excitation device continuously excites the particles to overflow from the transverse phase space stable region (such as Figure 1 The particles are then deflected into an electrostatic deflector and separated from the circular orbit of the synchrotron accelerator under the action of the electrostatic deflector. The separated particles are completely extracted from the circular orbit with the further assistance of an extraction cutting magnet.

[0024] Since the particle energy of each circle in the circular orbit differs by only tens of electron volts (eV), and the time for a single circle is only in the μs level or even lower, the particles extracted in this way can be regarded as continuous energy extraction in corresponding applications.

[0025] During the slow extraction process of third-order resonance, the beam energy is adjusted using the synchrotron high-frequency system, which can be a radio frequency harmonic or pulsed square wave signal. To reduce beam momentum dispersion and ensure the efficiency of the third-order resonance extraction method, the radio frequency harmonic cavity voltage must be controlled within a reasonable range, for example, within a peak voltage of ±100V, when variable energy adjustment is used during the extraction process.

[0026] In the process of continuous energy extraction, the magnetic field strength of the dipole iron, quadrupole iron and other magnets also needs to change with the energy of the synchronized particles to ensure that the closed orbit of the beam in the synchrotron motion remains unchanged, such as Figure 2 shown.

[0027] Although the embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, variations and any combinations thereof may be made without departing from the principles and purpose of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A synchrotron continuous variable energy extraction method, characterized in that: The synchrotron continuous variable energy extraction method comprises the following steps: The particle energy is adjusted using the synchrotron high-frequency system so that the particle energy passes through a predetermined energy range. During this process, the particle bunch is kept stable in the synchrotron's circular orbit by controlling the synchrotron high-frequency system and the strength of the dipole, quadrupole, and hexapole magnetic fields. During the entire process of the particle beam energy passing through the energy variable range, the particles are continuously excited by the radio frequency excitation device to overflow from the transverse phase space stable region and enter the electrostatic deflector, and are separated from the circular orbit of the synchrotron accelerator under the action of the electrostatic deflector, wherein the energy time interval and energy value interval of the particles overflowing from the transverse phase space stable region are sufficiently narrow to be considered to meet the requirements of continuous energy extraction. The high-frequency system of the synchrotron is used to adjust the energy of the particle bunch, so that the particle bunch passes through the predetermined energy range in a continuous energy increase or decrease manner. The synchrotron high-frequency system adjusts the particle bunch energy by providing a radio frequency harmonic signal or a pulse wave signal.

2. The synchrotron continuous variable energy extraction method according to claim 1, characterized in that: The particles separated from the circular track of the synchrotron under the action of the electrostatic deflector are completely extracted from the circular track with the assistance of the extraction cutting magnet.

3. The synchrotron continuous variable energy extraction method according to claim 1 or 2, characterized in that: After the particles are injected into the synchrotron, they are already in a predetermined energy range.

4. The synchrotron continuous variable energy extraction method according to claim 1 or 2, characterized in that: After the particles are injected into the synchrotron, they are accelerated by the synchrotron high-frequency system to a predetermined energy range.

5. The synchrotron continuous variable energy extraction method according to claim 1 or 2, characterized in that: Within the variable energy range of the particles, the area of ​​the transverse phase space stable region is changed by adjusting the strength of the hexapole iron or quadrupole iron, so that some particles in the particle beam can overflow from the transverse phase space stable region.

6. The synchrotron continuous variable energy extraction method according to claim 1 or 2, characterized in that: Within the variable energy range of the particle beam, some particles in the particle bunch can overflow from the transverse phase space stable region by adjusting the parameters of the radio frequency excitation device.

7. The synchrotron continuous variable energy extraction method according to claim 1 or 2, characterized in that: There are multiple energy ranges in one working cycle of the synchrotron accelerator. In each energy range, particles continuously increase or decrease energy, or continuously increase energy in a part of the energy range and continuously decrease energy in another part of the energy range.

8. The synchrotron continuous variable energy extraction method according to claim 1 or 2, characterized in that: There are multiple energy ranges within multiple working cycles of the synchrotron accelerator. In each energy range, particles continuously increase or decrease energy, or continuously increase energy in a part of the energy range and continuously decrease energy in another part of the energy range.

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