Low acceleration voltage radio frequency cavity

Abstract

This invention discloses a low-accelerating-voltage radio frequency (RF) cavity, belonging to the field of particle accelerator technology. The RF cavity includes a standing-wave resonant cavity, with its core improvement lying in the periodic arc-shaped corrugated structure on the surface of the inner conductor, and the inner conductor surface being coated with a 5-10 nm thick TiN thin film. This invention disrupts the resonance conditions for secondary electron multiplication through the periodic corrugated structure, while simultaneously utilizing the TiN thin film to reduce the secondary electron yield on the inner conductor surface. The synergistic effect of these two methods achieves highly efficient suppression of the secondary electron multiplication effect with minimal impact on the cavity's RF performance. This low-accelerating-voltage RF cavity has a simple structure and reliable operation, effectively improving the stability and reliability of cavity operation. It is particularly suitable for the focusing cavity of petal accelerators, significantly improving beam quality and reducing beam loss.

Description

Technical Field

[0001] This invention relates to the field of particle accelerator technology, and more specifically to a low accelerating voltage radio frequency cavity. Background Technology

[0002] Radio frequency (RF) resonant cavities are the core components of particle accelerators. They accelerate and control the beam quality by interacting with charged particles through an internally excited RF electromagnetic field of a specific frequency. Low-accelerating-voltage (LAV) RF cavities are crucial devices in the beam injection stage, and their performance directly determines the beam quality and operational stability of the subsequent accelerator system. However, LAV RF cavities face a severe challenge from the secondary electron multiplication effect during operation. When the frequency and intensity of the RF electric field within the cavity meet specific conditions, electrons repeatedly collide with adjacent material surfaces, exciting even more secondary electrons. This leads to an exponential increase in the number of electrons, resulting in a series of problems such as RF power loss, increased cavity thermal load, decreased vacuum, and deteriorated beam quality, all of which affect the reliable operation of the accelerator. Currently, the main methods for suppressing secondary electron multiplication at home and abroad include low SEY (Secondary Electron Yield, SEY) material coating, surface morphology modification, and particle beam irradiation treatment. However, these methods all have obvious limitations. Using low SEY coating alone has the problems of limited application on complex curved surfaces and poor long-term stability. Moreover, it can only reduce the generation of secondary electrons at the source and cannot destroy the resonance trajectory of the generated electrons. Using surface morphology modification alone is prone to electric field distortion and can only destroy some electron resonance trajectories. It cannot fundamentally reduce the number of secondary electrons generated. The two technical means do not form a synergistic effect and it is difficult to fundamentally solve the problem of secondary electron multiplication in low accelerating voltage radio frequency cavities. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the purpose of this invention is to provide a low-acceleration-voltage radio frequency cavity. This low-acceleration-voltage radio frequency cavity has a simple structure and reliable operation, and can effectively improve the stability and reliability of cavity operation.

[0004] To achieve the above objectives, the embodiments of this invention provide the following technical solutions:

[0005] This application provides a low accelerating voltage radio frequency cavity, including a standing wave resonator cavity. The cavity is characterized in that the inner conductor surface of the standing wave resonator cavity has a periodic corrugated structure with a circular arc cross-section, and the inner conductor surface is coated with a TiN thin film with a thickness of 5-10 nm.

[0006] Furthermore, the standing wave resonant cavity is a quarter-wavelength resonant cavity composed of an inner and outer conductor coaxial structure.

[0007] Furthermore, the inner conductor has a tapered structure, and the diameter of the open-circuit end of the inner conductor is smaller than the diameter of the short-circuit end.

[0008] Furthermore, the periodic corrugated structure is disposed within a range of 48mm to 653mm axial distance from the open end of the inner conductor, and the depth of the periodic corrugated structure is 1-5mm, the width is 4-8mm, and the spacing between adjacent corrugations is 1-3mm.

[0009] Furthermore, the TiN thin film is prepared using magnetron sputtering technology.

[0010] Furthermore, it also includes an input coupler, which is a ring-shaped magnetic coupling structure used to feed radio frequency power into the standing wave resonant cavity.

[0011] Furthermore, it also includes a radio frequency (RF) signal pickup unit used to detect the amplitude and phase of the RF field within the standing wave resonant cavity.

[0012] Furthermore, it also includes a manual tuner for adjusting the resonant frequency of the radio frequency cavity.

[0013] Furthermore, the standing wave resonator also includes a vacuum pipe disposed outside the standing wave resonator and communicating with the inside of the standing wave resonator.

[0014] Furthermore, the low accelerating voltage radio frequency cavity is used as the focusing cavity of the petal accelerator, and the resonant frequency of the focusing cavity is 107.5MHz.

[0015] The beneficial effects of this invention are as follows: By combining a circular arc-shaped periodic corrugated structure with a 5-10 nm thick TiN thin film and applying it to the surface of the conductor inside a low-acceleration-voltage radio frequency cavity, a dual synergistic suppression of the secondary electron multiplication effect is achieved. The periodic corrugated structure alters the trajectory of electrons through physical scattering, disrupting the resonance conditions for secondary electron multiplication; the TiN thin film directly reduces the yield of secondary electrons on the surface of the inner conductor, reducing the number of secondary electrons generated during each electron collision at the source. The synergistic effect of both achieves a superior suppression effect compared to a single technique. Furthermore, because the periodic corrugated structure is only located in the region prone to secondary electron multiplication, and the TiN thin film is extremely thin, its impact on the cavity's radio frequency performance is minimal, and it does not cause significant electric field distortion or increased power loss. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a low-acceleration-voltage radio frequency cavity provided in an embodiment of this application;

[0017] Figure 2 for Figure 1 A schematic diagram of the cross-sectional structure along the AA plane in the middle;

[0018] Figure 3 for Figure 1 A schematic diagram of the right-side view structure;

[0019] Figure 4 This is a schematic diagram of a low-acceleration-voltage radio frequency cavity provided in an embodiment of this application;

[0020] Figure 5 for Figure 4 A schematic diagram of the cross-sectional structure along the HH plane.

[0021] Reference numerals: 1-Outer conductor, 2-Periodic corrugated structure, 3-Inner conductor, 4-Input coupler, 5-Beam conduit, 6-RF signal pickup, 7-Manual tuner. Detailed Implementation

[0022] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the present invention.

[0023] In this invention, the terms "system" and "network" are used interchangeably. "Multiple" refers to two or more; therefore, in this invention, "multiple" can also be understood as "at least two." "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. Additionally, the character " / ", unless otherwise specified, generally indicates that the preceding and following related objects have an "or" relationship. Furthermore, it should be understood that in the description of this invention, terms such as "first" and "second" are used only for descriptive purposes and should not be construed as indicating or implying relative importance or order.

[0024] like Figures 1-5 As shown, this application provides a low accelerating voltage radio frequency cavity, including a standing wave resonant cavity. The cavity is characterized in that the inner conductor 3 of the standing wave resonant cavity has a periodic corrugated structure 2 on its surface. The cross-section of the periodic corrugated structure 2 is arc-shaped, and the inner conductor 3 is coated with a TiN thin film with a thickness of 5-10 nm. The TiN thin film is prepared by magnetron sputtering technology.

[0025] In another possible embodiment, a periodic arc-shaped corrugated structure is first fabricated on the outer surface of the inner conductor 3 of the standing wave resonant cavity using CNC machining equipment. This structure allows electrons incident on the surface to undergo multiple scatterings on arc surfaces with different curvatures, resulting in random changes in their motion direction and energy. This prevents them from meeting the resonance conditions required for secondary electron multiplication, thereby disrupting the stable cycle of secondary electron multiplication. Subsequently, a TiN thin film with a thickness precisely controlled to 5-10 nm is deposited on the entire outer surface of the inner conductor 3. TiN is a ceramic material with metallic conductivity, and its secondary electron yield is much lower than that of commonly used cavity materials such as oxygen-free copper, typically less than 1.5. This significantly reduces the number of secondary electrons generated during each electron collision, thereby reducing the probability of secondary electron multiplication at its source. By combining the physical scattering effect of the periodic corrugated structure 2 with the TiN thin film, the secondary electron multiplication effect is effectively suppressed, ensuring stable operation of the cavity under low accelerating voltage conditions.

[0026] By combining a circularly shaped periodic corrugated structure 2 with a 5-10 nm thick TiN film and applying it to the surface of the conductor 3 inside a low-acceleration-voltage RF cavity, a dual synergistic suppression of the secondary electron multiplication effect is achieved. The periodic corrugated structure 2 alters the trajectory of electrons through physical scattering, disrupting the resonance conditions for secondary electron multiplication and preventing the continuous accumulation of electrons on the surface. The TiN film, on the other hand, reduces the secondary electron yield on the surface of the conductor 3, decreasing the number of secondary electrons generated during each electron collision at the source. Together, they achieve a superior suppression effect compared to a single technique. Furthermore, since the periodic corrugated structure 2 is only placed in the region prone to secondary electron multiplication, and the TiN film is extremely thin, its impact on the cavity's RF performance is minimal, and it does not cause significant electric field distortion or increased power loss.

[0027] In the embodiments of this application, the standing wave resonant cavity is a quarter-wavelength resonant cavity composed of an inner and outer conductor coaxial structure.

[0028] In another possible embodiment, the operating wavelength is determined based on the operating frequency, and the total length of the cavity is designed to be one-quarter of the wavelength. A cylindrical outer conductor 1 and a tapered inner conductor 3 are fabricated, and the inner conductor 3 is fixed to the end face of the outer conductor 1 by welding or bolting to form a coaxial structure; the other end of the inner conductor 3 is an open-circuit end. When the radio frequency signal is fed into the cavity through the input coupler 4, it will excite an axially propagating electromagnetic wave in the annular space between the inner and outer conductors. The electromagnetic wave undergoes total reflection at the open-circuit end and superimposes with the incident wave to form a standing wave. The maximum electric field strength occurs at the open-circuit end of the inner conductor 3, which is the area through which the beam passes, and can provide an effective accelerating electric field for charged particles. The maximum magnetic field strength occurs at the short-circuit end. This electromagnetic field distribution is highly matched with the operating requirements of the low-accelerating voltage radio frequency cavity, and can obtain sufficient accelerating electric field strength at a low input power to meet the requirements of beam pre-acceleration or focusing.

[0029] In the embodiments of this application, the inner conductor 3 has a tapered structure, and the diameter of the open end of the inner conductor 3 is smaller than the diameter of the short-circuit end.

[0030] In another possible embodiment, the inner conductor 3 is a conical structure integrally machined, with an open-circuit diameter of 60 mm and a short-circuit diameter of 90 mm. This conical structure can effectively reduce the current density at the short-circuit end, reduce ohmic losses, and thus improve the quality factor of the cavity. In addition, the conical inner conductor 3 has higher mechanical strength, can better withstand the stress during processing and operation, and enhance the structural stability of the cavity.

[0031] In the embodiments of this application, the periodic corrugated structure 2 is disposed within the range of 48mm to 653mm axial distance from the open end of the inner conductor 3. The periodic corrugated structure 2 has a depth of 1-5mm, a width of 4-8mm, and a spacing of 1-3mm between adjacent corrugations.

[0032] In another possible embodiment, the electric field distribution within the radio frequency cavity is first calculated using three-dimensional electromagnetic field simulation software. Electron tracking simulation is then performed based on this electric field distribution. According to the trend of electron number variation, the region from 48mm to 653mm axially from the open-circuit end of the inner conductor is identified as a region prone to secondary electron multiplication. Subsequently, a periodic circular arc-shaped corrugated structure is machined within this region using a CNC milling machine. Each corrugation has a depth of 3mm, a width of 6mm, and a spacing of 2mm between adjacent corrugations. This parameter setting causes electrons, upon incident on the corrugated surface, to undergo multiple scatterings on the arc surfaces with different curvatures. Their direction of motion and energy exhibit random variations, thus failing to meet the resonance conditions required for secondary electron multiplication, ultimately completely disrupting the stable cycle of the secondary electron multiplication effect.

[0033] In the embodiments of this application, the low accelerating voltage radio frequency cavity further includes an input coupler 4, which is a ring magnetic coupling structure used to feed radio frequency power into the standing wave resonant cavity.

[0034] In another possible embodiment, the annular magnetic coupling structure consists of a coupling ring and a coaxial transmission line. The inner conductor of the coaxial transmission line is welded to one end of the coupling ring, and its outer conductor is sealed to the cavity housing via a flange to maintain the vacuum seal of the cavity. When a radio frequency (RF) signal is transmitted to the coupling ring via the coaxial transmission line, an alternating magnetic field is generated around the coupling ring. This alternating magnetic field couples with the standing wave magnetic field inside the cavity, thereby feeding RF power from the external transmission line into the cavity. By adjusting the rotation angle of the coupling ring, the coupling degree can be changed to achieve impedance matching between the cavity and the external transmission line, ensuring efficient transmission of RF power.

[0035] In embodiments of this application, a radio frequency signal pickup 6 is also included, which is used to detect the amplitude and phase of the radio frequency field within the standing wave resonant cavity.

[0036] In another possible embodiment, the RF signal pickup 6 employs a small electrical probe structure, consisting of an oxygen-free copper probe and a vacuum penetration element. The probe is installed within an interface on the side wall of the cavity's central portion, with one end extending into the cavity and coupling with the electric field, and the other end connected to an external signal processing circuit via the vacuum penetration element. When an RF electric field exists within the cavity, the probe induces an electrical signal proportional to the electric field strength and in phase with it. By detecting the amplitude and phase of this signal, the parameters of the RF field within the cavity can be obtained in real time. The probe is positioned in a region of moderate electric field strength in the central portion of the cavity, ensuring sufficient signal sensitivity while avoiding significant interference with the electric field distribution. During operation, the signal processing circuit converts the RF signal into a digital quantity and transmits it to the control system. The control system then adjusts the output power of the RF source in real time to maintain the stability of the RF field within the cavity.

[0037] By setting up the radio frequency signal pickup 6, the amplitude and phase of the radio frequency field inside the cavity can be monitored in real time, providing accurate signals for the feedback control of the radio frequency source.

[0038] In embodiments of this application, a manual tuner 7 is also included, which is used to adjust the resonant frequency of the radio frequency cavity.

[0039] In another possible embodiment, the manual tuner 7 adopts a screw-type structure, mainly composed of a tuning rod, a screw, a handle, and a sealing flange. The tuning rod is made of oxygen-free copper. The tuner is installed in the tuner interface on the side wall of the cavity through the sealing flange to ensure the vacuum seal of the cavity. One end of the tuning rod extends into the cavity, and the other end is connected to the screw. A handle is installed at the end of the screw. Rotating the handle can drive the screw to rotate, thereby driving the tuning rod to move axially to change its depth into the cavity.

[0040] The portion of the tuning rod that extends into the cavity alters the electromagnetic field distribution within the cavity, thereby adjusting the resonant frequency. Specifically, as the depth of insertion increases, the resonant frequency of the cavity decreases; conversely, as the depth decreases, the frequency increases. The tuner's adjustment range is designed to be 300Hz, sufficient to cover frequency shifts caused by manufacturing errors and temperature variations, ensuring the cavity always operates in a resonant state and improving power transmission efficiency.

[0041] In an embodiment of this application, the low accelerating voltage radio frequency cavity is used as the focusing cavity of the petal accelerator, and the resonant frequency of the focusing cavity is 107.5MHz.

[0042] In another possible embodiment, the low accelerating voltage RF cavity of the present invention is used as the focusing cavity of a petal accelerator. The resonant frequency of this focusing cavity is 107.5 MHz, which is consistent with the main accelerating frequency of the petal accelerator, and the total length of the cavity is 906 mm. The inner conductor 3 has an open-circuit diameter of 60 mm and a short-circuit diameter of 90 mm. Within an axial distance of 48 mm to 653 mm from the open-circuit end, there is a circular arc-shaped periodic corrugated structure 2 with a depth of 3 mm, a width of 6 mm, and a spacing of 2 mm, and the surface is coated with a 5–10 nm thick TiN thin film.

[0043] During operation, the power source generates a 107.5MHz radio frequency signal, which is fed into the cavity via the input coupler 4 to establish a standing wave electromagnetic field. The resonant frequency is fine-tuned by the manual tuner 7 to precisely match the power source, thereby reducing reflected power and improving transmission efficiency. The periodic corrugated structure 2 on the surface of the inner conductor 3, in conjunction with the TiN thin film, effectively suppresses the secondary electron multiplication effect, improving the reliability and stability of the cavity operation. The focusing cavity further compresses the pulse width of the beam generated by the RF grid-controlled thermionic cathode electron gun of the petal accelerator, thereby improving the electron beam quality and significantly reducing beam loss.

[0044] By using a low-accelerating-voltage radio frequency cavity as the focusing cavity in a petal accelerator, the secondary electron multiplication effect can be effectively suppressed, significantly improving beam quality. The focusing cavity can compress the beam pulse width generated by the electron gun from the microsecond level to the nanosecond level, while simultaneously reducing beam emittance and energy dispersion, greatly reducing beam loss and improving the operational stability and reliability of the petal accelerator. Furthermore, this focusing cavity has a simple structure, is easy to fabricate, and has low cost, making it convenient for widespread application.

[0045] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details in the above embodiments. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention.

[0046] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not describe the various possible combinations separately.

[0047] Furthermore, various different implementations of the present invention can be combined arbitrarily, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed in the present invention.

Claims

1. A low accelerating voltage radio frequency cavity, comprising a standing wave resonant cavity, characterized in that, The inner conductor surface of the standing wave resonant cavity has a periodic corrugated structure with a circular arc cross section, and the inner conductor surface is coated with a TiN thin film with a thickness of 5-10 nm.

2. The low accelerating voltage radio frequency cavity according to claim 1, characterized in that, The standing wave resonant cavity is a quarter-wavelength resonant cavity composed of an inner and outer conductor coaxial structure.

3. The low accelerating voltage radio frequency cavity according to claim 2, characterized in that, The inner conductor has a tapered structure, and the diameter of the open-circuit end of the inner conductor is smaller than the diameter of the short-circuit end.

4. The low accelerating voltage radio frequency cavity according to claim 3, characterized in that, The periodic corrugated structure is disposed within a range of 48mm to 653mm axial distance from the open end of the inner conductor. The depth of the periodic corrugated structure is 1-5mm, the width is 4-8mm, and the spacing between adjacent corrugations is 1-3mm.

5. The low accelerating voltage radio frequency cavity according to claim 1, characterized in that, The TiN thin film was prepared using magnetron sputtering technology.

6. The low accelerating voltage radio frequency cavity according to claim 1, characterized in that, It also includes an input coupler, which is a ring-shaped magnetic coupling structure used to feed radio frequency power into the standing wave resonant cavity.

7. The low accelerating voltage radio frequency cavity according to claim 1, characterized in that, It also includes a radio frequency (RF) signal pickup unit, which is used to detect the amplitude and phase of the RF field within the standing wave resonant cavity.

8. The low accelerating voltage radio frequency cavity according to claim 1, characterized in that, It also includes a manual tuner for adjusting the resonant frequency of the radio frequency cavity.

9. The low accelerating voltage radio frequency cavity according to claim 1, characterized in that, The standing wave resonator also includes beam pipes that penetrate both ends of the standing wave resonator, and a vacuum pipe located outside the standing wave resonator and communicating with the inside of the standing wave resonator.

10. The low accelerating voltage radio frequency cavity according to claim 1, characterized in that, The low-acceleration voltage radio frequency cavity is used as the focusing cavity of the petal accelerator, and the resonant frequency of the focusing cavity is 107.5MHz.

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