A compact proton injector

Abstract

The application provides a compact proton injector, comprising an ion source system, an RFQ and an IH-DTL connected in sequence, the working frequency of the RFQ and the IH-DTL is 714MHz, so that the total length of the RFQ and the IH-DTL is less than 3 meters, and the beam output energy of the IH-DTL is higher than 8MeV. The working frequency of the compact proton injector is set to 714MHz, so that the acceleration gradient of the IH-DTL can be increased to 9MV / m, and the acceleration gradient of the RFQ reaches 2MV / m, so that the total length of the RFQ and the IH-DTL is less than 3 meters, thereby reducing the volume and weight of the injector and reducing the construction cost.

Description

Technical Field

[0001] This invention belongs to the field of charged particle accelerators, specifically relating to a proton injector used to provide a high-quality beam for a proton linear accelerator, and can also be used as an injector for other types of proton accelerators. Background Technology

[0002] Proton accelerators are a key component of proton therapy devices, providing a suitable proton beam. There are three common types of accelerators: cyclotrons, synchrotrons, and linear accelerators. Each type has its advantages and disadvantages: cyclotrons have a fixed output energy, which can only be reduced by an absorber to meet different energy requirements in proton therapy; their output flux is also relatively low. Synchrotrons have actively adjustable output energy, achieved by changing parameters of some components; their modulation response time is relatively long, on the order of seconds, and their output flux is also not high. Linear accelerators not only have actively adjustable output energy, but also achieve modulation by controlling microwave power; their modulation response time is extremely short, on the order of milliseconds, and they can achieve very high output flux. Therefore, linear accelerators have advantages in proton therapy, and almost only linear accelerators can meet the needs of the emerging flash therapy (high-dose-rate radiotherapy, FLASH). Currently, there are relatively mature solutions and products for cyclotrons and synchrotrons, but there is still no reliable solution for linear accelerators. One of the important reasons for this is the lack of a suitable low-energy accelerator—that is, injector—solution.

[0003] The proton injector is crucial in the entire accelerator, and its performance largely determines the overall performance of the accelerator. At low energies, protons are characterized by slow velocity and strong space charge effects. Acceleration by conventional accelerators results in poor beam quality. However, after acceleration by an injector, the proton energy is increased, the velocity is greatly enhanced, and the space charge effect is weakened, making beam quality easier to control in subsequent acceleration processes. Therefore, parameters such as the injector's transmission efficiency, output beam intensity, and output beam emittance greatly determine the parameters of the entire accelerator.

[0004] Existing injector designs are difficult to apply to linear accelerators. They generally have the following characteristics: low operating frequencies, ranging from tens of megahertz in the early days to the commonly used 300-400 megahertz today; large size and weight; and high construction costs. The main reason for this is that, in order to inject a beam into a subsequent linear accelerator, the injector's frequency must be an integer fraction of the main accelerator's frequency. However, due to the development of accelerator technology and the influence of power sources, linear accelerators mainly operate in the S-band (2856, 2998 MHz). Therefore, existing injector designs cannot meet the injection requirements of linear accelerators.

[0005] Existing proton injectors mainly consist of an ion source, a low-energy transmission line, a radio frequency quadruple accelerator (RFQ), and a drifting tube linear accelerator (DTL). In existing devices, the DTL section is primarily of the Alvarez type. Current accelerator frequencies are mainly 216MHz, 325MHz, and 425MHz, which are not integer fractions of the main accelerator's frequency. These frequencies are clearly insufficient to meet the injection requirements of the linear accelerator.

[0006] The ion source is the origin of the entire system and the place where protons are produced. The basic principle of the ion source is to introduce hydrogen gas into the cavity, ionize the hydrogen gas into plasma, and then use the extraction high voltage to increase the velocity of the corresponding particles and extract them. The low-energy transport section (LEBT) is usually considered as part of the entire ion source system. Its function is to transport the beam and adjust its parameters to meet the injection requirements of RFQ.

[0007] The RFQ (Radio Frequency Quadrature) is an acceleration structure invented to address the characteristics of proton beams at low energies. It primarily utilizes four electrodes to generate a strong focusing effect, solving the problem of proton beam emission increase at low energies. Modulation is added to the electrode tips to produce an acceleration effect. There are two main types of RFQs: four-bar and four-wing. The main difference lies in the shape of the electrodes. In a four-bar RFQ, the electrodes are rod-shaped and alternately connected to a support plate via metal plates to create positive and negative voltages. In a four-wing RFQ, the electrodes are directly connected to the cavity wall, achieving positive and negative voltages through a circumferential phase difference. The four-wing RFQ has a cavity with four electrodes. In cross-section, the four electrodes are distributed at 90°. The electrode tips are modulated to form a trigonometric function-like shape, with the shapes of relatively opposite electrode tips being symmetrical, while adjacent electrode tips are opposite (the trigonometric functions differ by 180°). An electric quadrupole field is formed within the cavity due to the four electrode tips, and the trigonometric function modulation of the electrode tips creates a longitudinal electric field. Based on the characteristics of RFQ (Radial Matching Parameter) modulation, the RFQ can be divided into four segments: radial matching segment, shaping segment, beam focusing segment, and acceleration segment. The composition of each segment is mainly distinguished functionally based on the changes in pole modulation. In the radial matching segment, the focusing force increases from 0 to its maximum value over a relatively short distance, while the beam current is matched seamlessly with the time-varying focusing force. The focusing force is the effect of the electromagnetic field on the beam current. Since the electromagnetic field in the radial matching segment is time-harmonic and oscillates with time, such as an electric field E = E0e... iωtSimilar to the magnetic field, the focusing force also oscillates over time, just like the electromagnetic field. In the shaping section, the synchronous phase and longitudinal electric field are modulated. The synchronous phase increases from -90°, and the longitudinal electric field increases from 0, initially shaping the beam and preparing for focusing. The synchronous phase refers to the phase corresponding to the center of the beam in the electromagnetic field. At the RFQ inlet, the beam is continuous, equivalent to a synchronous phase of -90°. From the focusing section onwards, the beam is focused into a cluster, and the synchronous phase has a strict meaning. In the focusing section, the synchronous phase is further modulated until it reaches its final value, traditionally chosen as -30°. In the acceleration section, the synchronous phase no longer changes, while the pole head modulation is further increased to improve acceleration efficiency, accelerating the beam to the final required energy.

[0008] DTL (Drift Tube-to-Lift) is an accelerator structure consisting of a drift tube and an accelerating gap. When the relative velocity of protons β is between 0.1 and 0.1 (relative velocity β = v / c, where v is the proton velocity and c is the speed of light), DTL is the most suitable type of accelerator. Traditional DTL types, such as the Alvarez-type DTL, have a low acceleration gradient, resulting in a long acceleration tube for the same energy. Furthermore, this type of DTL requires the addition of a permanent magnet quadrupole within the drift tube, which is technically challenging, potentially leading to larger errors, and is difficult to adjust after fabrication. IH-DTL is a newer type of DTL. Its advantages include a high acceleration gradient, which can significantly reduce the DTL length. Simultaneously, the magnet does not need to be installed inside the drift tube, reducing manufacturing complexity. It also allows for a wider range of magnet selection, including electromagnetic quadrupoles, and allows for adjustments to address errors during actual commissioning and operation. IH-DTL primarily has two different designs. One approach is the KONUS (Kombinierte Null Grad Struktur) beam dynamics design. Existing KONUS-designed IH-DTLs are not designed for high operating frequencies, their structures are not compact enough, and their acceleration gradients are not high enough. The other approach is the APF (Alternating Phase Focusing) beam dynamics design. APF-based IH-DTLs have lower inlet acceptability and extremely high requirements for manufacturing errors and operational stability. If the inlet beam parameters deviate or there are structural errors, the outlet beam parameters will produce significant errors and fail to meet requirements.

[0009] Accelerators accumulate structural errors during manufacturing and assembly, requiring tuning rod adjustments to compensate for these errors and achieve target frequencies and field distributions. This process is called tuning. For RFQ and IH-DTL in proton injectors, existing tuning methods involve the following steps: measuring the longitudinal field distribution in each quadrant of the structure, comparing the measurement results with simulation calculations, then using the simulated microwave characteristics of the accelerator to determine the tuning rod adjustment amount, and iterating through these steps to complete the tuning. While existing methods offer various solutions for the tuning amount, they all rely on theoretical solutions derived from simulations. For injectors with relatively low frequencies, this can be achieved with several iterations. However, for higher-frequency proton injectors, due to their greater sensitivity, even small disturbances can cause significant errors. Therefore, using existing tuning methods requires more iterations, and may even fail to achieve the tuning target due to discrepancies between theoretical simulations and actual microwave performance. Summary of the Invention

[0010] The purpose of this invention is to provide a compact proton injector to solve the problem that there is currently a lack of low-energy proton accelerators as injectors in proton linear accelerators, thereby reducing the size, weight and construction cost of existing low-energy proton accelerators.

[0011] To achieve the above objectives, the present invention provides a compact proton injector, comprising an ion source system, an RFQ, and an IH-DTL connected in sequence, wherein the RFQ and IH-DTL operate at a frequency of 714 MHz, such that the total length of the RFQ and IH-DTL is less than 3 meters, and the beam output energy of the IH-DTL is higher than 8 MeV.

[0012] The operating frequencies of the RFQ and IH-DTL depend on the cavity cross-sectional area of ​​the RFQ and IH-DTL.

[0013] The IH-DTL includes a first periodic segment and a second periodic segment, with the first periodic segment directly connected to the RFQ through its 0-phase acceleration segment.

[0014] The length of the RFQ is less than 2 meters, and the beam output energy of the RFQ is higher than 4 MeV.

[0015] The first period segment only includes the 0-phase acceleration segment.

[0016] The compact proton injector is used in a linear accelerator.

[0017] The second periodic segment includes a matching segment, a beam-gathering segment, and a zero-phase acceleration segment arranged sequentially.

[0018] The beam-gathering section of the second periodic segment uses an acceleration unit with a synchronous phase of -35° or a synchronous phase of -60°.

[0019] The RFQ is divided into a radial matching section, a shaping section, a beam-gathering section, and an acceleration section. The final value of the synchronization phase of the beam-gathering section of the RFQ is -20°.

[0020] The beam aperture of the RFQ is between 0.8 and 1 mm to improve beam transmission efficiency.

[0021] The compact proton injector of this invention meets the injection requirements of proton linear accelerators and can serve as an injector for a wide range of proton accelerators, providing a high-quality beam. By setting the operating frequency to 714MHz, the compact injector achieves an acceleration gradient of 2MV / m for the RFQ and an effective acceleration gradient of 9MV / m for the IH-DTL. This results in a total length of less than 3 meters for the RFQ and IH-DTL (approximately 4 meters including the ion source), thereby reducing the injector's size and weight, lowering construction costs, and enabling its application in various medical proton devices. This promotes the widespread use of medical proton devices and has a positive impact on the medical applications of protons (such as flash therapy and boron neutron capture therapy (BNCT)).

[0022] The compact proton injector of this invention comes in two designs: one with a shorter length and a final energy higher than 8 MeV; the other with a final energy higher than 10 MeV, and correspondingly a longer length. Both designs achieve a transmission efficiency of over 50%.

[0023] This invention can not only meet the injection requirements of linear accelerators and promote the development of flash therapy, but also meet the injection requirements of most other types of medical accelerators. Attached Figure Description

[0024] Figure 1A and Figure 1B This is a general structural layout diagram of the compact proton injector of the present invention, wherein, Figure 1A A compact proton injector with an output energy of 8 MeV is shown. Figure 1B A compact proton injector with an output energy of 10 MeV is shown.

[0025] Figure 2 This is a cross-sectional view along the length of the RFQ of the compact proton injector of the present invention.

[0026] Figure 3 This is a three-section schematic diagram of the RFQ of the compact proton injector of the present invention, wherein the z-axis is the length direction of the RFQ, and the x-axis and y-axis are the cross-sectional directions of the RFQ.

[0027] Figure 4This is a schematic diagram of the structure of the IH-DTL compact proton injector of the present invention.

[0028] Figure 5A and Figure 5B This is a schematic diagram of the installation of the tuner and coupler of the compact proton injector of the present invention. Detailed Implementation

[0029] Combined with appendix Figures 1A to 5B The present invention provides preferred embodiments, which are described in detail below.

[0030] like Figure 1A and Figure 1B As shown, the compact proton injector of the present invention is applied to a proton linear accelerator, which includes an ion source system 100, an RFQ (Radio Frequency Quadruple) 200, an IH-DTL (Interdigital H-mode Drifting Tube Linac) 300, and a matching section 301 disposed inside the IH-DTL 300, connected in sequence.

[0031] The main improvement of this invention lies in the compact RFQ and IH-DTL. Structurally, the main difference is that the cavity cross-sectional area is smaller, corresponding to a higher operating frequency.

[0032] The ion source system 100 includes an ion source 101 and a low-energy transmission line (LEBT) 102.

[0033] Ion source 101 is the device that generates protons and is the source of the entire accelerator system, providing the accelerator with a proton beam of sufficient flux. Ion source 101 is preferably a compact 2.45 GHz ECR ion source with an all-permanent magnet structure.

[0034] LEBT 102 is configured to focus and transmit the beam so that the beam can be injected into RFQ 200 with the emittance required to meet the RFQ 200 inlet requirements.

[0035] Thus, protons are first generated by ion source 101 (Figure 1). Hydrogen gas is introduced into ion source 101 through the gas injection port and microwave input port, and microwave power is fed in. The hydrogen gas forms plasma at the electrode positions, and the protons are separated and extracted using a high extraction voltage with an extraction energy of 50 keV. The protons are then focused during transmission via a low-energy transmission line (LEBT), and then leave the ion source system and enter RFQ 200.

[0036] like Figure 2 and Figure 3As shown, the RFQ 200 is an acceleration structure invented to address the characteristics of proton beams at low energies. It primarily utilizes four electrodes to generate a strong focusing effect, solving the problem of proton beam emittance growth at low energies. Simultaneously, modulation is added to the electrode tip to produce an acceleration effect. In this invention, the RFQ 200 is a four-wing type. Based on the characteristics of RFQ electrode modulation, the RFQ can be divided into four segments: radial matching segment, shaping segment, beam focusing segment, and acceleration segment. The radial matching segment is designed to provide focusing force that increases from 0 to its maximum value over a short distance, allowing the beam to match the time-varying focusing force without loss. The shaping segment modulates the synchronization phase and longitudinal electric field, increasing the synchronization phase from -90° and the longitudinal electric field from 0 to initially shape the beam and prepare for beam focusing. The beam focusing segment further modulates the synchronization phase until it reaches its final value. The acceleration segment maintains the synchronization phase at its final value, ensuring the electrode modulation parameters remain essentially constant at maximum modulation, thereby improving acceleration efficiency and accelerating the beam to its final energy. The RFQ's electrode tip has a trigonometric function-like shape, which can be understood as a "wave". The modulation parameters of the electrode tip determine the amplitude of the "wave".

[0037] Thus, the protons leave the ion source system as a continuous beam. First, they enter the radial matching section of the RFQ, where the accelerator aperture rapidly narrows, modulating the beam's lateral shape to enter the acceptability range. In the shaping section, the modulation of the electrode tip gradually increases from 0, and the continuous beam begins to slowly converge into a cluster. In the focusing section, the modulation of the electrode tip further increases to its maximum value, and the beam is further focused, with its lateral and longitudinal phase space distributions exhibiting periodic oscillations. Finally, the beam enters the acceleration section, where the electrode tip maintains essentially its maximum modulation, and the beam's synchronization phase remains constant at its final value, primarily used for beam acceleration.

[0038] As described above, the structure of the RFQ 200 in this invention is basically the same as that of the existing quad-wing RFQ. The differences between the RFQ 200 of this invention and the existing quad-wing RFQ are: 1) The RFQ operates at a higher frequency, thus achieving a higher acceleration gradient. 2) The final value of the synchronization phase of the beam-focusing section is -20°. This phase selection allows for a higher acceleration gradient, resulting in higher output energy and a shorter length. 3) The beam aperture size of the RFQ is between 0.8 and 1 mm. Therefore, the length of the RFQ 200 is less than 2 meters, achieving a compact design while ensuring that the beam output energy of the RFQ is still higher than 4 MeV. In this embodiment, the length of the RFQ 200 is approximately 2 meters, and the beam is accelerated to above 4 MeV within the approximately 2-meter length of the RFQ 200.

[0039] Based on Kilpatrick theory and empirical formulas It can be seen that the higher the frequency, the higher the surface field the structure can withstand without arcing, and the stronger the field inside the cavity, the stronger the electric field that can be used for acceleration. Because higher operating frequencies allow accelerating structures (such as RFQ and IH-DTL) to withstand higher electromagnetic fields, this increases the acceleration gradient of the accelerator and shortens the length of the injector in this invention. The acceleration gradient refers to the beam energy gain divided by the accelerator length, G = E / L. In RFQ, this is the beam energy gain divided by the total length of the RFQ; in IH-DTL, the beam energy gain divided by its total length can be called the effective acceleration gradient. Here, the effective acceleration gradient is used for IH-DTL, while the acceleration gradient in the 0-phase acceleration segment can be higher, but it has no practical significance. Therefore, the higher operating frequency of RFQ allows for a higher acceleration gradient (reaching 2MV / m), enabling the proton beam to be accelerated to higher output energies over a shorter length. At higher output energies, the space charge effect of the proton bundle is reduced, making it easier to accelerate and focus. Consequently, higher beam quality can be achieved during subsequent IH-DTL acceleration, improving the overall transmission efficiency of the injector.

[0040] In this embodiment, the increased operating frequency of the RFQ 200 of the present invention is achieved by reducing the cross-sectional area of ​​the cavity in its structure. Specifically, the cross-sectional area of ​​the RFQ 200 of the present invention can be expressed as the inner diameter of the cavity. In the present invention, the inner diameter (diameter) is less than 15 cm, while existing ones are generally above 20 cm, with some reaching about 1 meter. Furthermore, the length of the RFQ 200 of the present invention is 1.98 meters, with a relatively small variable range, approximately a few centimeters, to achieve a compact design. Existing RFQs have a wide range of lengths, from tens of centimeters to five or six meters. RFQs commonly used as injectors with energies around 3 MeV are generally between 2.5 meters and 4 meters in length.

[0041] The operating frequency of the RFQ in this invention differs from commonly used RFQ frequencies such as 325MHz and 425MHz. The operating frequency of the RFQ in this invention is 714MHz, which is higher than existing RFQ frequencies, achieving higher output energy. The output energy of the RFQ is above 4MeV, with an output energy range of approximately 4-4.2MeV, higher than the output energy of existing proton RFQs (below 3.5MeV).

[0042] The compact proton injector of this invention is designed to inject a suitable beam into a proton linear accelerator. The frequency required for the beam in a linear accelerator is a factor of its operating frequency, meaning the operating frequency of the linear accelerator is an integer multiple of the injector's frequency. Therefore, the higher operating frequency of the RFQ in this invention satisfies the injection requirements of the subsequent linear accelerator, while also increasing the acceleration gradient of the RFQ, reducing the size and weight of the proton injector, and thus lowering construction costs. Other types of medical proton accelerators, mainly cyclotrons and synchrotrons, do not have frequency requirements for the injector; therefore, the compact proton injector of this invention can also be used as an injector for other types of accelerators.

[0043] The main reasons why existing technologies do not utilize this frequency of RFQ are as follows: First, as mentioned earlier, existing medical proton accelerators are all of the two types: cyclotron accelerators and synchrotron accelerators. These two types of accelerators do not have requirements on the operating frequency of the injector, and the technology for lower frequency RFQs is relatively mature. Therefore, there is no need to develop high operating frequency RFQs, while this invention is based on linear accelerators. Second, although high operating frequencies bring the advantage of high acceleration gradients to RFQs, they also face the risk of increased surface field and increased cavity arcing rate, which places higher demands on structural design and manufacturing processes. Furthermore, high-frequency RFQs require trade-offs in output energy, length, and transmission efficiency. Too low an output energy will lose the advantage of high frequency, and too long a length will increase the difficulty of manufacturing and tuning. Based on this, the output energy of the RFQ in this invention is selected to be a suitable 4MeV, ensuring that transmission efficiency is not sacrificed too much when the length is relatively short.

[0044] In this invention, the RFQ operates at a higher frequency; therefore, a smaller beam aperture is used to address the decrease in focusing factor caused by the higher frequency. The circle formed by the four electrodes of the RFQ is called the beam aperture. Existing RFQ designs typically have beam apertures greater than 1 mm, usually ranging from 1.5 to 3 mm. In this invention, the RFQ beam aperture is less than 1 mm, with a reasonable range of 0.8 to 1 mm, meaning the radius of the circle formed by the electrodes is less than 1 mm. Reducing the beam aperture increases the electromagnetic field strength near the electrodes, correspondingly improving the focusing factor of the structure. This improved focusing effect enhances beam transmission efficiency.

[0045] In this invention, the operating frequency of the IH-DTL 300 is also 714MHz. The beam dynamics design of the IH-DTL 300 is based on the KONUS scheme. The basic structure of the existing KONUS scheme IH-DTL 300 includes: a 0-phase acceleration section, a focusing section, and a beam-closing section, which are used to accelerate and change the beam shape, respectively. In the classic KONUS design, the phase of the beam-closing section is generally -35°.

[0046] like Figure 4 As shown, the IH-DTL includes a first periodic segment and a second periodic segment. The second periodic segment of the IH-DTL has a matching segment (i.e., a focusing segment) at one end near the first periodic segment. The first and second periodic segments use an integrated design, which can improve the stability of the cavity, reduce the difficulty of collimation between the two cavity segments, and reduce errors.

[0047] In this invention, the improvements to the IH-DTL 300 based on the KONUS scheme are mainly reflected in the following aspects: 1) The focusing and beam-gathering segments of the first cycle are eliminated, that is, the first cycle segment of the IH-DTL is directly connected to the RFQ through its 0-phase acceleration segment. Preferably, the first cycle segment only includes the 0-phase acceleration segment; 2) The second cycle segment of the IH-DTL can use either the existing -35° synchronization phase or the -60° synchronization phase.

[0048] In existing technologies, a matching segment is typically required between the RFQ and the IH-DTL. In this invention, the first cycle segment of the RFQ and IH-DTL is directly connected, eliminating the matching segment usually required between the RFQ and IH-DTL. Consequently, by eliminating this matching segment, the entire injector structure becomes more compact and shorter in length.

[0049] The matching section serves to adjust the beam shape in phase space. In this invention, the beam exhibits extremely high beam quality before and after the first period of the IH-DTL (i.e., for the RFQ, its output energy is high, the beam's space charge effect is small, and the beam maintains a low emittance before the first period of the IH-DTL after passing through the RFQ; at higher energies, the space charge effect of the proton beam decreases, making it easier to accelerate and focus, resulting in better beam quality during the subsequent IH-DTL acceleration process, thereby improving transmission efficiency; for the IH-DTL, the first period of the IH-DTL is designed to be relatively short, between 20-25 cm, so the beam does not diverge quickly during acceleration in this section). This ensures a compact design while maintaining high transmission efficiency. The high beam quality and the lower beam current requirements during proton therapy allow for the elimination of a matching section between the RFQ and IH-DTL, and the elimination of a focusing section in the first IH-DTL, while simultaneously achieving the injector design goals, resulting in a shorter and more compact accelerator.

[0050] The reason for the lower beam current requirement in this invention is that the beam current requirement of linear accelerators differs from that of other types of accelerators. As mentioned above, the starting point of this invention is as an injector for proton linear accelerators. The main body of the proton linear accelerator can operate continuously simultaneously with the injector. Therefore, the beam current required for medical use of proton linear accelerators is relatively low, typically in the hundreds of μA range. Other types (cyclotrons, synchrotrons), due to their different acceleration methods, require the entire beam to be injected into the main accelerator first. To increase the current intensity in the main accelerator and save injection time, a higher injection current intensity is required.

[0051] In this invention, the first periodic segment of the IH-DTL corresponds to the reduction of the matching segment (i.e., the focusing segment in each periodic segment of the IH-DTL300 based on the KONUS scheme) and the elimination of the beam-gathering segment. Therefore, the first periodic segment of the IH-DTL only includes a 0-phase acceleration segment. The acceleration gradient of the 0-phase acceleration structure is higher than that of the beam-gathering segment. This design can improve the equivalent acceleration gradient of the IH-DTL and shorten the injector length. Furthermore, due to the compact design described above, it still meets the accelerator's requirements for the injector. The acceleration gradient of the 0-phase acceleration segment is higher than that of the beam-gathering segment, thus improving the overall acceleration gradient of the IH-DTL and shortening the injector length.

[0052] In this invention, the second periodic segment of the IH-DTL is a complete periodic structure based on the KONUS scheme. That is, the second periodic segment of the IH-DTL is not significantly different from existing technologies except for the operating frequency. It includes a matching segment, a focusing segment, and a zero-phase acceleration segment arranged sequentially. The matching segment, composed of three electromagnets, is used to change the beam distribution in phase space, altering the lateral movement trend of the beam to focus.

[0053] There are two schemes for the second period segment of IH-DTL.

[0054] According to a first embodiment of the present invention, the focusing segment of the second periodic section of the IH-DTL uses a conventional accelerating unit with a synchronous phase of -35°, and the total length of the RFQ and IH-DTL is less than 3 meters, thereby accelerating the proton beam to 8 MeV over a shorter distance. In this embodiment, the lengths of both the focusing segment and the 0-phase accelerating segment are the same as in the prior art, the length of the first periodic section is 20-25 cm, the length of the second periodic section is 35-40 cm, and the final output energy is higher than 8 MeV.

[0055] According to a second embodiment of the present invention, the focusing segment of the second periodic segment of the IH-DTL adopts an acceleration unit with a synchronous phase of -60°. This scheme allows the cavity length to be increased (i.e., the lengths of both the focusing segment and the 0-phase acceleration segment will change, but the length change is mainly reflected in the 0-phase acceleration segment). The length of the first periodic segment is 20-25cm, the length of the second periodic segment is 50-60cm, the total length of the RFQ and IH-DTL is less than 3 meters, and the final beam output energy is higher than 10MeV, that is, the proton beam can be accelerated to 10MeV.

[0056] Both schemes have a transmission efficiency of over 50%.

[0057] For IH-DTL, the beam is not accelerated in the focusing section. In the focusing section and the zero-phase acceleration section, the acceleration gradient G can be used... To indicate, among which, For synchronization phase, G0 is the gradient constant. In similar structural designs, G0 can be considered a constant, and G0 is positively correlated with the operating frequency. Synchronization phase in the 0-phase acceleration segment. In the focusing section, this invention relates to two phases, -35° and -60°, thus the acceleration gradient in the 0-phase acceleration section is higher than that in the focusing section. By eliminating the non-accelerating focusing section and the focusing section with a lower acceleration gradient, the equivalent acceleration gradient of the entire IH-DTL is increased. In this invention, because the focusing and focusing sections are eliminated in the first periodic section of the IH-DTL, and because the higher operating frequencies of RFQ and IH-DTL allow for higher electromagnetic field strengths, a higher acceleration gradient is achieved for RFQ and IH-DTL, making the entire injector structure more compact and shorter in length.

[0058] Higher operating frequencies in accelerators often lead to lower transmission efficiency, but the proton injector in this invention maintains high transmission efficiency. Higher transmission efficiency allows for higher output proton beam intensity, meeting the needs of more high-current applications. On one hand, a smaller beam aperture is used in the RFQ, correspondingly increasing the focusing factor of the structure. Improved focusing effect enhances transmission efficiency. On the other hand, the RFQ outputs higher energy; in this invention, the RFQ output energy exceeds 4 MeV. At higher energies, the space charge effect of the proton beam decreases, making it easier to accelerate and focus. This results in better beam quality during subsequent IH-DTL acceleration, further improving transmission efficiency.

[0059] In the IH-DTL, the focusing section uses a quadrupole magnet in the form of a permanent magnet to focus the beam and improve the lateral shape of the beam. In this invention, the focusing section also uses a quadrupole magnet in the form of an electromagnet to ensure better focusing effect.

[0060] Each periodic segment of the RFQ and IH-DTL is fed with power using a magnetic coupler, enabling independent phase adjustment for both. Specifically, the RFQ and IH-DTL are connected to their respective magnetic couplers, which are connected to a power source via coaxial cables. Thus, RF power is generated from the power source, transmitted to the magnetic coupler via the coaxial cable, and then used by the ring probe of the magnetic coupler to excite the electromagnetic field within the cavity. This design allows for greater flexibility in the matching segment length within the IH-DTL dual-cavity configuration, freeing it from the constraints of beam synchronization phase requirements. Existing technologies typically place several KONUS periodic structures within a large cavity, fed with power through a single coupler. This necessitates that the matching segment length meet certain conditions to satisfy the beam synchronization phase requirements. The relationship can be roughly expressed as: L = L0 + kλ, where L0 is the minimum length determined by the beam synchronization phase difference before and after the matching segment, k is a positive integer, and λ is the microwave wavelength. It is evident that the matching segment length varies in units of microwave wavelength, limiting its flexibility. Power is fed in through two couplers, and the phase of the fed microwave can be controlled by the couplers. Therefore, regardless of the length of the matching section, the synchronous phase requirement of the beam can be met by adjusting the phase of the fed microwave.

[0061] like Figure 5A and Figure 5B As shown, the cavity walls of RFQ and IH-DTL are provided with openings for the insertion of tuner 501 and coupler 502. The tuner is inserted into these openings for tuning. For RFQ, tuners are present in all four directions (up, down, left, and right), while couplers are only present on one or two of these surfaces. For IH-DTL, tuners are present on only two surfaces (left and right), and couplers are present on one of these surfaces. In this invention, the tuner has a corresponding mechanical adjustment structure. The tuner controls the insertion depth of the tuning rod through this mechanical adjustment structure, enabling reciprocating adjustment. Furthermore, the mechanical adjustment structure includes a matching nut and a screw. By adjusting the screw with the nut, the screw drives the tuning rod into the cavity of RFQ and IH-DTL, allowing precise control of the tuning rod's insertion depth and enabling higher-precision tuning of the cavity. This achieves high precision and reciprocating capability for the tuner.

[0062] Because various errors occur during the machining, assembly, and welding processes of machines, the cavity ultimately needs to be tuned to achieve optimal performance. In proton injectors, existing technologies generally use tuning rods for tuning. The tuning rod is inserted into the cavity through a hole in the cavity wall, and the microwave performance of the cavity is changed by controlling the insertion depth of the tuning rod, thus achieving the tuning purpose. The current approach involves machining a tuning rod of a certain length, calculating the required insertion depth of the tuning rod through tuning experiments, and then calculating the length of the tuning rod outside the cavity. After several iterative experiments, the final parameters are determined, and the tuning rod is cut to the required length. This tuning method has low precision and poor repeatability. Different people will produce different errors in their measurements. Furthermore, because the tuning rod needs to be cut to the desired insertion depth, it can only be shortened, not lengthened, making it difficult to correct errors during tuning. Additionally, existing technologies have poor tuning precision. While high-precision measuring tools like calipers can be used to determine the insertion depth by measuring the length of the tuning rod outside the cavity, the accumulated measurement error is significant due to manufacturing errors in the tuning rod and its movement during adjustment. Repeatability is also poor, with different people obtaining different results. This invention, through the aforementioned mechanical adjustment structure, achieves high precision and reciprocating capability in the tuner, thus improving tuning accuracy.

Claims

1. A compact proton injector, comprising an ion source system, an RFQ, and an IH-DTL connected in sequence, characterized in that, The RFQ and IH-DTL operate at a frequency of 714MHz, which makes the total length of the RFQ and IH-DTL less than 3 meters, and the beam output energy of the IH-DTL is higher than 8 MeV. The IH-DTL includes a first periodic segment and a second periodic segment. The first periodic segment is directly connected to the RFQ through its 0-phase acceleration segment. The length of the RFQ is less than 2 meters, and the beam output energy of the RFQ is higher than 4 MeV. The first periodic segment only includes the 0-phase acceleration segment. The second periodic segment includes a matching segment, a beam-focusing segment, and a zero-phase acceleration segment arranged sequentially; the beam-focusing segment of the second periodic segment uses an acceleration unit with a synchronous phase of 0° or 0°; the RFQ is divided into a radial matching segment, a shaping segment, a beam-focusing segment, and an acceleration segment, and the final value of the synchronous phase of the beam-focusing segment of the RFQ is -20°; the beam aperture size of the RFQ is 0.8-1 mm to improve the beam transmission efficiency.

2. The compact proton injector according to claim 1, characterized in that, The operating frequencies of the RFQ and IH-DTL depend on the cavity cross-sectional area of ​​the RFQ and IH-DTL.

3. The compact proton injector according to claim 1, characterized in that, The compact proton injector is used in a linear accelerator.

Images