Coaxial virtual cathode reflex triode array and method of modulating its radiation field

Abstract

The present application relates to coaxial reflection triode and its radiation field modulation method, specifically relates to a coaxial virtual cathode reflection triode array and its radiation field modulation method, the technical problems of the radiation field uniformity and irradiation area modulation difficulty of the coaxual virtual cathode reflection triode array output, and the lower radiation utilization rate are solved.The present application proposes according to the radiation distribution characteristics of single tube, the triodes in array are arranged into the form of concentric circle, through adjusting the radius of circle and the number of triodes, the spatial modulation of pulsed hard X-ray field can be realized, so as to obtain the radiation field of high energy flux and high uniformity;The characteristic that the radiation of triode single tube is stronger to the side front is used, the outer ring triode is inwardly inclined, the spatial modulation of radiation field is realized by controlling the inward inclination angle of the bottom of anode pedestal, so that the radiation field with large area is obtained, and the utilization rate of pulsed hard X-ray can also be improved.

Description

Technical Field

[0001] This invention relates to coaxial reflective transistors and modulation methods, specifically to a coaxial virtual cathode reflective transistor array and its radiation field modulation method. Background Technology

[0002] Pulsed hard X-rays with photon energies of 10 keV to 100 keV have important applications in the study of electromagnetic pulse effects. The fundamental method for obtaining pulsed hard X-rays is to bombard high-Z materials (materials with high atomic coefficients) with a high-current pulsed electron beam to generate bremsstrahlung. Currently, single-gap electron beam diodes are the main technology for generating pulsed hard X-rays. However, since generating pulsed hard X-rays requires electron energies below 300 keV, the efficiency of generating pulsed hard X-rays via bremsstrahlung is low, and the injection power density is limited by the electron energy. Therefore, the energy flux of pulsed hard X-rays cannot meet application requirements. Thus, it is necessary to develop new hard X-ray conversion loads to improve injection power density, energy conversion efficiency, and the utilization efficiency of pulsed hard X-rays.

[0003] In order to obtain higher energy flux pulsed hard X-rays, technicians have successively developed electron beam diode series-parallel technology, reflective transistor series-parallel technology, and coaxial virtual cathode reflective transistor series-parallel technology.

[0004] The thick target used in electron beam diodes absorbs low-energy rays severely, which greatly reduces the output of pulsed hard X-ray radiation; when a thin target is used, the remaining electron energy after the electron interacts with the target material once cannot be utilized, resulting in a decrease in the conversion efficiency of pulsed hard X-rays.

[0005] In a reflective transistor, electrons are reflected multiple times within the anode-cathode gap to strike the anode target, efficiently utilizing electron kinetic energy and improving the efficiency of electron-to-pulsed hard X-ray conversion. Based on their structure, reflective transistors can be divided into planar reflective transistors and coaxial reflective transistors. Coaxial reflective transistors offer higher pulsed hard X-ray conversion and utilization efficiencies, and structurally solve the series-parallel operation problem. However, they have two cathodes and one anode, resulting in a complex structure. Furthermore, the series voltage division requires precise adjustment of the anode-cathode gap, making control more difficult. In addition, the use of a single large-size coaxial anode target makes it difficult to effectively concentrate pulsed hard X-rays outside the anode target onto the irradiated area of ​​the effector, leading to lower pulsed hard X-ray utilization efficiency.

[0006] By removing the inner cathode from a coaxial reflective transistor, electrons passing through the anode target during operation form a virtual cathode inside the anode, giving it the characteristics of a coaxial reflective transistor. This significantly simplifies the structure, resulting in the coaxial virtual cathode reflective transistor. The series-parallel connection technique for coaxial virtual cathode reflective transistors utilizes a small-sized anode conversion target and arranges multiple transistors in an array according to a specific rule. This reduces the loss of pulsed hard X-rays outside the anode conversion target and increases the intensity of pulsed hard X-rays in the observation area. The overall impedance of the array can be adjusted through series and parallel connections, allowing for the use of large high-voltage pulse sources to further enhance the intensity of pulsed hard X-ray radiation.

[0007] The radiation field output by a coaxial virtual cathode reflector array in a detection plane can be viewed as a spatial superposition of multiple transistor radiation fields. If the transistors are densely arranged at the center of the array, a small-area radiation field with a strong center and a weak periphery will be generated; if the transistors are dispersed without a proper arrangement, it is difficult to generate a radiation field that simultaneously possesses a large area, high energy flux, and good uniformity. Therefore, a suitable radiation field modulation method is crucial for improving the quality of the radiation field. Summary of the Invention

[0008] The purpose of this invention is to solve the technical problems of uneven radiation field output and difficulty in modulating irradiation area and low radiation utilization rate of existing coaxial virtual cathode reflector transistor arrays, and to provide a coaxial virtual cathode reflector transistor array and its radiation field modulation method.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A coaxial virtual cathode reflective transistor array, comprising a grounded cathode, a grounded outer cylinder, an anode base, and an anode foil assembly, is characterized by:

[0011] The anode base is a cylindrical structure with one open end, and its open end is fixed to the output end face of the positive polarity pulse source. The bottom of the anode base includes an edge part, a connecting part and a central part that are coaxially arranged and connected in sequence from the outside to the inside. The edge part is a toroidal surface, the central part is a circular plane, and the connecting part is a conical surface with an inclination angle α, where 0° < α < 90°.

[0012] The grounding outer cylinder is coaxially mounted on the outside of the anode base, with its lower end fixed to the grounding end face of the positive polarity pulse source, and its upper end coaxially mounted with a grounding cathode. The grounding cathode is located above the bottom of the anode base, and the center of the grounding cathode has a downward recess, the shape of which is adapted to the bottom connection part and the center part of the anode base. The grounding cathode has cathode through holes that correspond one-to-one with the anode foils in the anode foil group. The lower end of the anode foil in the anode foil group is vertically fixed to the bottom of the anode base, and the upper end passes through the corresponding cathode through hole. Electrons accumulate inside the anode foil to form a virtual cathode, which, together with the corresponding cathode through hole, constitutes a coaxial virtual cathode reflector transistor.

[0013] The anode foils in the anode foil group are evenly distributed in three rings at the bottom of the anode base, and are referred to as the first ring, the second ring and the third ring from the inside out. The projections of the first ring, the second ring and the third ring on the grounding end face of the positive polarity pulse source are concentric circles, wherein the first ring is located in the central part, and the second ring and the third ring are located in the connecting part.

[0014] The number of anode foils arranged on the first, second, and third rings is proportional to their projection radius on the grounding terminal face of the positive polarity pulse source.

[0015] Furthermore, in order to generate a pulsed X-ray radiation field with a uniformity of 2:1 over a large detection area, the projection radii of the first ring, the second ring, and the third ring on the grounding end face of the positive polarity pulse source must satisfy the following condition:

[0016] 3.5R1 <R≤4R1

[0017] 2R1≤R2 <R3≤3R1

[0018] Where R1, R2, and R3 are the projection radii of the first ring, the second ring, and the third ring on the grounding end face of the positive polarity pulse source, respectively, and R is the radius of the irradiation area of ​​the coaxial virtual cathode reflector array.

[0019] Furthermore, the ratio of the number of anode foils arranged in the first ring to the sum of the number of anode foils arranged in the second and third rings is 1:4.5 to 1:5.5.

[0020] Furthermore, the inclination angle α at the bottom of the anode base ranges from 20° ≤ α ≤ 40°.

[0021] Furthermore, the operating environment of the grounded cathode, grounded outer cylinder, anode base, and anode foil is a vacuum degree of less than 1×10⁻⁶. -2 A vacuum environment of Pa.

[0022] This invention also provides a method for modulating the radiation field of a coaxial virtual cathode reflector array, used to modulate the radiation field of the aforementioned coaxial virtual cathode reflector array, characterized by comprising the following steps:

[0023] Step 1: Determine the required number of transistors N based on the impedance of a single coaxial virtual cathode reflector transistor and the total impedance of the coaxial virtual cathode reflector transistor array, i.e., the number of anode foils N in the anode foil group;

[0024] Step 2: Based on the irradiation area of ​​the coaxial virtual cathode reflective transistor array, determine the inclination angle α at the bottom of the anode base. Then, draw three concentric circles on the central part and connecting part of the bottom of the anode base, and label them as the first ring, the second ring and the third ring from the inside out. The first ring is located in the central part, and the second and third rings are located in the connecting part.

[0025] Step 3: Vertically fix the anode foil to the bottom of the anode base, so that the N anode foils in the anode foil group are evenly arranged on the first ring, the second ring and the third ring respectively;

[0026] Step 4: Coaxially mount the anode base and the grounding outer cylinder to the output end face and the grounding end face of the positive polarity pulse source, respectively. Then, coaxially mount the grounding cathode to the upper end of the grounding outer cylinder, so that the upper end of the anode foil passes through the corresponding cathode through hole on the grounding cathode, forming a coaxial virtual cathode reflective transistor array.

[0027] Step 5: Select the detection area within the irradiation area of ​​the set coaxial virtual cathode reflective transistor array;

[0028] Step 6: Measure the radiation field of the coaxial virtual cathode reflector array within the detection area selected in step 5. If the radiation field of the coaxial virtual cathode reflector array meets the set uniformity requirements, the modulation is completed. Otherwise, return to step 2 and adjust the projection radius of the first ring, the second ring, and the third ring on the grounding end face of the positive polarity pulse source, as well as the number of anode foils arranged on the first ring, the second ring, and the third ring.

[0029] Further, in step 1, the number of anode foils in the anode foil group is calculated using the following formula:

[0030] N = Z0 / Z t

[0031] Where Z0 is the impedance of the coaxial virtual cathode reflector transistor formed by the anode foil and its corresponding cathode via, Z t This represents the total impedance of the coaxial virtual cathode reflector array.

[0032] Compared with the prior art, the present invention has the following beneficial technical effects:

[0033] 1. The coaxial virtual cathode reflective transistor array proposed in this invention arranges the anode foil group in three rings evenly at the bottom of the anode base, thereby increasing the irradiation area of ​​the radiation field of the coaxial virtual cathode reflective transistor array; taking advantage of the strong radiation emitted by a single transistor to the side and front, the anode foil of the outer ring is tilted inward, thereby increasing the energy flux of the radiation field of the coaxial virtual cathode reflective transistor array; by controlling the number of anode foils on each ring, the uniformity of the radiation field of the coaxial virtual cathode reflective transistor array is enhanced.

[0034] 2. The radiation field modulation method of the coaxial virtual cathode reflective transistor array proposed in this invention is based on the radiation distribution characteristics of a single transistor. The transistors in the array are arranged in a concentric ring. By adjusting the radius of the ring and the number of transistors, spatial modulation of the pulsed hard X-ray field can be achieved, thereby obtaining a radiation field with a large area, high energy flux, and high uniformity. Taking advantage of the strong radiation emitted by a single transistor to the side and front, the outer ring transistors are tilted inward. By controlling the inward tilt angle of the bottom of the anode base, spatial modulation of the radiation field is achieved, while improving the utilization rate of the rays. Attached Figure Description

[0035] Figure 1 This is a cross-sectional view of an embodiment of the coaxial virtual cathode reflector array of the present invention;

[0036] Figure 2 This is a schematic diagram of the anode foil group arrangement in an embodiment of the coaxial virtual cathode reflective transistor array of the present invention;

[0037] Figure 3 This is a schematic diagram illustrating the working principle of the coaxial virtual cathode reflective transistor array of the present invention.

[0038] The annotations in the attached figures are explained as follows:

[0039] 1-Cathode through hole, 2-Anode foil, 3-Grounded cathode, 4-Grounded outer cylinder, 5-Anode base, 6-Detection area. Detailed Implementation

[0040] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a further detailed explanation of the coaxial virtual cathode reflective transistor array and its radiation field modulation method proposed in this invention. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of this invention and are not intended to limit the scope of protection of this invention.

[0041] A coaxial virtual cathode reflector array, such as Figure 1 As shown, it includes a grounded cathode 3, a grounded outer cylinder 4, an anode base 5, and an anode foil assembly. The grounded cathode 3, grounded outer cylinder 4, anode base 5, and anode foil assembly all operate at a vacuum level less than 1×10⁻⁶. - 2In a vacuum environment of Pa, the anode base 5 is a cylindrical structure with one open end, fixed to the output face of the positive polarity pulse source, and its bottom is inclined inward. The bottom of the anode base 5 includes an edge portion, a connecting portion, and a central portion arranged coaxially from the outside to the inside and connected in sequence. The edge portion is a toroidal surface, the central portion is a circular plane, and the connecting portion is a conical surface with an inclination angle α, where 20°≤α≤40°. The magnitude of the inclination angle α determines the irradiation area of ​​the coaxial virtual cathode reflector array radiation field and the utilization rate of pulsed hard X-rays. If the inclination angle α is too large, the irradiation area is small, but the utilization rate of pulsed hard X-rays is high.

[0042] The grounding outer cylinder 4 is coaxially mounted on the outside of the anode base 5, with its lower end fixed to the grounding end face of the positive polarity pulse source, and the grounding cathode 3 coaxially mounted on its upper end. The grounding cathode 3 is located above the bottom of the anode base 5, and has a downward recess in the middle, the shape of which matches the bottom connection part and the center part of the anode base 5. The grounding cathode 3 has cathode through holes 1 that correspond one-to-one with the anode foils 2 in the anode foil group. The anode foils 2 in the anode foil group are vertically mounted on the anode base 5, with their lower ends fixed to the bottom of the anode base 5 and their upper ends passing through the corresponding cathode through holes 1. Electrons accumulate inside the anode foil 2 to form a virtual cathode, which, together with its corresponding cathode through hole 1, constitutes a coaxial virtual cathode reflector transistor.

[0043] like Figure 2 As shown, the anode foils are arranged in three rings at the bottom of the anode base 5, and are designated as the first ring, second ring, and third ring from the inside out. The projections of the first ring, second ring, and third ring onto the grounding end face of the positive polarity pulse source are concentric circles, with the first ring located in the center and the second and third rings located at the connecting part to form a radiation converging structure. The number of anode foils 2 in the first, second, and third rings is proportional to their projection radius on the grounding end face of the positive polarity pulse source, ensuring that the axis of the anode foil 2 coincides with the circle and is perpendicular to the anode base 5. The anode foils 2 in each ring are evenly distributed, and the arrangement of the anode foils 2 cannot be too sparse, otherwise it will reduce the uniformity of the radiation field in the detection area directly opposite the ring; the arrangement of the anode foils 2 cannot be too dense either, otherwise it will reduce the utilization rate of pulsed hard X-rays. Overall, the anode foils 2 in the second and third rings are relatively close in spatial position and far from the first ring. If any ring of anode foil 2 is removed, the radiation field in a large-area observation area will exhibit an uneven distribution with high edges and low center. Therefore, the selection principles for the inward inclination angle α at the bottom of the anode base 5 and the number of anode foils 2 arranged in the first ring, second ring, and third ring are as follows:

[0044] Provided that the irradiation area and uniformity of the radiation field of the coaxial virtual cathode reflector array meet the set requirements, the utilization rate of pulsed hard X-rays should be as high as possible.

[0045] When the distance to the detection surface is the same, the radiation generated by the outer ring anode foil 2 will be lost outside the observation area more than that of the inner ring. Therefore, based on the characteristic that single-tube radiation emits stronger radiation to the side and front, the outer ring anode foil 2 is deflected towards the array center at a certain angle α to form a converging structure, such as... Figure 3 As shown, the central axes of the outer anode foil 2 intersect at a single point, which allows more radiation from the outer anode foil 2 to be projected into the observation area, further improving the radiation utilization rate and radiation field intensity.

[0046] The projected radii of the first, second, and third rings on the grounding terminal face of the positive polarity pulse source satisfy the following condition:

[0047] 3.5R1 <R≤4R1

[0048] 2R1≤R2 <R3≤3R1

[0049] Where R1, R2, and R3 are the projection radii of the first ring, the second ring, and the third ring on the grounding end face of the positive polarity pulse source, respectively, and R is the radius of the irradiation area of ​​the coaxial virtual cathode reflector array.

[0050] The ratio of the number of anode foils 2 arranged in the first ring to the sum of the number of anode foils 2 arranged in the second and third rings is 1:4.5 to 1:5.5, which can generate a pulsed X-ray radiation field with a uniformity of 2:1 over a large detection area. Here, uniformity refers to the ratio of the strongest to the weakest point of the radiation field.

[0051] This embodiment also provides a radiation field modulation method for the above-mentioned coaxial virtual cathode reflective transistor array, including the following steps:

[0052] Step 1: Determine the required number of transistors N based on the impedance of a single coaxial virtual cathode reflector transistor and the total impedance of the coaxial virtual cathode reflector transistor array, i.e., the number of anode foils 2 in the anode foil group is N.

[0053] The number N of anode foil 2 in the anode foil group is calculated using the following formula:

[0054] N = Z0 / Z t

[0055] Where Z0 is the impedance of the coaxial virtual cathode reflector transistor formed by the anode foil 2 and its corresponding cathode through-hole 1, Z t This represents the total impedance of the coaxial virtual cathode reflector array.

[0056] Step 2: Based on the irradiation area of ​​the coaxial virtual cathode reflective transistor array, determine the inward tilt angle α at the bottom of the anode base 5. Then, draw three concentric circles on the central part and the connecting part at the bottom of the anode base 5, and label them as the first ring, the second ring and the third ring from the inside out. The first ring is located in the central part, and the second and third rings are located in the connecting part.

[0057] Step 3: Vertically fix the anode foil 2 to the bottom of the anode base 5, so that the N anode foils 2 in the anode foil group are evenly arranged on three concentric circles;

[0058] Step 4: Coaxially mount the anode base 5 and the grounded outer cylinder 4 on the output end face and the grounding end face of the positive polarity pulse source, respectively. Then, coaxially mount the grounded cathode 3 on the upper end of the grounded outer cylinder 4, so that the upper end of the anode foil 2 passes through the corresponding cathode through hole 1 on the grounded cathode 3, forming a coaxial virtual cathode reflective transistor array.

[0059] Step 5: Select the detection area 6 within the irradiation area of ​​the set coaxial virtual cathode reflective transistor array;

[0060] Step 6: Measure the radiation field of the coaxial virtual cathode reflector array within the detection area 6 selected in step 5. If the radiation field of the coaxial virtual cathode reflector array meets the set uniformity requirements, the modulation is completed. Otherwise, return to step 2 and adjust the projection radius of the first ring, the second ring, and the third ring on the grounding end face of the positive polarity pulse source, as well as the number of anode foils 2 arranged on the first ring, the second ring, and the third ring.

[0061] The radiation field modulation method of the coaxial virtual cathode reflector array provided in this embodiment is simple, easy to implement, and flexible. It effectively reduces the loss of pulsed hard X-rays and improves the radiation utilization rate of pulsed hard X-rays. It can be used to generate pulsed hard X-rays with high energy flux, high uniformity, and large area.

Claims

1. A coaxial virtual cathode reflective transistor array, comprising a grounded cathode (3), a grounded outer cylinder (4), an anode base (5), and an anode foil assembly, characterized in that: The anode base (5) is a cylindrical structure with one end open. Its open end is fixed on the output end face of the positive polarity pulse source, and the bottom is inclined inward. The bottom of the anode base (5) includes an edge part, a connecting part and a central part that are coaxially arranged and connected in sequence from the outside to the inside. The edge part is a toroidal surface, the central part is a circular plane, and the connecting part is a conical surface with an inward inclination angle α, where 0° < α < 90°. The grounding outer cylinder (4) is coaxially installed on the outside of the anode base (5), with its lower end fixed to the grounding end face of the positive polarity pulse source and the grounding cathode (3) coaxially installed on its upper end; the grounding cathode (3) is located above the bottom of the anode base (5), and the grounding cathode (3) has a downward recess in the middle, and the shape of the recess is adapted to the bottom connection part and the center part of the anode base (5). The grounding cathode (3) has cathode through holes (1) that correspond one-to-one with the anode foils (2) in the anode foil group; the lower end of the anode foil (2) in the anode foil group is vertically fixed to the bottom of the anode base (5), and the upper end passes through the corresponding cathode through hole (1); electrons are gathered inside the anode foil (2) to form a virtual cathode, and it forms a coaxial virtual cathode reflector transistor with its corresponding cathode through hole (1); The anode foils (2) in the anode foil group are evenly distributed in three rings at the bottom of the anode base (5), and are referred to as the first ring, the second ring and the third ring from the inside out. The projections of the first ring, the second ring and the third ring on the grounding end face of the positive polarity pulse source are concentric circles, wherein the first ring is located in the central part, and the second ring and the third ring are located in the connecting part. The number of anode foils (2) arranged on the first ring, the second ring and the third ring is proportional to their projection radius on the grounding end face of the positive polarity pulse source.

2. The coaxial virtual cathode reflector array according to claim 1, characterized in that, The projected radii of the first ring, the second ring, and the third ring on the grounding terminal face of the positive polarity pulse source satisfy the following condition: 3.5R1 <R≤4R1 2R1≤R2 <R3≤3R1 Where R1, R2, and R3 are the projection radii of the first ring, the second ring, and the third ring on the grounding end face of the positive polarity pulse source, respectively, and R is the radius of the irradiation area of ​​the coaxial virtual cathode reflector array.

3. The coaxial virtual cathode reflector array according to claim 2, characterized in that: The ratio of the number of anode foils (2) arranged in the first ring to the sum of the number of anode foils (2) arranged in the second and third rings is 1:4.5 to 1:5.

5.

4. A coaxial virtual cathode reflector array according to claim 3, characterized in that: The inclination angle α at the bottom of the anode base (5) is in the range of 20°≤α≤40°.

5. A coaxial virtual cathode reflector array according to any one of claims 1-4, characterized in that: The working environment of the grounded cathode (3), grounded outer cylinder (4), anode base (5), and anode foil (2) is a vacuum degree less than 1×10⁻⁶. -2 A vacuum environment of Pa.

6. A method for modulating the radiation field of a coaxial virtual cathode reflector array as described in any one of claims 1-5, comprising the following steps: Step 1: Determine the required number of transistors N based on the impedance of a single coaxial virtual cathode reflector transistor and the total impedance of the coaxial virtual cathode reflector transistor array, i.e., the number N of anode foils (2) in the anode foil group; Step 2: Determine the inclination angle α at the bottom of the anode base (5) based on the irradiation area of ​​the coaxial virtual cathode reflective transistor array. Then, draw three concentric circles at the center and connecting parts of the bottom of the anode base (5), which are called the first ring, the second ring and the third ring from the inside out. The first ring is located in the center part, and the second and third rings are located in the connecting parts. Step 3: Vertically fix the anode foil (2) to the bottom of the anode base (5), so that the N anode foils (2) in the anode foil group are evenly arranged on the first ring, the second ring and the third ring respectively; Step 4: Install the anode base (5) and the grounded outer cylinder (4) coaxially on the output end face and grounding end face of the positive polarity pulse source, respectively. Then, install the grounded cathode (3) coaxially on the upper end of the grounded outer cylinder (4), so that the upper end of the anode foil (2) passes through the corresponding cathode through hole (1) on the grounded cathode (3) to form a coaxial virtual cathode reflective transistor array. Step 5: Select the detection area within the irradiation area of ​​the set coaxial virtual cathode reflective transistor array (6); Step 6: Measure the radiation field of the coaxial virtual cathode reflector array within the detection area (6) selected in step (5). If the radiation field of the coaxial virtual cathode reflector array meets the set uniformity requirements, the modulation is completed. Otherwise, return to step 2 and adjust the projection radius of the first ring, the second ring and the third ring on the grounding end face of the positive polarity pulse source, as well as the number of anode foils (2) arranged on the first ring, the second ring and the third ring.

7. The radiation field modulation method for a coaxial virtual cathode reflective transistor array according to claim 6, characterized in that: In step 1, the number of anode foils (2) in the anode foil group is calculated using the following formula: N = Z0 / Z t Where Z0 is the impedance of the coaxial virtual cathode reflector transistor formed by the anode foil (2) and its corresponding cathode through hole (1), Z t This represents the total impedance of the coaxial virtual cathode reflector array.

Images