Proton helium ion implanter

Abstract

One ECR ion source generates a He < 2 + > ion beam, the other ECR ion source generates a H2 < + > ion beam, the He < 2 + > or H2 < + > ion beam is selected by a deflection magnet and then transmitted and focused by LEBT to enter an RFQ, the focusing factor of the RFQ is increased and then reduced, DTL is IH-DTL designed by adopting KONUS beam dynamics and comprises two KONUS periods, the working frequencies of the RFQ and the DTL are respectively 425MHz, 425MHz, 425MHz, 425MHz, 425MHz, 425MHz, 425MHz, 425MHz, 425MHz, 425MHz, 425MHz, 425MHz, 425MHz, 425MHz, 425MHz, 425MHz, 425MHz, 425MHz, 425MHz, 425MHz, 425MHz, after He < 2 + > or H2 < + > ion beams are accelerated by RFQ and DTL, the MEBT distributes and transmits the ion beams to a downstream accelerator and an isotope production device. According to the proton helium ion implanter provided by the invention, the particle beam can meet the injection requirement of a subsequent synchrotron, the miniaturization of the proton helium ion implanter is realized, and the production of medical isotopes is considered.

Description

Technical Field

[0001] The present invention relates to radio frequency technology, and more particularly to a proton helium ion implanter. Background Art

[0002] Particle beam therapy is an advanced radiotherapy technique that uses charged particles such as protons or heavy ions to treat tumors. This treatment modality has unique physical and biological advantages, enabling high doses of radiation to be delivered precisely to the tumor site while minimizing damage to surrounding healthy tissue.

[0003] In particle beam therapy, the injector plays a vital role. The injector is a low-energy accelerator that accelerates the particle beam to a certain energy and then injects it into the main accelerator for further acceleration. Since particle beams at low energy have the characteristics of slow speed and strong space charge effect, directly using conventional accelerators will result in poor beam quality. Therefore, the injector usually adopts a special acceleration structure to improve the quality of the beam. After the particle beam is accelerated by the injector, its energy is improved, the speed is significantly increased, and the space charge effect is weakened. In this way, in the subsequent acceleration process, the quality of the beam becomes easy to control. Therefore, the performance of the injector largely determines the quality of the entire accelerator system.

[0004] It is known that a medical ion implanter is mainly composed of an ion source system, an RFQ (Radio Frequency Quadruple), and a DTL (Drift Tube Linac).

[0005] The ion source system is responsible for generating and accelerating ions, including the ion source and LEBT (low energy transfer section). The ion source is a device that generates ion beams and provides a particle beam with sufficient current intensity for the accelerator. Its basic principle is to introduce different gases into the cavity, turn the gas into plasma through ionization, and then use the extraction high voltage to accelerate and extract the corresponding ions. The role of LEBT is to distribute, focus and transmit the beam so that the beam can be injected into the RFQ with the required emittance.

[0006] RFQ is an acceleration structure designed for the characteristics of particle beams at low energy. It can achieve longitudinal acceleration and transverse focusing of the beam at the same time. The head modulation characteristics of RFQ usually divide it into four sections: radial matching section, shaping section, bunching section and acceleration section. In the radial matching section, the focusing force increases from 0 to the maximum value within a short distance, and the beam is losslessly matched with the time-varying focusing force. The shaping section begins to modulate the synchronization phase and the longitudinal electric field. The synchronization phase increases from -90° and the longitudinal electric field increases from 0, which preliminarily shapes the beam shape in preparation for bunching. In the bunching section, the synchronization phase and modulation coefficient are further increased until the final value. In the acceleration section, the synchronization phase and modulation coefficient no longer change, reaching the maximum accelerating electric field, and the beam is accelerated to the final energy.

[0007] DTL uses microwave electric fields to accelerate charged particles. It consists of a series of drift tubes and acceleration gaps. Particles move in the drift tubes and are accelerated in the acceleration gaps. The traditional Alvarez-type DTL performs well in accelerating medium- and low-energy charged particles in the energy range of 0.03 to 0.5 MeV. It has the advantages of strong lateral focusing ability, high beam quality, and high acceleration efficiency. However, due to its large size and low acceleration gradient, a longer accelerator length is required to accelerate particles of the same energy. In addition, this type of DTL requires the addition of permanent quadrupole iron in the drift tube, which not only increases the difficulty of the process, but may also introduce large errors, and is difficult to adjust after processing.

[0008] Existing medical ion implanters are used to accelerate protons or carbon ions. The frequency of the RFQ radio frequency field is concentrated in the range of 100MHz-217MHz, which has a low frequency and a large size. Direct application in the acceleration of helium ions has a low cost-effectiveness. Summary of the invention

[0009] In order to solve the problem of accelerating proton helium ions at low energy and avoid the disadvantage of large volume of existing implanter devices, the present invention provides a proton helium ion implanter.

[0010] The proton helium ion implanter according to the present invention comprises an ion source system, an RFQ, a DTL and an MEBT, wherein the ion source system comprises two ECR ion sources and an LEBT, one ECR ion source generates He 2+ ion beam, and another ECR ion source produces H 2 + Ion beam, He 2+ or H 2 + After being selected by the deflection magnet, the ion beam is transmitted and focused by the LEBT into the RFQ. The focusing factor of the RFQ increases first and then decreases. The DTL is an IH-DTL designed with KONUS beam dynamics and includes two KONUS cycles. The operating frequencies of the RFQ and DTL are 425 MHz, He2+ or H 2 + After the ion beam is accelerated by RFQ and DTL, MEBT distributes and transmits the ion beam to downstream accelerators and isotope production devices.

[0011] In a preferred embodiment, the pole of the RFQ is divided into a radial matching section, a pre-bunching section, a main-bunching section, a hybrid-bunching acceleration section and an acceleration section; in the radial matching section, the focusing force increases from 0 to a maximum value; in the pre-bunching section, the synchronization phase slowly changes from -90° to -88°, and the longitudinal electric field increases from 0; in the main-bunching section, the synchronization phase quickly rises to -35°, and the modulation coefficient slowly increases, and the acceleration field is slowly increased while the acceleration efficiency is rapidly improved; in the hybrid-bunching acceleration section, the synchronization phase slowly increases to a final value, and the modulation coefficient increases rapidly; the acceleration section uses a constant synchronization phase, and the modulation coefficient slowly increases while the focusing factor decreases.

[0012] In a preferred embodiment, the RFQ is a four-wing RFQ.

[0013] In a preferred embodiment, a first matching section having a plurality of quadrupole electromagnets is disposed downstream of the RFQ to focus the exit beam of the RFQ to meet the acceptance requirement of the entrance of the DTL.

[0014] In a preferred embodiment, the first matching section further includes a Buncher to further focus the beam and correct the beam energy error.

[0015] In a preferred embodiment, there are more than 20 acceleration units in each KONUS cycle.

[0016] In a preferred embodiment, the IH-DTL has two cavities corresponding to two KONUS cycles to allow independent adjustment of the power, phase and quadrupole electromagnets of each cavity.

[0017] In a preferred embodiment, between the two cavities, the DTL further comprises a second matching section having a plurality of quadrupole electromagnets.

[0018] In a preferred embodiment, the basic structure of IH-DTL includes a transverse focusing section, a 0-phase acceleration section and a bunching section, wherein the transverse focusing section is composed of a number of quadrupole electromagnets to perform transverse focusing of the beam, and the 0-phase acceleration section is designed with more than 17 acceleration units. A bunching section with a lower synchronization phase is added before and after each 0-phase acceleration section to control the phase dispersion of the beam after entering the acceleration section.

[0019] In a preferred embodiment, the length of the IH-DTL is 2.3 meters, and after two KONUS cycles of acceleration, the beam energy reaches above 8MeV / u.

[0020] The proton helium ion implanter according to the present invention is a 425MHz proton helium ion implanter, which is designed to solve the acceleration problem of heavy ion beams at low energy, so that the particle beam can meet the injection requirements of subsequent synchrotron accelerators, realize the miniaturization of the proton helium ion implanter, and take into account the production of medical isotopes, which can better meet the needs of most cancer hospitals. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic structural diagram of a proton helium ion implanter according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0022] The preferred embodiments of the present invention are given below in conjunction with the accompanying drawings and described in detail.

[0023] like Figure 1 As shown, a proton helium ion implanter according to a preferred embodiment of the present invention includes an ion source system, RFQ, DTL and MEBT (Medium Energy Transmission Line), wherein the operating frequencies of RFQ and DTL are 425MHz respectively, and after the ion beam generated by the ion source system is accelerated by RFQ and DTL, MEBT distributes and transmits the beam from the implanter to the downstream accelerator and isotope production device. The operating frequencies of RFQ and DTL of the present invention are higher than those of existing similar facilities, making the RFQ and DTL cavities smaller and allowing a larger electric field to be generated in the cavity, greatly reducing the length and volume of the implanter.

[0024] The ion source system includes two electron cyclotron resonance (ECR) ion sources and LEBT (low energy transfer line). One ECR ion source produces He 2+ ion beam, an ECR ion source produces H 2 + Ion beam, these extracted ions first pass through a deflection magnet to select the ion type, and then pass through the LEBT transmission, the ion beam is focused to a certain extent before leaving the ion source system and entering the RFQ. Specifically, ions of different charge-to-mass ratios are selected to enter the downstream RFQ according to needs due to their different turning radii when passing through the deflection magnet.

[0025] In a preferred embodiment, the ion source is a compact ECR ion source, which has no cathode filament, does not generate impurities, operates stably and reliably, and can realize fast switching of different types of particle beams.

[0026] In the present invention, gas is introduced into the ion source through the gas injection port and the microwave input port and microwave power is fed in. The gas forms plasma at the position of the electrode, and the heavy ions are separated and extracted by the extraction high voltage, which is 20 kV.

[0027] RFQ is an accelerator downstream of the ion source system. The electric quadrupole field excited by four electrodes produces a strong focusing effect, which solves the problem of beam emittance growth at low energy. At the same time, modulation is added to the pole head to produce an acceleration effect.

[0028] In the present invention, RFQ uses a magnetic coaxial coupler to feed RF (radio frequency) power. The working principle of this coupler is based on the interaction of electromagnetic fields. RF power is transmitted from the power source to the coupler through a coaxial cable, and then the electromagnetic field in the cavity is excited by the magnetic coupling ring of the coupler, thereby achieving acceleration of charged particles.

[0029] In the present invention, the pole of the RFQ is divided into a radial matching section, a pre-bunching section, a main-bunching section, a hybrid-bunching acceleration section and an acceleration section. In the radial matching section, the focusing force increases from 0 to a maximum value within a relatively short distance, and the beam is losslessly matched with the focusing force that changes with time. The pre-bunching section begins to modulate the synchronization phase and the longitudinal electric field, the synchronization phase increases from -90°, and the longitudinal electric field increases from 0, thereby initially shaping the beam shape. Different from the shaping section of the traditional RFQ, the length of the pre-bunching section is lengthened, a smaller modulation coefficient (1.02) and more acceleration units (126) are used, and the synchronization phase changes slowly from -90° to -88°, thereby reducing the longitudinal phase oscillation of the beam and better capturing particles. In the main-bunching section, the synchronization phase rises rapidly to -35°, and the modulation coefficient increases slowly, while the acceleration efficiency is rapidly improved and the acceleration field is slowly increased, thereby ensuring the transmission efficiency of the beam and forming a shorter bunch by utilizing the phase change. In the hybrid bunching acceleration section, the synchronization phase increases slowly to the final value, and the modulation coefficient increases rapidly, thereby rapidly increasing the accelerating electric field and completing the bunching. The acceleration section uses a constant synchronization phase, and the modulation coefficient increases slowly while the focusing factor decreases, thereby obtaining a higher acceleration efficiency and accelerating the beam to the designed energy. In particular, the present invention effectively reduces the length of the RFQ by using more acceleration units in the pre-bunching section and increasing the synchronization phase and the modulation coefficient more quickly in the main bunching section.

[0030] The ion beam is in a continuous beam state at the entrance of the RFQ. First, it enters the radial matching section, where the aperture of the accelerator shrinks rapidly, and the lateral shape of the modulated beam allows the RFQ to capture more particles. In the pre-bunching section, the focusing factor reaches the maximum value, the modulation of the pole head slowly increases from 0, maintaining a synchronous phase of -90 degrees, and the continuous beam begins to gather into a bunch. In the main bunching section and the hybrid bunching acceleration section, the modulation of the pole head increases rapidly to the maximum value, and the beam is further gathered into a bunch, and its transverse and longitudinal phase space distributions are both oscillating periodically. Finally, the beam enters the acceleration section, the focusing factor is reduced, ensuring that the modulation coefficient reaches the maximum value, and the pole head maintains the maximum modulation unchanged, which is mainly used to accelerate the beam. The beam passes through the RFQ and is accelerated to more than 1.6MeV / u within a length of 2.5 meters, with a transmission efficiency of more than 90%.

[0031] In the present invention, the focusing factor of the RFQ is first increased and then decreased, which is more in line with the focusing force requirements of the RFQ bunching and acceleration sections, and can achieve higher transmission efficiency while shortening the length. The focusing factor is an important parameter in the RFQ dynamic design, representing the magnitude of the RFQ's focusing force on the beam. The focusing factor of the traditional RFQ remains unchanged in the longitudinal direction, and the RFQ head radius of this design remains unchanged, which is easy to tune. The present invention uses a variable focusing factor to improve the transmission efficiency and acceleration efficiency. Since the radius of the head is variable, the precise control of the electromagnetic field distribution in the RFQ is achieved through the combination of a tuning algorithm and a high-precision tuner. Therefore, the use of a variable focusing factor can effectively reduce beam loss, while allowing the acceleration section to have a higher acceleration gradient, thereby achieving miniaturization and high efficiency of the RFQ.

[0032] In the present invention, the RFQ is a four-wing RFQ, the electrodes are directly connected to the cavity wall, and the positive and negative voltages are realized through the eigenmode of the resonant cavity, so that better performance can be maintained at high frequencies while the size is smaller.

[0033] In the present invention, the RFQ uses a smoother cross-sectional curve, which can effectively reduce the maximum surface electric field and increase the inter-electrode voltage.

[0034] The beam at the RFQ outlet cannot be directly injected into the IH-DTL, so a first matching section is provided downstream of the RFQ to focus the RFQ outlet beam and make it meet the acceptance requirements of the DTL entrance. The first matching section includes three quadrupoles. After passing through the first matching section composed of three quadrupoles, the phase space distribution of the beam becomes consistent, and the movement trend is focused. In the present invention, the quadrupole is an electromagnet, and its flexible adjustment ability can cope with errors that may be caused by various factors such as processing, operation, and environment, and ensure stable and good beam quality. The first matching section also includes a buncher cavity, which further bunches the beam while correcting the beam energy error to ensure the transmission efficiency of the injector.

[0035] DTL is an IH-DTL (Interdigital H-mode DriftingTube Linac), which has a high acceleration gradient and can significantly reduce the length of DTL. At the same time, the magnet does not need to be installed in the drift tube, which reduces the process difficulty and has a wider range of magnet choices. Electromagnetic quadrupole iron can be used, and errors can be adjusted during actual debugging and operation, providing greater flexibility and adjustability.

[0036] In the present invention, the length of the IH-DTL is 2.3 meters.

[0037] In the present invention, IH-DTL adopts KONUS (Kombinierte Null Grad Struktur) beam dynamics design, and the basic structure includes a 0-phase acceleration section, a transverse focusing section and a bunching section, which are used to accelerate and change the beam shape respectively. Among them, the transverse focusing section is composed of three quadrupoles, which focus the beam laterally and improve the transverse shape of the beam, similar to the first matching section. The quadrupole also uses an electromagnet with adjustable magnetic field strength to ensure a better focusing effect. In particular, the 0-phase acceleration section adopts a design of more than 17 acceleration units, and a bunching section with a lower synchronization phase is added before and after each 0-phase acceleration section to control the phase dispersion of the beam after entering the acceleration section. By optimizing the dynamic design, low beam loss in a long acceleration section is achieved, the KONUS cycle is reduced, and the average acceleration gradient is increased to reduce the DTL length.

[0038] In the classic KONUS design, a shorter KONUS cycle (generally no more than 15 acceleration units) is generally used to obtain lower energy dispersion and smaller beam loss, but this will lead to more KONUS cycles, and ultimately make the DTL length longer. In the present invention, each KONUS cycle uses a longer acceleration section, which can reduce the number of KONUS cycles and significantly reduce the DTL length, achieving lower costs while meeting the requirements of medical injectors. In a preferred embodiment, the number of acceleration units in each KONUS cycle exceeds 20, reducing the KONUS cycle to two.

[0039] In the present invention, the IH-DTL cavity is a two-stage design, which allows the power, phase and quadrupole magnet of each cavity segment to be independently adjusted. That is to say, the IH-DTL has two cavities, which are fed with power by coaxial couplers respectively, corresponding to two KONUS cycles. The cross-sectional shape of each cavity is rectangular or circular, and the outer diameter of the cavity along the beam direction is variable, so as to achieve a smoother field distribution and obtain a higher energy gain. Between the two cavities, the DTL also includes a second matching section, including a number of quadrupole irons. In the present invention, the quadrupole irons are electromagnets and can be flexibly adjusted during operation. In the present invention, the two cavities are respectively fed with RF (radio frequency) power by magnetic coaxial couplers, and independent power and phase adjustment can be achieved. This design can make the length of the matching section between the two cavities of the IH-DTL more flexible, without being limited by the requirements of the beam phase.

[0040] Specifically, due to the space charge effect and the influence of the focusing magnet, the length of the beam becomes longer after passing through the matching section, resulting in beam loss after entering the acceleration section, so a focusing section is needed to compress the length of the beam. A lower phase focusing section is designed for each KONUS cycle, which can have a stronger focusing effect and reduce the beam loss in the subsequent acceleration section. (The focusing section is essentially the acceleration unit in the drift tube accelerator. In the KONUS dynamic design, the synchronized particles in the acceleration unit of the focusing section are in a negative phase, and the particles in front of the synchronized particles obtain less energy, and the particles behind the synchronized particles obtain more energy, thereby producing a focusing effect.) After passing through the focusing section, the beam enters the 0-phase acceleration section, which is the most important acceleration part. Due to the use of a longer acceleration section design, the lateral and longitudinal matching of the beam is optimized to ensure transmission efficiency. After a cycle of acceleration, the movement trend of the beam in both the horizontal and vertical directions becomes defocused, and a focusing section is also required to change its lateral phase space distribution. The second matching section between the two cavities is composed of three electromagnetic quadrupoles. After being focused and adjusted by the magnets, the beam moves back to the focusing state in both directions and enters the bunching section of the second KONUS cycle. After two KONUS cycles of acceleration, the beam energy reaches more than 8MeV / u.

[0041] MEBT (Medium Energy Transfer Line) is located downstream of DTL, and its main function is to transmit and distribute beams to ensure that the beam maintains good quality during transmission over longer distances. In order to prevent the beam from drifting too large in the lateral direction during long distances, a quadrupole iron is needed to focus the beam. At the same time, in order to distribute the beam to isotope production and synchrotron injection, a dipole iron is needed to deflect the beam. In this part, MEBT transmits different types of ion beams and needs to be adjusted according to the operating conditions. Based on the above reasons, the MEBT in the present invention uses a flexible and adjustable electromagnet.

[0042] The debuncher is the last part of the entire injector. Its main function is to further reduce the energy dispersion of the beam, increase the proportion of the beam injected into the synchrotron, and ensure that more beam can enter the subsequent accelerator.

[0043] In the present invention, MEBT also includes a stripper for H 2 + The extranuclear electrons of the ions are stripped to change the charge-to-mass ratio of the particles to improve the acceleration efficiency of the particle beam in the subsequent main accelerator. In a preferred embodiment, the stripper is a carbon plate. For example, when the input beam intensity of the entire injector is 5000eμA, the beam intensity within the range of ±7keV after acceleration is greater than 4500eμA (90%).

[0044] In summary, the implanter of the present invention is a proton helium ion implanter with a miniaturized design. By increasing the operating frequency and optimizing the beam dynamics, the miniaturization and high transmission efficiency (greater than 90%) of the particle implanter with a charge-to-mass ratio greater than 1 / 2 are achieved. 2 + and 4 He 2+ Accelerated to 8MeV / u, so that the particle beam can meet the injection requirements of subsequent synchrotrons. In particular, the long-distance drift of the beam will cause its lateral size to continue to increase, so in MEBT, the beam is mainly focused by quadrupole iron. Since MEBT transmits a variety of heavy ion beams, the beam parameters will change, so more flexible electromagnets are used. Use dipole iron to deflect the beam to complete the beam distribution. The beam must be stripped before entering the main accelerator to increase the charge-to-mass ratio of the particles, which is beneficial to improving the acceleration efficiency of the main accelerator. After MEBT, the beam current intensity within the energy dispersion range of ±7keV is more than 90% of the input beam. With a beam energy of 8MeV, a larger reaction cross section can be obtained during nuclear reactions for isotope production, thereby improving the efficiency of medical isotope production.

[0045] The above is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. The above embodiment of the present invention can also be modified in various ways. That is, all simple, equivalent changes and modifications made according to the claims and the description of the present invention fall within the scope of protection of the claims of the present invention. The contents not described in detail in the present invention are all conventional technical contents.

Claims

1. A proton helium ion implanter, characterized in that: The proton helium ion implanter includes an ion source system, RFQ, DTL and MEBT, wherein the ion source system includes two ECR ion sources and LEBT, one ECR ion source generates He 2+ Ion beam, another ECR ion source produces H2 + Ion beam, He 2+ or H2 + After being selected by the deflection magnet, the ion beam is transmitted and focused by the LEBT into the RFQ. The focusing factor of the RFQ increases first and then decreases. The DTL is an IH-DTL designed with KONUS beam dynamics and includes two KONUS cycles. The operating frequencies of the RFQ and DTL are 425 MHz, He 2+ or H2 + After the ion beam is accelerated by RFQ and DTL, MEBT distributes and transmits the ion beam to downstream accelerators and isotope production devices.

2. The proton helium ion implanter according to claim 1, characterized in that: The pole of RFQ is divided into radial matching section, pre-bunching section, main-bunching section, hybrid-bunching acceleration section and acceleration section; in the radial matching section, the focusing force increases from 0 to the maximum value; in the pre-bunching section, the synchronization phase slowly changes from -90° to -88°, and the longitudinal electric field increases from 0; in the main-bunching section, the synchronization phase quickly rises to -35°, and the modulation coefficient slowly increases, which slowly increases the acceleration field while rapidly improving the acceleration efficiency; in the hybrid-bunching acceleration section, the synchronization phase slowly increases to the final value, and the modulation coefficient increases rapidly; the acceleration section uses a constant synchronization phase, and the modulation coefficient slowly increases while the focusing factor decreases.

3. The proton helium ion implanter according to claim 1, characterized in that: The RFQ is a four-wing type RFQ.

4. The proton helium ion implanter according to claim 1, characterized in that: A first matching section with several quadrupole electromagnets is arranged downstream of the RFQ to focus the exit beam of the RFQ to meet the acceptance requirement of the entrance of the DTL.

5. The proton helium ion implanter according to claim 4, characterized in that: The first matching section also includes a Buncher to further focus the beam and correct the beam energy error.

6. The proton helium ion implanter according to claim 1, characterized in that: There are more than 20 acceleration units in each KONUS cycle.

7. The proton helium ion implanter according to claim 1, characterized in that: The IH-DTL has two cavities corresponding to two KONUS cycles to allow independent adjustment of the power, phase and quadrupole electromagnet of each cavity.

8. The proton helium ion implanter according to claim 7, characterized in that: Between the two cavities, the DTL further comprises a second matching section having a number of quadrupole electromagnets.

9. The proton helium ion implanter according to claim 1, characterized in that: The basic structure of IH-DTL includes a transverse focusing section, a 0-phase acceleration section and a bunching section. The transverse focusing section is composed of several quadrupole electromagnets to focus the beam laterally. The 0-phase acceleration section adopts a design of more than 17 acceleration units. A bunching section with a lower synchronization phase is added before and after each 0-phase acceleration section to control the phase dispersion of the beam after entering the acceleration section.

10. The proton helium ion implanter according to claim 1, characterized in that: The length of IH-DTL is 2.3 meters. After two KONUS cycles of acceleration, the beam energy reaches above 8MeV / u.

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