CN115515292A

CN115515292A - Proton injector

Info

Publication number: CN115515292A
Application number: CN202211289236.2A
Authority: CN
Inventors: 方文程; 陆羿行; 郭玉森; 赵振堂
Original assignee: Shanghai Advanced Research Institute of CAS
Current assignee: Shanghai Advanced Research Institute of CAS
Priority date: 2022-10-20
Filing date: 2022-10-20
Publication date: 2022-12-23

Abstract

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

Description

Proton injector

Technical Field

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

Background

Proton accelerators are used in a wide variety of medical applications, such as proton therapy, boron Neutron Capture Therapy (BNCT), production of medical isotopes, and the like. However, protons at low energy have the characteristics of low speed and strong space charge effect, and the conventional accelerator has poor beam quality, and needs to use some special acceleration structures. For proton therapy, which requires higher energy, low energy accelerators are used to accelerate and inject the beam into the main accelerator, also referred to as injectors. The energy of the protons is improved after the protons are accelerated by the injector, the speed is greatly improved, the space charge effect is weakened, and the beam quality is easy to control in the subsequent acceleration process, so that the quality of the injector determines the quality of the whole accelerator system to a great extent.

The proton injector mainly comprises an ion source, a low-energy transmission line, a Radio Frequency Quadrupole (RFQ), a drift Tube linear accelerator (DTL), an intermediate energy transmission line and a beam splitter. Wherein, DTL is an accelerator structure composed of a drift tube and an accelerating gap, and DTL is an optimum accelerator type when the proton speed is beta-0.1. The traditional DTL type, namely Alvarez type DTL, has lower acceleration gradient and longer energy length for same acceleration. In addition, the DTL needs to add permanent magnet four-pole iron into the drift tube, so that the process difficulty is high, the possibly generated error is large, and the DTL is difficult to adjust after the processing is finished.

To solve the above problems, the prior art has developed a new DTL type, interdigital drift tube linear accelerator (IH-DTL). This IH-DTL's advantage lies in accelerating the gradient height, can reduce DTL's length greatly, and magnet need not install in the drift tube simultaneously, has reduced the technology degree of difficulty to the scope is wider on the selection of magnet, can choose for use electromagnetic quadrupole iron, can adjust to the error at actual debugging, operation in-process. IH-DTL mainly has two different designs, wherein one of the two designs is APF (Alternating Phase Focusing) beam dynamics design, the IH-DTL of the scheme has low entrance acceptance degree and extremely high requirements on processing errors and operation stability, and once the entrance beam parameters are deviated or the structure has errors, the exit beam parameters can generate great errors and cannot meet the requirements. Another design of IH-DTL is KONUS (Kombinierte small Grad Struktur) beam dynamics design, which can overcome the disadvantages of APF scheme, but its bunching effect in the proton implanter is poor, resulting in poor beam quality.

In addition, since various errors may occur in the machining, assembly, welding, etc., the cavity needs to be tuned to an optimal state. In proton implanters, the prior art typically uses tuning rods for tuning. The tuning rod is inserted into the cavity through a hole on the cavity wall, and the microwave performance of the cavity is changed by controlling the insertion depth of the tuning rod, so that the tuning purpose is realized. The existing scheme is to process a tuning rod with a certain length, calculate the required insertion depth of the tuning rod through a tuning experiment, and then calculate the length of the tuning rod outside a cavity. After several iterations of the experiment, the final parameters were determined and the tuning rod was cut to the required length. The tuning method has low precision and poor repeatability, different human measurement errors can be generated, and errors in the tuning process are difficult to compensate because the tuning rod needs to be cut finally.

Disclosure of Invention

To solve the above problems in the prior art, the present invention provides a proton injector, which adopts a low beam phase and integrated IH-DTL design, and can improve beam quality and achieve more precise tuning.

The invention provides a proton injector which comprises an ion source, a low-energy transmission line, a radio frequency quadrupole accelerator, an interdigital magnetic drift tube linear accelerator, an intermediate energy transmission line and a beam scattering device, wherein the first matching section is arranged between the radio frequency quadrupole accelerator and the interdigital magnetic drift tube; the radio frequency quadrupole accelerator comprises a first cavity, wherein four electrodes are arranged in the first cavity; the interdigital drift tube linear accelerator comprises a second cavity, a third cavity and a second matching section, wherein the second matching section is connected with the second cavity and the third cavity; when the proton beam enters the interdigital drift tube linear accelerator, the proton beam passes through the second bunching section in a first bunching phase, and passes through the third bunching section in a second bunching phase which is smaller than the first bunching phase.

Preferably, the first matching section consists of several electromagnetic quadrupole irons.

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

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

Preferably, the second cavity, the third cavity and the second matching section are designed integrally.

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

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

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

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

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

According to the proton injector provided by the invention, through the double-cavity integrated design of the IH-DTL, the collimation speed and precision of the cavity can be improved, so that the cavity is more stable and the operation is more stable. The optimized IH-DTL parameter design can realize shorter length and smaller energy dispersion of the outlet beam and improve the beam quality. In addition, the invention adopts the design of the tuner which can reciprocate and has higher precision, can accurately control the depth of the tuning rod entering the cavity and realize more accurate tuning of the frequency and field distribution of the cavity.

Drawings

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

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

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

Fig. 4 is a schematic diagram of the structure of the interdigital drift tube linear accelerator in fig. 1.

Fig. 5 is a schematic diagram of the structure of the tuner.

Detailed Description

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

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

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

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

The radio frequency quadrupole accelerator 3 is used for receiving the proton beam transmitted and focused through the low energy transmission line 2 and accelerating the proton beam to the required preset energy. The radio frequency quadrupole accelerator 3 mainly produces stronger focusing effect by four electrodes, solves the emittance growth problem of proton beam under the low energy, adds the modulation on the utmost point head simultaneously, produces acceleration effect. Specifically, the radio frequency quadrupole accelerator 3 comprises a first cavity, the first cavity is provided with four electrodes, and an included angle between two adjacent electrodes is 90 °. The electrode heads are modulated to form a shape similar to a trigonometric function, as shown in fig. 3 (a), the shapes of the two opposite heads are symmetrical, the modulation gradually increases from the inlet to the outlet, and the amplitude of the corresponding curve increases. While the two adjacent pole heads are of opposite shape (the trigonometric function differs by 180 °), as shown in fig. 3 (b), the hatching in the figure indicates the cross-section of the four pole heads, the diagonal lines in the first quadrant indicate the longitudinal section of the pole heads (i.e. both of these two are half pole heads, to represent the pole head curve), and the curve indicates the pole head shape (one pole head is convex and the other is concave at the same position). In the cavity, an electric quadrupole field is formed due to the four pole heads, and a longitudinal electric field is formed due to the trigonometric-like modulation of the pole heads.

In the invention, the type of the radio frequency quadrupole accelerator 3 is a four-wing type, so that better performance can be kept at high frequency, and the pole head is easy to cool. According to the characteristics of RFQ pole head modulation, the radio frequency quadrupole accelerator 3 sequentially comprises a radial matching section, a forming section, a first beam-focusing section and a first accelerating section along the direction of proton beam. In the radial matching section, the focusing force increases from 0 to a maximum value within a short distance, and the proton beam current is losslessly matched with the time-varying focusing force; in the molding section, the synchronous phase is increased from-90 degrees, the longitudinal electric field is increased from 0 degree, and preliminary preparation is made for molding the beam shape and bunching; in the first beamforming section, the synchronization phase is further modulated until a final value; in the first acceleration section, the synchronous phase is not changed any more, and the modulation of the pole head is further increased, so that the acceleration efficiency is improved, and the proton beam is accelerated to the finally required energy.

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

The first matching section 31 is used for connecting the radio frequency quadrupole accelerator 3 and the interdigital drift tube linear accelerator 4, and has the function of converting the transverse shape of a proton beam at the outlet of the radio frequency quadrupole accelerator 3 into the shape required by the interdigital drift tube linear accelerator 4. The first matching section 31 is composed of a plurality of electromagnetic four-pole irons, and the flexible adjustment capability of the first matching section can cope with errors possibly generated by factors in various aspects such as processing, operation and environment, and the proton beam current is ensured to be in a stable and good state.

As shown in fig. 4, the interdigital drift tube linear accelerator 4 includes a second cavity 41 and a third cavity 42, each of which is a structure in which drift tubes 44 are connected to a cavity wall 46 through support rods 45 in a staggered manner, and the cross section of each of the cavities is 180 °, and the center of each of the drift tubes, the center of each of the cavities, and a beam orbit coincide with each other. The second cavity 41 includes a second beam segment for changing the shape of the proton beam and a second acceleration segment for acceleration along the direction of the proton beam, and the third cavity 42 includes a third beam segment and a third acceleration segment along the direction of the proton beam. When the proton beam enters the interdigital drift tube linear accelerator 4, the proton beam passes through the second beam-focusing section with a first beam-focusing phase, and passes through the third beam-focusing section with a second beam-focusing phase smaller than the first beam-focusing phase.

After the proton beam stream is accelerated by the second cavity 41, the motion trends in both the horizontal and vertical directions become defocused, and therefore a second matching section 43 is provided between the second cavity 41 and the third cavity 42 to change the phase space distribution of the proton beam stream. Like the first matching section 31, the second matching section 43 is composed of several electromagnetic quadrupole irons to ensure a better focusing effect. After being focused and adjusted by the second matching section 43, the proton beam current returns to the focus along the movement trend in the horizontal and vertical directions.

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

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

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

The intermediate energy transmission section 5 is used for transmitting and focusing the proton beam accelerated by the interdigital drift tube linear accelerator 4 so as to avoid the over-increased emission intensity of the proton beam in the long-distance drift. In the intermediate energy transmission section 5, the beam energy is relatively high, the emittance growth is relatively slow in the transmission process, and the beam is not accelerated, so that the requirement on errors is low, and real-time adjustment is not needed according to the actual operation condition. Thus, the intermediate energy transmission section 5 of the present invention uses permanent magnet four-pole iron.

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

In order to realize tuning, a tuner 7 is arranged on the first cavity of the radio frequency quadrupole accelerator 3, and the second cavity 41 and the third cavity 42 of the interdigital drift tube linear accelerator 4. As shown in fig. 5, the tuner 7 includes a tuning body 71, a tuning nut 72 provided on the tuning body 71, a screw 73 movably connected to the tuning nut 72, and a tuning rod 74 connected to the screw 73. Wherein the tuning body 71 is fixed on the outer wall of the first, second and/or

third cavities

41, 42, and the tuning rod 74 extends from the bottom of the tuning body 71 and is inserted into the cavity through the opening of the cavity. When the cavity is tuned, the screw rod 73 is adjusted by the tuning nut 72, and the tuning rod 74 is driven by the screw rod 73 to move so as to adjust the depth of the tuning rod 74 inserted into the cavity. The tuner of the invention can accurately control the insertion depth of the tuning rod through a mechanical structure, can realize reciprocating adjustment, and realizes high-precision tuning by utilizing a screw with a small screw pitch. The tuner of the invention can better tune the cavity, reduce the field distribution error to be lower and achieve a better result than the existing tuning mode.

For ease of understanding, the working principle of the proton implanter of the present invention is further explained below by a specific example.

The ion source 1 adopts a compact 2.45GHz ECR ion source with a full permanent magnet structure, and hydrogen is respectively introduced into the ion source 1 through a gas injection port 11 and a microwave input port 13 and microwave power is fed in. The hydrogen forms plasma at the position of the electrode, and protons are separated and extracted by using extraction high pressure, and the extraction energy is 30keV. The low energy transport line 2 transports the protons while focusing them, after which they leave the ion source system in a continuous beam state into the RFQ.

The proton beam first enters the radial matching section of the RFQ where the accelerator aperture is rapidly reduced and the lateral shape of the beam is modulated to enter the acceptance range. In the shaping phase, the modulation of the pole head gradually increases from 0, and the continuous beam current also gradually converges into a beam cluster. In the first beam-focusing segment, the modulation of the pole head is further increased to the maximum value, the beam is further focused into clusters, and the transverse and longitudinal phase space distribution of the clusters oscillate periodically. Finally, the beam enters a first acceleration section, and in the first acceleration section, the maximum modulation of the pole head is basically kept unchanged. The beam current is accelerated to be more than 3.5MeV within the length of 3 meters through RFQ, and the transmission efficiency is more than 80%.

After passing through a first matching section 31 consisting of three electromagnetic four-pole irons, the beam current becomes consistent in phase space distribution, all the movement trends are focused, and the beam current enters IH-DTL. After entering IH-DTL, the beam firstly enters a second beam-condensing section. Since the first matching section 31 focuses the beam and the length of the beam is increased, the second beam-focusing section is required to compress the length of the beam first. The second beam focusing section of the second cavity 42 is 3 accelerating units with synchronous phase of-35 °, and the focused beam enters the second accelerating section, and the length of the beam is longer, so that the synchronous phase of-60 ° is used in the third beam focusing section of the third cavity 43, and the beam is accelerated by the three units and compressed to the desired length. After passing through the third acceleration section of the third cavity 43, the beam energy reaches 7MeV or more.

By now the accelerator part of the whole proton implanter is finished, but then a medium energy transfer line 5 is often needed to transfer the beam from the implanter to the subsequent accelerator. The long-distance drift of the beam current can lead to the continuous increase of the transverse dimension of the beam current, so that the beam current is mainly focused by quadrupole iron in the MEBT, and the beam current is ensured to keep better quality in the long-distance transmission process. After the MEBT is a beam expander 6 for re-de-focusing the beam stream into a continuous beam state while further reducing the beam energy spread. After passing through the beam spreader 6, most of the beams are in the energy range of-0.3 MeV to 0.1MeV, and the beams with the energy spread within +/-50 keV account for more than 80% of the input beams. For example, in the case of an input beam intensity of 18A for the entire implanter, the beam intensity in the ± 50keV range can be spread by more than 14.4A. The invention can meet the injection requirements of most medical accelerators.

The above embodiments are merely preferred embodiments of the present invention, which are not intended to limit the scope of the present invention, and various changes may be made in the above embodiments of the present invention. All simple and equivalent changes and modifications made according to the claims and the content of the specification of the present application fall within the scope of the claims of the present patent application. The invention has not been described in detail in the conventional technical content.

Claims

1. A proton injector is characterized by comprising an ion source, a low-energy transmission line, a radio-frequency quadrupole accelerator, an interdigital magnetic drift tube linear accelerator, an intermediate-energy transmission line and a beam scattering device which are sequentially connected, wherein a first matching section is arranged between the radio-frequency quadrupole accelerator and the interdigital magnetic drift tube; wherein, the first and the second end of the pipe are connected with each other,

the radio frequency quadrupole accelerator comprises a first cavity, and four electrodes are arranged in the first cavity;

the interdigital drift tube linear accelerator comprises a second cavity, a third cavity and a second matching section, wherein the second matching section is connected with the second cavity and the third cavity; when the proton beam enters the interdigital drift tube linear accelerator, the proton beam passes through the second bunching section in a first bunching phase, and passes through the third bunching section in a second bunching phase which is smaller than the first bunching phase.

2. The proton injector of claim 1 wherein said first matching section is comprised of a plurality of electromagnetic quadrupoles.

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

4. The proton injector of claim 1 wherein the first beaming phase is-35 ° and the second beaming phase is-60 °.

5. The proton injector of claim 1 wherein said second cavity, said third cavity, and said second mating section are of a unitary design.

6. The proton injector of claim 1 wherein a tuner is disposed on each of the first, second and third cavities.

7. The proton injector of claim 6, wherein the tuner comprises a tuning body, a tuning nut disposed on the tuning body, a threaded rod movably coupled to the tuning nut, and a tuning rod coupled to the threaded rod.

8. The proton injector of claim 7 wherein the tuning body is secured to an outer wall of the first, second, and/or third chamber body.

9. The proton injector of claim 7 wherein the tuning rods extend from the bottom of the tuning body and are inserted into the first, second, and/or third cavities through openings in the first, second, and/or third cavities.

10. The proton injector of claim 1 wherein the first, second, and third cavities are each fed power through a magnetic-type coupler.