Enhanced resonant cavity beam detector based on metamaterial

Abstract

The invention belongs to the technical field of particle radiotherapy, and particularly relates to a metamaterial-based enhanced resonant cavity beam detector, which comprises a reentrant resonant cavity, a metamaterial structure, a coupling receiving device and a beam pipeline, the reentrant resonant cavity comprises a resonant cavity outer conductor and a resonant cavity inner conductor; the resonant cavity inner conductor and the metamaterial are both located in the resonant cavity outer conductor; the beam pipeline comprises a first beam pipeline and a second beam pipeline; two ends of the resonant cavity outer conductor are respectively connected with a first beam pipeline and a second beam pipeline; and the coupling receiving device is connected with the resonant cavity outer conductor. The technical problems that an existing cavity type detector for low-repetition-frequency weak-flow particle beams is too large in size and low in sensitivity are solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of particle radiotherapy, and particularly relates to a resonant cavity type beam probe based on a metamaterial enhancement type, which is suitable for online detection of beam intensity of a proton therapy equipment based on a cyclotron. BACKGROUND

[0002] Proton therapy is an important technical means in the current precise radiotherapy field, and a proton radiotherapy equipment based on a cyclotron dominates the clinical application. However, the domestication process of the equipment still faces key technical challenges, especially in the aspect of beam monitoring: the existing beam monitoring technology cannot realize real-time online monitoring under the conditions of low repetition frequency and weak current (nA level), which restricts the further improvement of treatment safety and effectiveness. Traditional beam diagnosis equipment, such as a Faraday cup and a fluorescent target, belongs to an interception type probe, which can destroy the beam and cannot realize real-time monitoring; and a semi-interception type device (such as an ionization chamber) can partially realize real-time monitoring, but introduces beam divergence and energy loss, affecting the beam quality. Therefore, the development of a non-interception type, high-sensitivity beam probe has become one of the key requirements for the development of proton therapy technology. Existing non-interception type probes mainly include a beam transformer, a wall current probe and various cavity type beam monitors. The beam transformer is based on the electromagnetic induction principle, but its detection lower limit is usually microampere level, which cannot meet the measurement requirements of nanampere level weak beam; the wall current probe realizes measurement through the induction current on the inner wall of the beam pipeline, but the thermal noise is large, the signal-to-noise ratio is low, and it is difficult to work stably in a low current environment. The cavity type probe has become a potential solution for extremely weak beam monitoring due to its high sensitivity and narrow bandwidth characteristics.

[0003] Traditional cylindrical or rectangular cavity type beam probes measure beam intensity and position through TM010 mode and TM110 mode respectively, but have problems such as too large volume and low sensitivity in the application of low repetition frequency and weak current particle beam monitoring. Therefore, in view of the above problems, the present application develops a reentrant cavity probe based on a metamaterial unit, which has characteristics of high quality factor (Q value), small volume and anti-interference, and has important significance for realizing precise monitoring of proton therapy and other heavy ion low repetition frequency beams. SUMMARY

[0004] In view of the above defects or improvement requirements of the prior art, the present application provides a resonant cavity type beam probe based on a metamaterial enhancement type, which solves the technical problems of too large volume and low sensitivity of the existing cavity type probe for low repetition frequency and weak current particle beams.

[0005] To achieve the above object, according to one aspect of the present application, there is provided a reentrant cavity probe based on metamaterial, comprising a reentrant resonant cavity, a metamaterial, a coupling receiving device and a beam tube; the reentrant resonant cavity comprises an outer resonant cavity conductor and an inner resonant cavity conductor; the inner resonant cavity conductor and the metamaterial are located inside the outer resonant cavity conductor; The beam tube comprises a first beam tube and a second beam tube; the two ends of the outer resonant cavity conductor are connected to the first beam tube and the second beam tube respectively; the coupling receiving device is connected to the outer resonant cavity conductor.

[0006] Preferably, the metamaterial is specifically a complementary open split ring resonator; the complementary open split ring resonator comprises a metal outer ring, a metal inner ring and a plurality of metal bridges; the metal outer ring is connected to the outer resonant cavity conductor; each metal bridge connects the metal outer ring and the metal inner ring; a coupling line slot is formed between the metal outer ring and the metal inner ring; a first beam hole is arranged at the center of the metal inner ring.

[0007] Preferably, the inner resonant cavity conductor comprises a metal ring and an inner tube; a second beam hole is arranged at the center of the metal ring; one end of the inner tube is connected to the metal ring, and the inner tube and the center axis of the second beam hole are located on the same straight line.

[0008] Preferably, the center axes of the first beam tube, the second beam tube, the first beam hole and the second beam hole are located on the same straight line.

[0009] Preferably, the metal inner ring is located close to one end of the metal ring and is spaced apart from the metal ring.

[0010] Preferably, the coupling receiving device comprises a U-shaped coupling magnetic ring and a hollow cylindrical interface; one end of the U-shaped coupling magnetic ring is inserted into the hollow cylinder of the hollow cylindrical interface; the U-shaped coupling magnetic ring is located inside the outer resonant cavity conductor and in the region between the inner wall of the outer resonant cavity conductor and the outer wall of the inner tube, and the hollow cylindrical interface is located outside the outer resonant cavity conductor; a signal detection port is arranged on the side wall of the hollow cylindrical interface away from the U-shaped coupling magnetic ring.

[0011] Preferably, the reentrant cavity probe is provided with two coupling receiving devices, and the two coupling receiving devices are symmetric about the center of the inner tube.

[0012] Preferably, the materials of the outer resonant cavity conductor, the inner resonant cavity conductor, the metamaterial and the coupling receiving device are all oxygen-free copper.

[0013] Overall, compared with the prior art, the above technical scheme conceived by the present application can achieve the following beneficial effects: (1) The present application cooperatively designs the metamaterial and the reentrant resonant cavity, the core of which is that the metamaterial unit actively designs the electromagnetic field in the cavity, has an amplification effect on the electromagnetic field, and the signal voltage amplitude output by the detector is greatly increased for the same beam intensity. Moreover, under the condition of greatly reducing the physical size, the same low resonant frequency is still maintained. Ultimately, the detector realizes higher signal amplitude in a smaller volume, that is, the detection sensitivity is significantly improved.

[0014] (2) The metamaterial unit of the present application is a complementary split ring resonator, which realizes negative permittivity and negative permeability at the working frequency through subwavelength structure design, increases the equivalent permittivity to form a local field enhancement effect, balances the miniaturization and sensitivity demand by optimizing the number of coupling slot lines (double slot lines or multiple slot lines), and optimizes the electromagnetic field distribution through the periodic structure design of the metamaterial unit. The periodic structure design can suppress interference modes, and the axial electric field intensity of the TM010 mode is improved through the local field enhancement effect of the metamaterial unit.

[0015] (3) The coupling device of the present application is a magnetic coupling ring for outputting a voltage signal, two symmetrical coupling rings are arranged between the inner wall of the resonant cavity outer conductor and the outer wall of the inner tube, and the electromagnetic field signal in the cavity is extracted through magnetic coupling; the detector made of all-metal oxygen-free copper material avoids dielectric loss, improves the quality factor, and improves the thermal stability.

[0016] (4) The present application breaks through the technical limitation of non-intervention real-time monitoring of extremely weak beam by innovatively integrating the metamaterial and the reentrant cavity, and provides a high-performance diagnostic tool for precise radiotherapy and particle accelerator research. Research and numerical simulation show that the detector is significantly superior to existing technical solutions in terms of sensitivity, response speed and anti-interference performance. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a schematic view of the three-dimensional structure of the detector of the present application.

[0018] Figure 2 is a schematic view of the structure of the resonant cavity inner conductor of the present application.

[0019] Figure 3 is an electromagnetic field simulation diagram of the detector of the present application.

[0020] Figure 4 is a structure diagram of the metamaterial unit of the present application.

[0021] Figure 5 is a structure diagram of the ring coupler of the present application.

[0022] In all the drawings, the same reference signs are used to represent the same elements or structures, wherein: 1, resonant cavity outer conductor; 2, resonant cavity inner conductor; 3, metamaterial; 4, coupling receiving device; 5, beam pipe; 21 metal ring; 22, inner tube; 23, second beam hole; 31 metal outer ring; 32 coupling line slot; 33 metal inner ring; 34 first beam hole; 35 metal bridge; 41, U-shaped coupling magnetic ring; 42, hollow cylindrical interface; 43, signal detection port; 51, first beam pipe; 52, second beam pipe. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0024] Example 1 Figure 1 is a sectional view of the present application for beam intensity probe, which intuitively shows the structure inside the cavity, including resonant cavity outer conductor 1, resonant cavity inner conductor 2, metamaterial 3, coupling receiving device 4, beam pipe 5. The beam pipe 5 includes first beam pipe 51 and second beam pipe 52, and the two ends of the resonant cavity outer conductor 1 are connected with the first beam pipe 51 and the second beam pipe 52 respectively.

[0025] Figure 2 is a structural schematic diagram of the resonant cavity inner conductor 2 of the present application, and the resonant cavity inner conductor 2 includes a metal ring 21 and an inner tube 22; the center of the metal ring 21 is provided with a second beam hole 23; one end of the inner tube 22 is connected with the metal ring 21, and the center axis of the inner tube 22 and the second beam passage 23 is located on the same straight line.

[0026] Figure 4It is the schematic diagram of the super-structured material structure adopted by the present application. A complementary split ring resonator (CeSRR) is adopted, which comprises a metal outer ring 31, a metal inner ring 33, and a plurality of metal bridges 35. The metal outer ring 31 is connected with the resonant cavity outer conductor 1. Each metal bridge 35 connects the metal outer ring 31 and the metal inner ring 33. A coupling line slot 32 is formed between the metal outer ring 31 and the metal inner ring 33. A first beam hole 34 is arranged at the center of the metal inner ring 33. The central axes of the first beam pipe 51, the second beam pipe 52, the first beam hole 34 and the second beam hole 23 are located on the same straight line. The metal inner ring 33 is located close to one end of the metal ring 21 and is spaced apart from the metal ring 21. The central metal inner ring 33 provides a particle injection channel, and the entire unit structure has electromagnetic resonance characteristics. The super-structured material is embedded in the center position of the reentrant cavity capacitance area. The working frequency band of the super-structured material should match the resonant frequency of the cavity. The function of the super-structured material is to construct a negative refractive index passband, so as to realize the transmission of electromagnetic waves below the cutoff frequency of the resonant cavity. The electromagnetic characteristics of the super-structured material are independent of the inherent properties of the material used for production, but depend on its shape, size and arrangement of units. Therefore, the appropriate size parameters of the super-structured material need to be designed according to the expected index parameters of the reentrant cavity detector (cavity expected working frequency, cavity size, etc.). Then, the S parameter solving method is used to verify whether the structure can provide a negative refractive index passband that meets the working frequency of the detector, that is, a transmission passband with both equivalent permittivity and equivalent permeability being negative.

[0027] Figure 5The coupling receiving device used in the application is the coupling receiving device 4, which comprises a U-shaped coupling magnetic ring 41 and a hollow cylindrical interface 42; one end of the U-shaped coupling magnetic ring 41 is inserted into the hollow cylinder of the hollow cylindrical interface 42; the U-shaped coupling magnetic ring 41 is located inside the resonant cavity outer conductor 1 and in the area between the inner wall of the resonant cavity outer conductor 1 and the outer wall of the inner tube 22, and the hollow cylindrical interface 42 is located outside the resonant cavity outer conductor 1; the side wall of the hollow cylindrical interface 42 is provided with a signal detection port 43 away from the U-shaped coupling magnetic ring 41. The reentrant cavity probe is provided with two coupling receiving devices 4, which are symmetric about the center of the inner tube 22. The coupling receiving device 4 is used to extract the output signal of the cavity probe. According to Faraday's law of electromagnetic induction, a changing magnetic field induces an electromotive force in the magnetic coupling ring 41, which is connected to the electronic system through a coaxial line. The coupling ring is equivalent to a high-frequency current source, and its output impedance needs to be matched with the subsequent circuit. The standard impedance of the hollow cylindrical interface 42 is 50Ω, which is matched with the input impedance of the subsequent signal processing device to avoid signal reflection. The signal detection port 43 is followed by a phase-locked amplifier as a signal processing device. It can extract the signal of a specified frequency band centered on the reference frequency and filter out all other frequency components outside the specified frequency band, especially for the output signal of the cavity probe working in the multi-beam mode, which can achieve ideal sensitivity.

[0028] The resonant cavity inner conductor 2 has a chamfer at the edge and the link to reduce the maximum electric field strength in the cavity, reduce the field strength fluctuation, and suppress the cavity high-order mode. In engineering, the design of the chamfer is also convenient for processing. The coupling receiving device 4 is a device for extracting the electromagnetic field signal in the cavity, the coupling ring plane normal is orthogonal to the cavity radius direction, and the output is a voltage signal. The beam pipe 5 is used to connect the cavity to the beam transport line.

[0029] The resonant cavity outer conductor 1, the resonant cavity inner conductor 2, the metamaterial 3 and the coupling receiving device 4 are all made of oxygen-free copper. Oxygen-free copper has high conductivity, and the surface impedance of the resonant cavity inner wall made of oxygen-free copper is smaller. In order to obtain a higher amplitude output signal of the cavity probe in the multi-beam mode under the condition of weak proton beam, selecting oxygen-free copper as the processing material can better slow down the attenuation of the electromagnetic field signal in the cavity, and then superimpose a stronger induced voltage in the cavity.

[0030] Figure 3It is the electromagnetic field simulation diagram of the beam intensity probe of the application, which can more intuitively illustrate the application. The left diagram is the electric field simulation diagram of the beam intensity probe of the application, and the right diagram is the magnetic field simulation diagram of the beam intensity probe of the application. The corresponding working mode in the diagram is quasi-TM010 mode. The electric field energy is concentrated in the capacitive region, and the magnetic field energy is concentrated in the coaxial region. The coaxial region is composed of the beam pipeline extending to the inner wall of the cavity, and the capacitive region is composed of the end metal disc and the metamaterial. The longitudinal electric field is stronger near the side of the CeSRR unit, which is due to the strong resonance characteristics of the CeSRR unit near the slot line, which makes the longitudinal electric field deviate to the side of the CeSRR unit. The electric field intensity in the center of the axis changes little, and when the beam has a slight displacement in the x direction or y direction on the axis, it will not bring great error.

[0031] The simulation test is carried out on the proton beam with a beam bunch repetition frequency of 73MHz and a beam intensity of 0.35nA. The TM010 mode frequency of the designed detection cavity is 4 times (292MHz) of the beam bunch repetition frequency, the radius of the cavity is only 8.5cm, and the total length of the cavity is 14.6cm. The cavity response time is about 20μs, the output voltage amplitude of the coupler can reach 20nV, and the sensitivity is as high as 57nV / nA.

[0032] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the application, and is not intended to limit the application. Any modification, equivalent replacement and improvement made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A re-entrant cavity detector based on metamaterials, characterized in that, It comprises a reentrant resonant cavity, a superstructure material (3), a coupling receiving device (4) and a beam pipe (5); the reentrant resonant cavity comprises a resonant cavity outer conductor (1) and a resonant cavity inner conductor (2); the resonant cavity inner conductor (2) and the superstructure material (3) are located inside the resonant cavity outer conductor (1). The beam pipe (5) comprises a first beam pipe (51) and a second beam pipe (52); the two ends of the resonant cavity outer conductor (1) are connected with the first beam pipe (51) and the second beam pipe (52) respectively; the coupling receiving device (4) is connected with the resonant cavity outer conductor (1).

2. A re-entrant cavity probe based on metamaterials as defined in claim 1, wherein, The superstructure material (3) is specifically a complementary open loop resonator; the complementary open loop resonator comprises a metal outer ring (31), a metal inner ring (33) and a plurality of metal bridges (35); the metal outer ring (31) is connected with the resonant cavity outer conductor (1); each metal bridge (35) connects the metal outer ring (31) and the metal inner ring (33); a coupling line slot (32) is formed between the metal outer ring (31) and the metal inner ring (33); a first beam hole (34) is arranged at the center of the metal inner ring (33).

3. A re-entrant cavity probe based on metamaterials as defined in claim 2, wherein, The resonant cavity inner conductor (2) comprises a metal ring (21) and an inner tube (22); a second beam hole (23) is arranged at the center of the metal ring (21); one end of the inner tube (22) is connected with the metal ring (21), and the center axis of the inner tube (22) and the second beam hole (23) are located on the same straight line.

4. A re-entrant cavity probe based on metamaterials as claimed in claim 3, wherein, The center axes of the first beam pipe (51), the second beam pipe (52), the first beam hole (34) and the second beam hole (23) are located on the same straight line.

5. A re-entrant cavity probe based on metamaterials as defined in claim 4, wherein, The metal inner ring (33) is located close to one end of the metal ring (21) and is spaced apart from the metal ring (21).

6. A re-entrant cavity probe based on metamaterials as defined in claim 5, wherein, The coupling receiving device (4) comprises a U-shaped coupling magnetic ring (41) and a hollow cylindrical interface (42); one end of the U-shaped coupling magnetic ring (41) is inserted into the hollow cylinder of the hollow cylindrical interface (42); the U-shaped coupling magnetic ring (41) is located inside the resonant cavity outer conductor (1) and in the region between the inner wall of the resonant cavity outer conductor (1) and the outer wall of the inner tube (22), and the hollow cylindrical interface (42) is located outside the resonant cavity outer conductor (1); the side wall of the hollow cylindrical interface (42) is away from the U-shaped coupling magnetic ring (41) and is provided with a signal detection port (43).

7. A re-entrant cavity probe based on metamaterials as defined in claim 6, wherein, The reentrant cavity probe is provided with two coupling receiving devices (4), and the two coupling receiving devices (4) are symmetric about the center of the inner tube (22).

8. A re-entrant cavity probe based on metamaterials as defined in claim 1, wherein, The materials of the resonant cavity outer conductor (1), the resonant cavity inner conductor (2), the superstructure material (3) and the coupling receiving device (4) are all oxygen-free copper.

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