Quantitative electron beam axis combination system for X-ray imaging

Abstract

The invention discloses a quantitative electron beam axis combination system for X-ray imaging, and relates to the technical field of transmission electron microscope atomic scale in-situ mechanics. Comprising an anode, a first coil, a second coil, a fourth connecting piece, a flange and a shell, the flange and the fourth connecting piece are each of an axisymmetric structure, the flange is fixedly connected to the shell, the fourth connecting piece is arranged in the flange, the first coil is wound around the top of the fourth connecting piece, and the second coil is wound around the bottom of the fourth connecting piece; the first coil and the second coil are electrically connected with an external power source, a fourth electron channel is arranged in the center of the fourth connecting piece, and electron beams emitted by the electron gun complete axis combination under the action of the first coil and the second coil when passing through the fourth electron channel. In the electron beam excitation process, different axis combination types and axis combination angles can be corrected, and the relation between the coil current size and coil configuration and the excitation magnetic field size and the relation between the deflection angle and the coil current size during axis combination are fundamentally established.

Description

Technical Field

[0001] The present invention belongs to the technical field of atomic scale in-situ mechanics of transmission electron microscopes, and more specifically, relates to a quantitative electron beam alignment system for X-ray imaging. Background Art

[0002] An X-ray tube is a device that can generate X-rays. Its working principle is to use high-speed electrons to hit a metal target surface to generate X-rays. X-ray tubes usually contain two electrodes: a cathode and an anode, which are sealed in a high vacuum glass or ceramic shell. The cathode emits electrons by heating, while the anode receives electron bombardment, thereby generating X-rays.

[0003] X-ray tubes are the most practical X-ray generating devices and have been widely used in X-ray instruments. X-ray tubes are used for diagnosis and treatment in medicine, and for non-destructive testing of materials, structural analysis, spectral analysis, and film exposure in industrial technology.

[0004] With the wide application in the above fields, how to develop X-ray tubes with small focus, fast deflection and good stability has become a hot research topic. Usually, the electron beam emitted from the cathode is divergent and tilted. The cause is the misalignment of the mechanical structure and the small vibration displacement between the filament and the grid. After the electron gun is fired, the displacement scale is magnified to form a non-negligible tilt error. Therefore, a deflection coil is often required at the rear end of the electron gun to realize the axis co-ordination function, so that the entire electron beam can be centered and then focused.

[0005] Research on deflection coils is often limited to large-scale macroscopic deflection, but there is a lack of research and design in the field of microscopic precision deflection coils. Therefore, it is particularly important to design a deflection coil axis system. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a quantitative electron beam alignment system for X-ray imaging, which can quantitatively correct the deflection angle, correct different alignment types and alignment angles during the electron beam excitation process, and fundamentally establish the relationship between the coil current size and coil configuration and the excitation magnetic field size, and the relationship between the deflection angle and the coil current size during alignment.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: a quantitative electron beam alignment system for X-ray imaging, including an anode, a first coil, a second coil, a fourth connecting piece, a flange, and a shell. The flange and the fourth connecting piece are both axisymmetric structures. The flange is upright and fixedly connected to the shell. The fourth connecting piece is upright arranged in a cavity inside the flange. The first coil is wound around the top of the fourth connecting piece, and the second coil is wound around the bottom of the fourth connecting piece. The first coil and the second coil are both electrically connected to an external power supply. The space between the fourth connecting piece and the flange is vacuum. A fourth electron channel is provided at the center of the fourth connecting piece. When the electron beam emitted by the electron gun passes through the fourth electron channel, the alignment is completed under the action of the first coil and the second coil.

[0008] Preferably, the flange includes an upper flange and a lower flange, the bottom end surface of the upper flange is provided with a circle of positioning bosses, the upper end surface of the lower flange is provided with a groove, the positioning bosses are embedded in the groove to first position the upper flange and the lower flange, and then the upper flange and the lower flange are welded and connected to form a whole.

[0009] Preferably, a positioning hole is provided at the bottom of the lower flange, the bottom end of the fourth connecting member is embedded in the positioning hole to position the fourth connecting member, the bottom end of the fourth connecting member is welded to the lower flange, and the top end of the fourth connecting member is welded to the upper flange.

[0010] Preferably, a third electron channel is provided on the top of the upper flange, and the third electron channel is connected to the fourth electron channel.

[0011] Preferably, an external thread is provided at the top of the upper flange, the anode is threadedly connected to the upper flange, a second electron channel is provided at the center of the anode, and the second electron channel is connected to the third electron channel.

[0012] Preferably, a third wire channel is provided at the bottom of the lower flange, a first wire channel and a second wire channel are provided on the outer shell, two ends of the second wire channel are respectively connected to the third wire channel and the first wire channel, and the wires pass through the first wire channel, the second wire channel, and the third wire channel in sequence from the outside of the outer shell into the cavity of the flange to electrically connect the first coil and the second coil.

[0013] Preferably, the axis of the second wire channel is parallel to the axis of the housing, and a sealing groove is provided around the second wire channel. An O-ring is installed in the sealing groove, and the O-ring seals the junction between the second wire channel and the third wire channel 111.

[0014] Preferably, the fourth connecting member is made of pure iron.

[0015] The beneficial effects of adopting the above technical solution are:

[0016] 1. The present invention adopts the first coil and the second coil to quantitatively correct the deflection angle, corrects different types of axis alignment and axis alignment angles during the electron beam excitation process, realizes the tilt axis alignment and translation axis alignment of the electron beam, and fundamentally establishes the relationship between the coil current size and the coil configuration and the excitation magnetic field size, and the relationship between the deflection angle and the coil current size during axis alignment.

[0017] 2. In the present invention, both the flange and the fourth connecting member adopt an axisymmetric structure, which can ensure the structural stability of the quantitative electron beam axis combination system and reduce the influence of electromagnetic noise on system performance.

[0018] 3. The first coil and the second coil are in a vacuum state, so that the process of external power transmission to the coils is separated from the movement of high-energy electrons, thereby preventing the entire system from leaking vacuum and reducing the quality of electron beam imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic cross-sectional view of the overall structure of the present invention;

[0020] Figure 2 It is a schematic diagram of the cross-sectional structure of the flange;

[0021] Figure 3 It is a schematic diagram of the cross-sectional structure of the shell;

[0022] In the figure: 1. electron gun; 2. shell; 21. first electron channel; 22. first wire channel; 23. second wire channel; 24. sealing groove; 3. first connecting piece; 4. second connecting piece; 5. third connecting piece; 6. target material; 7. anode; 71. second electron channel; 8. first coil; 9. upper flange; 91. third electron channel; 10. fourth connecting piece; 101. fourth electron channel; 11. lower flange; 111. third wire channel; 12. second coil. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0024] Specifically, Figure 1-2As shown, the electron beam alignment system includes an anode 7, a first coil 8, a second coil 12, a fourth connecting member 10, an upper flange 9, a lower flange 11, and a housing 2. The bottom end surface of the upper flange 9 is provided with a circle of positioning bosses, and the upper end surface of the lower flange 11 is provided with a groove. The positioning bosses are embedded in the groove to first position the upper flange 9 and the lower flange 11, and then the upper flange 9 and the lower flange 11 are connected by laser welding to form a whole. The top of the upper flange 9 is provided with an external thread, and the anode 7 is threadedly connected to the upper flange 9. A second electron channel 71 is provided at the center of the anode 7, a fourth electron channel 101 is provided at the center of the fourth connecting member 10, and a third electron channel 91 is provided at the top of the upper flange 9. The second electron channel 71 is connected to the third electron channel 91, and the third electron channel 91 is connected to the fourth electron channel 101. The electron beam emitted by the electron gun 1 passes through the second electron channel 71, the third electron channel 91, and the fourth electron channel 101 in sequence. When passing through the fourth electron channel 101, the electron beam is aligned with the first coil 8 and the second coil 12 and then projected onto the target 6 to generate X-rays. The first connector 3, the second connector 4 and the third connector 5 are all structural connectors of the X-ray generator.

[0025] A positioning hole is provided at the bottom of the lower flange 11, and the bottom end of the fourth connecting member 10 is embedded in the positioning hole to position the fourth connecting member 10 and play a certain sealing role. The bottom end of the fourth connecting member 10 is connected to the lower flange 11 by laser welding. The space between the fourth connecting member 10 and the upper and lower flanges is a sealed vacuum space. The first coil 8 is wound on the top of the fourth connecting member 10, and the second coil 12 is wound on the bottom of the fourth connecting member. The first coil 8 and the second coil 12 are both electrically connected to an external power source through wires. Figure 2 As shown, a third wire channel 111 is provided at the bottom of the lower flange 11. Figure 3 As shown, a first wire channel 22 and a second wire channel 23 are provided on the housing 2, and the two ends of the second wire channel 23 are respectively connected to the third wire channel 111 and the first wire channel 22. A sealing groove is provided around the second wire channel 23, and an O-ring is installed in the sealing groove, and the O-ring seals the connection between the second wire channel 23 and the third wire channel 111. The wires pass through the first wire channel 22, the second wire channel 23, and the third wire channel 111 from the outside of the housing 2 in sequence and enter the cavity of the upper and lower flanges to electrically connect the first coil 8 and the second coil 12.

[0026] Specifically, the first coil 8 and the second coil 12 can be selected as an annular deflection coil. Compared with other common saddle-shaped or multi-pole shoe coils, the annular deflection coil requires a larger current to excite the same magnetic field, but generates less inductance and occupies a smaller volume, and can achieve a uniform magnetic field of 10% in the central area. The uniformity of the magnetic field is directly related to the spherical aberration of the system, so the size of the uniform deflection area is directly related to the axis-matching range, which is not specifically limited in the embodiment of the present invention.

[0027] In the present invention, the fourth connecting member 10 is equivalent to the magnetic core of the first coil 8 and the second coil 12, and the fourth connecting member 10 is made of pure iron. The magnetic core of the first coil 8 and the second coil 12 is selected to use an iron core, because the iron core is hard and not easy to be damaged during the coil winding process, and the other ferrites are generally brittle and not suitable. After calculating that the magnetization strength of the iron core is sufficient and the cost is low, the fourth connecting member 10 is made of pure iron. In addition, the surface of the fourth connecting member 10 needs to be galvanized or sprayed to prevent oxidation.

[0028] The first coil 8 and the second coil 12 are wound by a winding machine and are produced by Suzhou Xiepu Winding Factory. Wind 40 turns on each winding, and mark on the fourth connecting piece 10 to ensure that each winding is vertical to ensure that the electron beam is deflected in two perpendicular directions. The winding can be evenly wound, and a magnetic field test survey can be done later to ensure that the magnetic field strength is uniform within the 3mm area of ​​the center area. After winding, glue needs to be used to fix the coil, because the wire is relatively thin and easily affected by external forces, and the enameled wire paint is relatively thin and is not suitable for heating and baking to solidify. The effect of using organic solvents to solidify the wire is too thin, so glue is used to fix it. The reason why the upper and lower flanges are laser welded is that the temperature of laser welding is relatively low, and the temperature of the paint skin of the enameled wire generally starts to melt at more than 200 degrees, and melts instantly at more than 400 degrees. The hot welding temperature is too high, so laser welding can only be selected.

[0029] In an optional embodiment of the present invention, the quantitative electron beam axis alignment system can uniformly design flanges, uniformly process the magnetic coil core, i.e., the fourth connector 10, uniformly process the flanges used for packaging, and uniformly process the winding production and assembly, so as to achieve mass production and improve the consistency and yield of the products. However, the coil still needs to be energized for testing, because errors will occur in the processing process, the coil winding process, and the solid fixation of the coil. Therefore, although mass production is possible, the uniformity of the magnetic field needs to be tested in the end.

[0030] Specifically, the quantitative electron beam alignment system deflection coil processing method can be carried out according to the following steps:

[0031] Step 1: Determine the beam spot width of the electron source electron beam, determine the required uniform magnetic field width, and select the approximate coil size. 10 times the required magnetic field width is roughly the size of the magnetic core.

[0032] Step 2: Design and process the coil core, i.e., the fourth connecting piece 10. Among them, the cores of the first coil 8 and the second coil 12 are slightly different. The inner diameter of the core of the first coil 8 is 8-12mm, the length is 6-10mm, and the width is 2-4mm; the inner diameter of the core of the second coil 12 is 8-10mm, the length is 4-6m, and the width is 4-6mm. The principle is that when the first coil 8 and the second coil 12 are the same when deflected at the same angle, the current magnitudes of the two coils are in a certain proportion. If the configuration of the coil is modified at the beginning, the same current can be used to achieve a co-axial task. The ratio here is determined by the distance from the electron source to the coil and the distance between the two coils. The specific formula will not be repeated here, and the coil core is not quantified, depending on specific needs.

[0033] Step 3: After determining the coil, design the flange, and use the national standard vacuum flange to connect the bottom to ensure that the coil can be encapsulated.

[0034] Step 4: Wind the coil. When winding the coil, make sure the winding is neat and tidy, without any intersecting wires. And glue the wound coil in time to keep the upper and lower centers of the coil in the same horizontal plane.

[0035] Step 5: Install the deflection coil, install the wound coil at the predetermined position inside the flange, lead out the wire, and mark it for the convenience of subsequent power transmission to the coil. The flange is then sealed by laser welding.

[0036] Step 6: Use a power source to transmit electricity to the coil. When transmitting electricity, distinguish the in and out of the coil according to the markings on the copper wire ends of the coil.

[0037] The anode 7 is grounded and its voltage is zero. It accelerates the high-energy electron beam and is often designed at the upper end of the coaxial coil in mechanical design. The specific anode design is not mentioned here. This article designs a threaded connection with it.

[0038] The electron gun 1 provides the entire X-ray system with an accelerated high-energy electron beam, which has two types: thermal emission and field emission. The basic structure consists of a filament, a grid, and an electrode. The relative slight displacement of the filament and the grid will cause the electron beam to tilt and deviate, which is the main reason for the tilted axis. For the specific electron gun design, please refer to other patent designs, which are not limited in this article.

[0039] The upper and lower flanges serve to isolate the atmosphere from the inside of the system and to supply power to the coil system. The connections are designed according to national standards to ensure vacuum, and the cavity size can be modified according to national standards.

[0040] The present invention adopts a first coil 8 and a second coil 12 to form a double deflection coil configuration. The double deflection coil configuration can achieve the tasks of tilting and translating the electron beam, which cannot be achieved by a single coil.

[0041] Specifically, the input current and the excited magnetic field of the toroidal coil with iron shield are as follows,

[0042] B is the magnetic field excited by the coil, N is the number of turns, I is the current, and K is the shape factor of the coil. The calculation formula is as follows:

[0043]

[0044] N0 is the total number of turns of the single-side winding of the coil. n(α) is the winding function distribution of the coil.

[0045] From the above formula, it can be obtained that the shape factor of the 0-90 degree toroidal coil is 0.9.

[0046] The axis-coupling function of the axis-coupling coil needs to satisfy the functions of translation axis-coupling and tilt axis-coupling. Translation offset is mainly caused by the error of the mechanical structure, which leads to the translation offset of the entire electron beam; tilt offset is mainly caused by a small displacement between the filament and the grid of the electron source part. This displacement is magnified by the distance in the spatial scale, and a small displacement will produce a large deflection, such as the vibration of the filament.

[0047] To implement the axis-joining function, follow these steps:

[0048] The first step is to determine the angle of the translation and tilt coil required for the axis alignment.

[0049] The second step is to infer the required magnetic field through the coil and angle.

[0050] The third step is to obtain the current of the coil from the magnetic field to realize the entire axis-coupling process.

[0051] The deflection angle in the magnetic field is linearly related to the magnetic field strength in the paraxial case, so the deflection angle should also be in the paraxial case during the axis coordinating program. Otherwise, the relationship between the two will have nonlinear high-order quantities, which is very complicated for current input. Therefore, the axis coordinating design should try to consider the paraxial case.

[0052] The specific formula is:

[0053] θ is the required deflection angle, m and q are the electron mass and charge, Ea is the relativistically corrected acceleration voltage, and H is the magnetic field thickness (for example, for the example given in this article, the uniform area is about 3 mm, which meets the requirements of the magnetic field on the co-axis. For other designs, separate calculation simulations are required).

[0054] The combined axis of translational deflection is affected by the following parameters: δ is the translational displacement of the electron beam, L2 is the distance between the first deflection magnetic field and the second deflection magnetic field, α is the deflection angle in the deflection coil. At this time, the deflection angles in the first and second coils 12 are the same: α = δ / L2.

[0055] The electron beam is displaced by two identical deflection angles without any angular deflection.

[0056] The combined axis of the tilt deflection is affected by the following parameters: L1 is the distance between the grid and the first deflection magnetic field, L2 is the distance between the first deflection magnetic field and the second deflection magnetic field, α is the tilt deflection angle, and α1 and α2 are the deflection angles in the first magnetic field and the second magnetic field. When α is determined, the deflection path and the deflection angle are determined. α·L1 / L2=α2, α1=α·(L1 / L2+1), α1=α+α2. It can be seen that when the α deflection angle changes linearly, α1 and α2 also change linearly.

[0057] In summary, in the cases of translation and tilt axis matching, the current of the coil changes linearly. The correction of tilt axis matching and translation axis matching in a single direction can be completed according to the above formula. The conventional coil has four windings, two of which complete the correction in one direction. The four groups cooperate to complete the axis matching in mutually perpendicular directions according to the above formula. The two layers of coils jointly complete the axis matching in the case of translation and tilt, thereby realizing the axis matching operation.

[0058] The above are only preferred specific implementation modes of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A quantitative electron beam alignment system for X-ray imaging, characterized in that: The invention comprises an anode (7), a first coil (8), a second coil (12), a fourth connecting piece (10), a flange, and a housing (2). The flange and the fourth connecting piece are both axially symmetrical structures. The flange is vertically fixedly connected to the housing (2). The fourth connecting piece (10) is vertically arranged in a cavity inside the flange. The first coil (8) is wound around the top of the fourth connecting piece (10). The second coil (12) is wound around the bottom of the fourth connecting piece. The first coil (8) and the second coil (12) are both electrically connected to an external power supply. The space between the fourth connecting piece (10) and the flange is vacuum. A fourth electron channel (101) is arranged at the center of the fourth connecting piece (10). When an electron beam emitted by an electron gun (1) passes through the fourth electron channel (101), the electron beam is aligned under the action of the first coil (8) and the second coil (12).

2. A quantitative electron beam alignment system for X-ray imaging according to claim 1, characterized in that: The flange comprises an upper flange (9) and a lower flange (11). The bottom end surface of the upper flange (9) is provided with a circle of positioning bosses, and the upper end surface of the lower flange (11) is provided with a groove. The positioning bosses are embedded in the groove to first position the upper flange (9) and the lower flange (11), and then the upper flange (9) and the lower flange (11) are welded and connected to form a whole.

3. A quantitative electron beam alignment system for X-ray imaging according to claim 2, characterized in that: A positioning hole is provided at the bottom of the lower flange (11), and the bottom end of the fourth connecting member (10) is embedded in the positioning hole to position the fourth connecting member (10). The bottom end of the fourth connecting member (10) is welded to the lower flange (11), and the top end of the fourth connecting member (10) is welded to the upper flange (9).

4. The quantitative electron beam alignment system for X-ray imaging according to claim 2, characterized in that: A third electron channel (91) is provided on the top of the upper flange (9), and the third electron channel (91) is connected to the fourth electron channel (101).

5. The quantitative electron beam alignment system for X-ray imaging according to claim 4, characterized in that: The top of the upper flange (9) is provided with an external thread, the anode (7) is threadedly connected to the upper flange (9), a second electron channel (71) is provided at the center of the anode (7), and the second electron channel (71) is connected to a third electron channel (91).

6. The quantitative electron beam alignment system for X-ray imaging according to claim 2, characterized in that: A third wire channel (111) is provided at the bottom of the lower flange (11), a first wire channel (22) and a second wire channel (23) are provided on the outer shell (2), two ends of the second wire channel (23) are respectively connected to the third wire channel (111) and the first wire channel (22), and wires pass through the first wire channel (22), the second wire channel (23), and the third wire channel (111) from the outside of the outer shell (2) in sequence and enter the cavity of the flange to electrically connect the first coil (8) and the second coil (12).

7. A quantitative electron beam alignment system for X-ray imaging according to claim 6, characterized in that: The axis of the second wire channel (23) is parallel to the axis of the housing (2). A sealing groove is provided around the second wire channel (23). An O-ring is installed in the sealing groove. The O-ring seals the junction between the second wire channel (23) and the third wire channel (111).

8. The quantitative electron beam alignment system for X-ray imaging according to claim 1, characterized in that: The fourth connecting member (10) is made of pure iron.

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