Electron beam generator and X-ray generator

Abstract

According to the present invention, an electron gun comprises a cathode that has a tip for emitting an electron beam, a first electrode that accommodates a portion including the tip of the cathode, and a second electrode that surrounds the first electrode when viewed from a direction along the emission axis of the electron beam. The first electrode has a first side wall that surrounds the portion including the tip around the emission axis. The second electrode has a second side wall that is separated from the first side wall and surrounds the first side wall. The first side wall is provided with a first opening that communicates a first space surrounded by the first side wall with a second space between the first side wall and the second side wall. The second electrode is provided with a second opening that is opened in a direction along the emission axis so as to communicate the second space with an external space.

Description

[Technical Field]

[0001] One aspect of the present disclosure relates to an electron beam generator and an X-ray generating device. [Background technology]

[0002] There is known an X-ray generating device that irradiates an electron beam onto a target. For example, Patent Document 1 discloses the configuration of an electron gun in which a cathode is housed in a Wehnelt electrode (grid electrode). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-041585 Summary of the Invention [Problem to be solved by the invention]

[0004] The Wehnelt electrode has an opening through which the electron beam passes, and the cathode is consumed by gas remaining in the space containing the cathode within the grid electrode.

[0005] This specification discloses an example of an electron beam generator and an X-ray generating device that includes a cathode accommodating space that can be efficiently evacuated. [Means for solving the problem]

[0006] An exemplary electron gun (electron beam generator) includes a cathode having a tip that emits an electron beam, a first electrode that houses the tip of the cathode, and a second electrode that surrounds the first electrode when viewed along the emission axis of the electron beam. The first electrode has a first sidewall that surrounds the tip around the emission axis. The second electrode has a second sidewall that is spaced apart from the first sidewall and surrounds the first sidewall. The first sidewall has a first opening that communicates a first space surrounded by the first sidewall with a second space between the first and second sidewalls. The second electrode has a second opening that opens in the direction along the emission axis to communicate the second space with an external space.

[0007] In some embodiments, a first space in the first electrode (i.e., a cathode housing space in which the cathode is housed) communicates with a second space between the first side wall and the second side wall through a first opening provided in the first side wall. Furthermore, the second space communicates with an external space through a second opening provided in the second electrode. This allows gas remaining in the cathode housing space to be discharged to the second space through the first opening, and the gas discharged to the second space to be discharged to the external space through the second opening. Therefore, the electron gun described above allows efficient evacuation of the cathode housing space.

[0008] The first opening may have an elongated hole shape extending in the circumferential direction around the emission axis in order to evacuate the first space.

[0009] The second sidewall may obscure the first opening when viewed from a direction perpendicular to the emission axis. In some embodiments, the edge of the first opening can be obscured from a structure with a large potential difference from the electron gun, such as an inner wall of a housing that houses the electron gun. This can suppress the occurrence of discharge.

[0010] The electron gun may further include a third electrode having a third sidewall surrounding a support that supports a tip of the cathode around the emission axis. The third sidewall may have a third opening that connects a third space surrounded by the third sidewall with an external space. In some embodiments, gas remaining in the cathode accommodation space (third space) that accommodates the support that supports the tip of the cathode can also be discharged to the external space through the third opening.

[0011] The electron gun may be provided with a through-hole that connects at least one of the first space and the second space with the third space. In some embodiments, the third space is connected to at least one of the first space and the second space for exhausting gas.

[0012] The second sidewall may surround the third sidewall around the emission axis. The second sidewall may have a fourth opening communicating a fourth space between the second sidewall and the third sidewall with an external space. The third space may communicate with the external space via the fourth space. In some embodiments, in a structure in which the second sidewall of the second electrode is arranged to surround the third sidewall of the third electrode, gas remaining in the third space can be discharged to the external space via the third opening, the fourth space, and the fourth opening.

[0013] The third opening and the fourth opening may be arranged so as not to face each other. By arranging the third opening and the fourth opening so that the third opening cannot be seen through the fourth opening, the edge portion and the like constituting the third opening can be concealed from a structure having a large potential difference with the electron gun, such as an inner wall of a housing that houses the electron gun. This makes it possible to suppress the occurrence of discharge.

[0014] An exemplary X-ray generator includes an electron gun having the configuration described above. [Effects of the Invention]

[0015] The embodiments disclosed herein allow for the space containing the cathode of an electron beam generator, such as an electron gun, to be evacuated. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram of an exemplary X-ray generating device. [Figure 2] FIG. 2 is a schematic cross-sectional view showing an example of the configuration of a magnetic lens in an X-ray generating device. [Figure 3] FIG. 3 is a front view of an exemplary magnetic quadrupole lens. [Figure 4] FIG. 4 is a schematic diagram of the configuration (doublet) of the example and comparative example including a magnetic focusing lens and a magnetic quadrupole lens. [Figure 5] FIG. 5 is a diagram showing an example of the relationship between the cross-sectional shape of an electron beam and the shape of the effective focal point of X-rays. [Figure 6] FIG. 6 is a perspective view of an exemplary electron beam generator, such as an electron gun. [Figure 7] FIG. 7 is a side view of the electron beam generator. [Figure 8] FIG. 8 is a side view of the electron beam generator. [Figure 9] FIG. 9 is a partial cross-sectional view of an electron beam generator. [Figure 10] FIG. 10 is a perspective view of the first grid electrode and the first hold electrode. [Figure 11] FIG. 11 is a cross-sectional view taken along line XI-XI in FIG. [Figure 12] FIG. 12 is a perspective view of the second retain electrode. [Figure 13] FIG. 13 is a cross-sectional view taken along line XIII-XIII in FIG. [Figure 14] FIG. 14 is a diagram showing a first modified example of a cylindrical tube. [Figure 15] FIG. 15 is a diagram showing a second modified example of the cylindrical tube. [Figure 16] FIG. 16 is a schematic diagram of an X-ray generating device according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0017] In the following description, the same or equivalent elements will be designated by the same reference numerals with reference to the drawings, and redundant description will be omitted.

[0018] 1, an exemplary X-ray generator 1 includes an electron gun 2, a rotating anode unit 3, a magnetic lens 4, an exhaust section 5, a housing 6 (first housing) that defines an internal space S1 that houses the electron gun 2, and a housing 7 (second housing) that defines an internal space S2 that houses the rotating anode unit 3. The housings 6 and 7 may be configured to be detachable from each other, may be integrally joined in a non-detachable manner, or may be formed integrally from the beginning.

[0019] The electron gun 2 emits an electron beam EB. The electron gun 2 has a cathode C that emits the electron beam EB. The cathode C is a circular, planar cathode that emits the electron beam EB having a circular cross-sectional shape. The cross-sectional shape of the electron beam EB is the cross-sectional shape in a direction perpendicular to the X-axis direction (first direction), which is a direction parallel to the traveling direction of the electron beam EB described below. In other words, the cross-sectional shape of the electron beam EB is the shape in the YZ plane. In order to form the electron beam EB having a circular cross-sectional shape, for example, the electron emission surface of the cathode C itself may have a circular shape when viewed from a position facing the electron emission surface of the cathode C (when the electron emission surface of the cathode C is viewed from the X-axis direction).

[0020] The rotary anode unit 3 includes a target 31, a rotary support 32, and a drive unit 33 that rotates the rotary support 32 around a rotation axis A. The target 31 is provided along the periphery of the rotary support 32, which is formed in a flat truncated cone shape with the rotation axis A as its central axis. The rotation axis A is the central axis of the rotary support 32, and the side surface of the truncated cone-shaped rotary support 32 has a surface that is inclined with respect to the rotation axis A. The rotary support 32 may also be formed in an annular shape with the rotation axis A as its central axis. The material that constitutes the target 31 is, for example, a heavy metal such as tungsten, silver, rhodium, molybdenum, or an alloy thereof. The rotary support 32 is rotatable around the rotation axis A. The material that constitutes the rotary support 32 is, for example, a metal such as copper or a copper alloy. The drive unit 33 has a drive source, for example, a motor, and drives the rotary support 32 to rotate around the rotation axis A. The target 31 receives the electron beam EB while rotating in accordance with the rotation of the rotary support 32, and generates X-rays XR. The X-rays XR are emitted to the outside of the housing 7 through an X-ray passage hole 7a formed in the housing 7. The X-ray passage hole 7a is airtightly sealed by a window member 8. The axial direction of the rotation axis A is parallel to the incident direction of the electron beam EB on the target 31. However, the rotation axis A may be inclined relative to the incident direction of the electron beam EB on the target 31 so as to extend in a direction intersecting the incident direction. The target 31 may be a so-called reflective type, and emits X-rays XR in a direction intersecting the traveling direction of the electron beam EB (the incident direction on the target 31). In some embodiments, the emission direction of the X-rays XR is a direction perpendicular to the traveling direction of the electron beam EB. Therefore, the direction parallel to the traveling direction of the electron beam EB is the X-axis direction (first direction), the direction parallel to the emission direction of the X-rays XR from the target 31 is the Z-axis direction (second direction), and the direction perpendicular to the X-axis and Z-axis directions is the Y-axis direction (third direction).

[0021] The magnetic lens 4 controls the electron beam EB. The magnetic lens 4 has a deflection coil 41, a magnetic focusing lens 42, a magnetic quadrupole lens 43, and a housing 44. The housing 44 houses the deflection coil 41, the magnetic focusing lens 42, and the magnetic quadrupole lens 43. The deflection coil 41, the magnetic focusing lens 42, and the magnetic quadrupole lens 43 are arranged in this order along the X-axis direction, from the electron gun 2 side toward the target 31 side. An electron passage P through which the electron beam EB passes is formed between the electron gun 2 and the target 31. As shown in FIG. 2 , the electron passage P may be formed by a cylindrical tube 9 (a cylindrical portion). The cylindrical tube 9 is a non-magnetic metal member extending along the X-axis direction between the electron gun 2 and the target 31. Additional exemplary configuration details of the cylindrical tube 9 will be described later.

[0022] The deflection coil 41, the magnetic focusing lens 42, and the magnetic quadrupole lens 43 are directly or indirectly connected to the cylindrical tube 9. For example, the deflection coil 41, the magnetic focusing lens 42, and the magnetic quadrupole lens 43 are assembled using the cylindrical tube 9 as a reference, so that their respective central axes are precisely arranged coaxially. As a result, the respective central axes of the deflection coil 41, the magnetic focusing lens 42, and the magnetic quadrupole lens 43 coincide with the central axis of the cylindrical tube 9 (an axis parallel to the X-axis).

[0023] The deflection coil 41 is disposed between the electron gun 2 and the magnetic focusing lens 42. The deflection coil 41 is disposed so as to surround the electron passage P. For example, the deflection coil 41 is indirectly connected to the cylindrical tube 9 via a cylindrical member 10. The cylindrical member 10 is a non-magnetic metal member extending coaxially with the cylindrical tube 9. The cylindrical member 10 is disposed so as to cover the outer periphery of the cylindrical tube 9. The deflection coil 41 is positioned by the surface of the wall portion 44a facing the target 31 and the outer circumferential surface of the cylindrical member 10. The wall portion 44a is a part of the housing 44 disposed at a position facing the internal space S1 and is made of a non-magnetic material. The deflection coil 41 adjusts the traveling direction of the electron beam EB emitted from the electron gun 2. The deflection coil 41 may be constituted by one (one set of) deflection coils or two (two sets of) deflection coils. In the former case where the deflection coil 41 includes one deflection coil, the deflection coil 41 may be configured to correct an angular deviation between the emission axis of the electron beam EB emitted from the electron gun 2 and the central axis (axis parallel to the X-axis) of the magnetic focusing lens 42 and the magnetic quadrupole lens 43. For example, an angular deviation may occur when the emission axis and the central axis intersect at a predetermined angle. Therefore, the angular deviation can be eliminated by changing the traveling direction of the electron beam EB with the deflection coil 41 to a direction along the central axis. In the latter case where the deflection coil 41 includes two deflection coils, two-dimensional deflection can be performed by the deflection coil 41. Therefore, not only the angular deviation but also a lateral deviation between the emission axis and the central axis (for example, when the emission axis and the central axis are parallel to each other in the X-axis direction and separated from each other in one or both of the Y-axis direction and the Z-axis direction) can be appropriately corrected.

[0024] The magnetic focusing lens 42 is disposed downstream of the electron gun 2 and the deflection coil 41. The magnetic focusing lens 42 focuses the electron beam EB by rotating the electron beam EB around an axis along the X-axis direction. For example, the electron beam EB passing through the magnetic focusing lens 42 is focused while rotating in a spiral. The magnetic focusing lens 42 includes a coil 42a arranged to surround the electron passage P, a pole piece 42b, a yoke 42c, and a yoke 42d. The yoke 42c also functions as a wall portion 44b of a housing 44 provided to connect a portion of the outer surface of the coil 42a to the cylindrical member 10. The yoke 42d is a cylindrical member provided to cover the outer periphery of the cylindrical member 10. For example, the coil 42a is indirectly connected to the cylindrical tube 9 via the cylindrical member 10 and the yoke 42d. The pole piece 42b is composed of the yoke 42c and the yoke 42d. The yokes 42c and 42d are made of a ferromagnetic material such as iron. The pole piece 42b may be formed by a notch (gap) provided between the yokes 42c and 42d and a portion of the yokes 42c and 42d located near the notch. The inner diameter D of the pole piece 42b is equal to the inner diameter of the gap-adjacent region of the yoke 42c or yoke 42d. As a result, the magnetic focusing lens 42 may be configured so that the magnetic field of the coil 42a leaks from the pole piece 42b toward the cylindrical tube 9.

[0025] The magnetic quadrupole lens 43 is disposed after the magnetic focusing lens 42. The magnetic quadrupole lens 43 deforms the cross-sectional shape of the electron beam EB into an elliptical shape having a major axis along the Z-axis direction and a minor axis along the Y-axis direction. The magnetic quadrupole lens 43 is disposed so as to surround the electron passage P. For example, the magnetic quadrupole lens 43 is indirectly connected to the cylindrical tube 9 via a wall portion 44c of the housing 44. The wall portion 44c is connected to the wall portion 44b and is disposed so as to cover the outer periphery of the cylindrical tube 9. The wall portion 44c is made of a non-magnetic metallic material.

[0026] As shown in FIG. 3 , the exemplary magnetic quadrupole lens 43 includes a circular yoke 43a, four cylindrical yokes 43b provided on the inner circumferential surface of the yoke 43a, and a yoke 43c provided at the tip of each yoke 43b. A coil 43d is wound around the yoke 43b. Each yoke 43c has a substantially semicircular cross-sectional shape in the YZ plane. The inner diameter d of the magnetic quadrupole lens 43 is the diameter of an inscribed circle passing through the innermost end of each yoke 43c. The magnetic quadrupole lens 43 functions as a concave lens in the XZ plane (a plane perpendicular to the Y-axis direction) and as a convex lens in the XY plane (a plane perpendicular to the Z-axis direction). This function of the magnetic quadrupole lens 43 adjusts the aspect ratio between the diameter of the electron beam EB along the Z-axis direction (major diameter X1) and the diameter of the electron beam EB along the Y-axis direction (minor diameter X2) so that the length of the electron beam EB along the Z-axis direction is greater than the length of the electron beam EB along the Y-axis direction. Therefore, the aspect ratio can be selectively adjusted by adjusting the amount of current flowing through the coil 43d. As an example, the aspect ratio of the major axis X1 to the minor axis X2 is adjusted to "10:1".

[0027] The exhaust unit 5 has a vacuum pump 5a (first vacuum pump) and a vacuum pump 5b (second vacuum pump). The housing 6 is provided with an exhaust passage E1 (first exhaust passage) for evacuating the space within the housing 6 (i.e., the internal space S1 defined by the housing 6 and the housing 44 of the magnetic lens 4). The vacuum pump 5b communicates with the internal space S1 via the exhaust passage E1. The housing 7 is provided with an exhaust passage E2 (second exhaust passage) for evacuating the space within the housing 7 (i.e., the internal space S2 defined by the housing 7). The vacuum pump 5a communicates with the internal space S2 via the exhaust passage E2. The vacuum pump 5b evacuates the internal space S1 via the exhaust passage E1. The vacuum pump 5a evacuates the internal space S2 via the exhaust passage E2. As a result, the internal spaces S1 and S2 are maintained in a vacuum state or a partial vacuum state, for example, to remove gas generated in the electron gun or the target. The internal pressure of the internal space S1 is preferably 10 -4 A partial vacuum of 10 Pa or less may be maintained, more preferably 10 -5The internal pressure of the internal space S2 may be maintained at a partial vacuum of 10 Pa or less. -6 Pa~10 -3 A partial vacuum may be maintained between Pa and Pa. The internal space of the cylindrical tube 9 (the space within the electron passage P) is also evacuated to a vacuum by the exhaust unit 5 via the internal space S1 or the internal space S2.

[0028] Instead of using two exhaust pumps, vacuum pump 5a and vacuum pump 5b, as in the configuration shown in FIG. 1, a structure (X-ray generator 1A) may be employed in which one exhaust pump (here, vacuum pump 5b is used as an example) can evacuate both the internal space S1 and the internal space S2, as shown in FIG. 8. In some embodiments, exhaust flow path E1 and exhaust flow path E2 may be connected by a communication path E3 located outside the housings 6 and 7. In another example, communication path E3 may include a through-hole extending from the inside of the wall of the housing 7 to the inside of the wall of the housing 6 so as to connect the exhaust flow path E1 and the exhaust flow path E2. Note that either vacuum pump 5a or vacuum pump 5b may be used as one exhaust pump, but using vacuum pump 5b connected to the exhaust flow path E1 as the exhaust pump enables more efficient evacuation.

[0029] In some embodiments, a voltage is applied to the electron gun 2 while the internal spaces S1, S2 and the electron passage P are evacuated. As a result, an electron beam EB having a circular cross section is emitted from the electron gun 2. The electron beam EB is focused on the target 31 by the magnetic lens 4 and deformed into an elliptical cross section, and then incident on the rotating target 31. When the electron beam EB is incident on the target 31, X-rays XR are generated in the target 31, and the X-rays XR having a substantially circular effective focal shape are emitted to the outside of the housing 7 through the X-ray passing hole 7a.

[0030] As shown in Fig. 2, the exemplary configuration of the cylindrical tube 9 has a shape in which the diameter changes stepwise along the X-axis direction. For example, the cylindrical tube 9 has six cylindrical portions 91 to 96 arranged along the X-axis direction. Each of the cylindrical portions 91 to 96 has a constant diameter along the X-axis direction. The outer diameter of the cylindrical tube 9 does not have to change in sync with the inner diameter of the cylindrical tube 9. In other words, the outer diameter of the cylindrical tube 9 may be constant.

[0031] The cylindrical portion 91 (first cylindrical portion) includes a first end 9a on the electron gun 2 side of the cylindrical tube 9. The cylindrical portion 91 extends from the first end 9a to a second end 91a surrounded by the portion of the coil 42a on the electron gun 2 side at the boundary portion 9c. The first end 92a of the cylindrical portion 92 (second cylindrical portion) is connected to the second end 91a on the target 31 side of the cylindrical portion 91. In some embodiments, the cylindrical portion 92 extends from the second end 91a of the cylindrical portion 91 to a second end 92b of the second cylindrical portion 92 that is slightly closer to the target 31 than the pole piece 42b. For example, the second end 92b of the second cylindrical portion 92 may be located between the pole piece 42b and the target 31 along the X-axis direction. Furthermore, the first end 93a of the cylindrical portion 93 (third cylindrical portion) is connected to the second end 92b on the target 31 side of the cylindrical portion 92.

[0032] The cylindrical portion 93 extends from the second end 92b of the cylindrical portion 92 to a second end 93b of the cylindrical portion 93 surrounded by the magnetic quadrupole lens 43. A first end of the cylindrical portion 94 (fourth cylindrical portion) is connected to a second end 93b of the cylindrical portion 93 on the target 31 side. The cylindrical portion 94 extends from the second end 93b of the cylindrical portion 93 to the housing 7 side of the wall portion 44c.

[0033] The cylindrical portion 95 (fifth cylindrical portion) and the cylindrical portion 96 (sixth cylindrical portion) pass through the inside of the wall portion 71 of the housing 7. The wall portion 71 is disposed opposite the target 31 and extends so as to intersect with the X-axis direction. The cylindrical portion 95 is connected to a second end of the cylindrical portion 94 on the target 31 side. The cylindrical portion 95 extends from the second end of the cylindrical portion 94 to a partway inside the wall portion 71. The cylindrical portion 96 is connected to an end of the cylindrical portion 95 on the target 31 side, partway inside the wall portion 71. The cylindrical portion 96 extends from the second end of the cylindrical portion 95 to a second end 9b of the cylindrical tube 9 on the target 31 side. As shown in FIG. 2 , the exemplary X-ray passing hole 7a is provided in the wall portion 72 that is connected to the wall portion 71 and extends so as to intersect with the Z-axis direction. The X-ray passing hole 7a penetrates the wall portion 72 along the Z-axis direction.

[0034] In some embodiments, when the diameters of the cylindrical portions 91 to 96 are represented as d1 to d6, the relationship of "d2>d3>d1>d4>d5>d6" holds. For example, the diameter d1 is 6 to 12 mm, the diameter d2 is 10 to 14 mm, the diameter d3 is 8 to 12 mm, the diameter d4 is 4 to 6 mm, the diameter d5 is 4 to 6 mm, and the diameter d6 is 0.5 to 4 mm.

[0035] At least a portion of the cylindrical portion 91 and the cylindrical portion 92 is located closer to the electron gun 2 than the portion of the electron path P surrounded by the pole piece 42b of the magnetic focusing lens 42 (particularly the gap between the yoke 42c and the yoke 42d). In some embodiments, at least a portion of the cylindrical portion 91 and the cylindrical portion 92 constitutes a "portion of the electron path P closer to the electron gun 2 than the portion surrounded by the pole piece 42b of the magnetic focusing lens 42" (hereinafter referred to as a "first cylindrical portion"). As described above, the diameter d2 of the cylindrical portion 92 is larger than the diameter d1 of the cylindrical portion 91 (d2>d1). In other words, the diameter of the cylindrical portion 92 is larger than the diameter of the cylindrical portion 91 adjacent to the electron gun 2. In other words, in the first cylindrical portion, at least a portion of the cylindrical portion 92 constitutes a diameter-increasing portion that expands toward the target 31.

[0036] The cylindrical portion 96 includes the end portion 9b on the target 31 side of the electron passage P. And the diameter d6 of the cylindrical portion 96 is smaller than the diameter d5 of the cylindrical portion 95 (d6 < d5). That is, the cylindrical portion 96 is reduced in diameter compared to the cylindrical portion 95 adjacent to the electron gun 2 side, and the cylindrical portion 96 constitutes a reduced-diameter portion that reduces in diameter toward the target 31 side. In some embodiments, the diameter d2 of the cylindrical portion 92 is the maximum diameter of the cylindrical tube 9, and it is sequentially reduced in diameter from the cylindrical portion 92 toward the target 31 side. Therefore, it can also be considered that the portion including the cylindrical portions 93 to 96 constitutes the reduced-diameter portion.

[0037] In some embodiments, the size of the electron beam EB is adjusted by the magnetic focusing lens 42 disposed downstream of the electron gun 2, and the cross-sectional shape of the electron beam EB is deformed into an elliptical shape by the magnetic quadrupole lens 43 disposed downstream of the magnetic focusing lens 42. Therefore, the adjustment of the size and the adjustment of the cross-sectional shape of the electron beam EB can be performed independently of each other.

[0038] FIG. 4A is a schematic diagram of an example configuration including the magnetic focusing lens 42 and magnetic quadrupole lens 43 shown in FIGS. 1 and 2. FIG. 4B is a schematic diagram of a comparative example configuration (doublet). FIGS. 4A and 4B are schematic diagrams of an example of an optical system acting on the electron beam EB between the cathode C (electron gun 2) and the target 31. In the comparative example configuration shown in FIG. 4B, the size and aspect ratio of the cross-sectional shape of the electron beam are adjusted by combining two stages of magnetic quadrupole lenses in which the surface acting as a concave lens and the surface acting as a convex lens are interchanged. In the comparative example of FIG. 4B, the lens that determines the size of the cross-sectional shape of the electron beam and the lens that determines the aspect ratio are not independent of each other. Therefore, the size and aspect ratio must be adjusted simultaneously by combining two stages of magnetic quadrupole lenses. This makes adjustment of the focal spot size and focal spot shape complicated. In contrast, in the configuration of the embodiment shown in FIG. 4A, the size of the cross-sectional shape of the electron beam EB is adjusted by the magnetic focusing lens 42 at the upstream stage. That is, the cross-sectional shape of the electron beam EB is narrowed down to a certain size by the magnetic focusing lens 42. Then, the aspect ratio of the cross-sectional shape of the electron beam EB is adjusted by the magnetic quadrupole lens 43 at the downstream stage. As described above, in the configuration of the embodiment shown in FIG. 4A, the lens (magnetic focusing lens 42) that determines the size of the cross-sectional shape of the electron beam EB and the lens (magnetic quadrupole lens 43) that determines the aspect ratio are independent of each other. This allows for easy and flexible adjustment of the focal spot size and focal spot shape.

[0039] Furthermore, the electron beam EB passing through the magnetic focusing lens 42 rotates around an axis along the X-axis direction. However, since the cross-sectional shape of the electron beam EB emitted by the electron gun 2 is circular, the cross-sectional shape of the electron beam passing through the magnetic focusing lens 42 and reaching the magnetic quadrupole lens 43 is constant (circular) regardless of the amount of rotation of the electron beam EB within the magnetic focusing lens 42. This allows the magnetic quadrupole lens 43 to consistently and reliably shape the cross-sectional shape F1 of the electron beam EB (cross-sectional shape along the YZ plane) into an elliptical shape having a major axis X1 along the Z direction and a minor axis X2 along the Y-axis direction. As a result, the aspect ratio and size of the cross-sectional shape of the electron beam EB can be easily and flexibly adjusted.

[0040] The performance of the X-ray generator 1 according to the embodiment, which includes the electron gun 2 and the magnetic lens 4, was evaluated through an experiment. A high voltage was applied to the electron gun 2, and the target 31 was grounded. At the desired output (voltage applied to the cathode C), X-rays XR with an effective focal spot size of 40 μm × 40 μm were obtained. When the focal spot size changed during 1000 hours of operation, the above effective focal spot size could be easily restored by simply adjusting the current flowing through the coil 43d of the magnetic quadrupole lens 43, without changing the operating conditions on the cathode C side. As described above, it was confirmed that the X-ray generator 1 allows the effective focal spot size of X-rays XR to be easily adjusted in response to dynamic changes simply by adjusting the current flowing through the coil 43d.

[0041] In some embodiments, as shown in FIG. 5 , the target 31 has an electron incident surface 31a onto which the electron beam EB is incident. The electron incident surface 31a is inclined with respect to the X-axis direction and the Z-axis direction. The cross-sectional shape F1 (i.e., the ratio of the major axis X1 to the minor axis X2) of the electron beam EB after being deformed into an elliptical shape by the magnetic quadrupole lens 43 and the inclination angle of the electron incident surface 31a with respect to the X-axis direction and the Y-axis direction are adjusted so that the focal shape F2 of the X-rays XR as viewed from the X-ray extraction direction (Z-axis direction) is substantially circular. In some embodiments, by adjusting the inclination angle of the electron incident surface 31a of the target 31 and the shaping conditions (aspect ratio) of the magnetic quadrupole lens 43, the shape of the focal point (effective focal point) of the extracted X-rays XR can be made substantially circular. As a result, an appropriate inspection image can be obtained in X-ray inspection, etc., using the X-rays XR generated by the X-ray generator 1.

[0042] In some embodiments, as shown in FIG. 2 , the length of the magnetic focusing lens 42 along the X-axis direction is longer than the length of the magnetic quadrupole lens 43 along the X-axis direction. Here, the "length of the magnetic focusing lens 42 along the X-axis direction" refers to the total length of the yoke 42c surrounding the coil 42a. In some embodiments, it becomes easier to ensure the number of turns of the coil 42a of the magnetic focusing lens 42. As a result, by generating a relatively large magnetic field in the magnetic focusing lens 42, the electron beam EB can be effectively focused to a small size to further increase the reduction ratio. Furthermore, to reduce the size of the electron beam EB incident on the electron incident surface 31a of the target 31, the distance from the electron gun 2 to the lens center (where the pole piece 42b is provided) formed by the magnetic focusing lens 42 can be increased.

[0043] Furthermore, the inner diameter D of the pole piece 42b of the magnetic focusing lens 42 is larger than the inner diameter d (see FIG. 3) of the magnetic quadrupole lens 43. In some embodiments, by making the inner diameter D of the pole piece 42b of the magnetic focusing lens 42 relatively large, the spherical aberration of the lens formed by the magnetic focusing lens 42 can be reduced. Furthermore, by making the inner diameter d of the magnetic quadrupole lens 43 relatively small, the number of turns of the coil 43d in the magnetic quadrupole lens 43 and the amount of current flowing through the coil 43d can be reduced. As a result, the amount of heat generated in the magnetic quadrupole lens 43 can also be suppressed.

[0044] The X-ray generator 1 also includes a cylindrical tube 9 that extends along the X-axis direction and forms an electron passage P through which the electron beam EB passes. The magnetic focusing lens 42 and the magnetic quadrupole lens 43 are directly or indirectly connected to the cylindrical tube 9. In some embodiments, the magnetic focusing lens 42 and the magnetic quadrupole lens 43 can be positioned or attached based on the cylindrical tube 9, so that the central axes of the magnetic focusing lens 42 and the magnetic quadrupole lens 43 can be precisely positioned coaxially. As a result, distortion of the profile (cross-sectional shape) of the electron beam EB after passing through the magnetic focusing lens 42 and the magnetic quadrupole lens 43 can be suppressed.

[0045] The X-ray generator 1 also includes a deflection coil 41. In some embodiments, as described above, it is possible to appropriately correct an angular deviation or the like that occurs between the emission axis of the electron beam EB emitted from the electron gun 2 and the central axes of the magnetic focusing lens 42 and the magnetic quadrupole lens 43. The deflection coil 41 is also disposed between the electron gun 2 and the magnetic focusing lens 42. In some embodiments, it is possible to appropriately adjust the traveling direction of the electron beam EB before the electron beam EB passes through the magnetic focusing lens 42 and the magnetic quadrupole lens 43. As a result, it is possible to maintain the cross-sectional shape of the electron beam EB incident on the target 31 in the intended elliptical shape.

[0046] In the X-ray generator 1, an electron passage P is formed between the housing 6 that houses the cathode C (electron gun 2) and the housing 7 that houses the target 31. The portion of the electron passage P, including the end on the target 31 side (end 9b of the cylindrical tube 9), tapers in diameter toward the target 31. In some embodiments, the cylindrical portion 96 (or the cylindrical portions 93 to 96) forms a tapered portion that tapers in diameter toward the target 31. This makes it difficult for reflected electrons generated by the electron beam EB being incident on the target 31 inside the housing 7 to reach the housing 6 via the electron passage P. As a result, deterioration of the cathode C caused by reflected electrons emitted from the target 31 can be suppressed or prevented. The reflected electrons are electrons that are incident on the target 31 and are reflected without being absorbed by the target 31.

[0047] When the electron beam EB is emitted from the cathode C, gas is generated by the electron gun 2. This gas may remain in the space housing the cathode C. Furthermore, gas (e.g., gas by-products such as H2, H2O, N2, CO, CO2, CH4, and Ar) may be generated within the housing 7 due to electron collisions with the target 31. This may cause electrons to be reflected from the surface of the target 31. In some embodiments, the entrance (i.e., end 9b) of the electron path P on the target 31 side is narrowed, so that less gas is drawn into the housing 6 (i.e., the internal space S1) through the electron path P, and less gas is discharged from the exhaust passage E1 provided in the housing 6. Therefore, in the X-ray generator 1, the housing 7 itself is provided with an exhaust passage (exhaust passage E2) for the gas. This allows the housings 6 and 7 to be appropriately evacuated while suppressing or preventing deterioration of the cathode C due to reflected electrons.

[0048] Furthermore, the portion of the electron path P closer to the electron gun 2 than the portion surrounded by the pole piece 42b of the magnetic focusing lens 42 (the first cylindrical portion described above) has an expanding diameter portion (at least a part of the cylindrical portion 92) that expands in diameter toward the target 31. In some embodiments, even if reflected electrons enter the electron path P from the end 9b of the electron path P on the target 31 side, the expanding diameter portion that expands in diameter toward the target 31 side (i.e., the portion that contracts in diameter toward the cathode C side) can suppress the movement of the reflected electrons through the electron path P toward the cathode C side. Furthermore, it is possible to effectively suppress the electron beam EB heading toward the target 31 from colliding with the inner wall of the electron path P (the inner surface of the cylindrical tube 9).

[0049] The expanded diameter portion includes a portion (i.e., a boundary portion between the cylindrical portions 91 and 92) where the diameter of the cylindrical tube 9 changes discontinuously from a portion having a diameter d1 (first diameter) (i.e., the cylindrical portion 91) toward the target 31 from a portion having a diameter d2 (second diameter) larger than the diameter d1 (i.e., the cylindrical portion 92). In some embodiments, the diameter of the cylindrical tube 9 changes in a stepped manner at the boundary portion between the cylindrical portions 91 and 92. The boundary portion 9c is formed by an annular wall having an inner diameter d1 and an outer diameter d2 (see FIG. 2). In some embodiments, even if there are reflected electrons traveling through the electron path P from the target 31 toward the electron gun 2, the reflected electrons can be made to collide with the boundary portion 9c. This more effectively suppresses or prevents the reflected electrons from moving toward the cathode C.

[0050] Furthermore, the diameter of the portion of the electron path P surrounded by the pole piece 42b of the magnetic focusing lens 42 (diameter d2 of the cylindrical portion 92) is equal to or greater than the diameter of the other portions of the electron path P. In other words, the electron path P has a maximum diameter in the portion surrounded by the pole piece 42b of the magnetic focusing lens 42. In some embodiments, by making the diameter of the portion where the electron beam EB emitted from the electron gun 2 expands larger (i.e., the portion surrounded by the pole piece 42b) larger than the diameter of the other portions, it is possible to effectively prevent the electron beam EB heading toward the target 31 from colliding with the inner wall of the electron path P (the inner surface of the cylindrical tube 9).

[0051] Furthermore, the exhaust flow path E1 and the exhaust flow path E2 are connected to each other. The exhaust unit 5 evacuates the inside of the housing 6 via the exhaust flow path E1, and also evacuates the inside of the housing 7 via the exhaust flow path E2. In some embodiments, the common exhaust unit 5 can evacuate both the internal space S1 in the housing 6 and the internal space S2 in the housing 7, thereby making it possible to reduce the size of the X-ray generator 1.

[0052] Next, the detailed configuration of the electron gun 2, which is an example of an electron beam generator, will be described with reference to Figures 6 to 13. As shown in Figures 6 to 13, the electron gun 2 has a cathode C, a first grid electrode 21 (first electrode), a first hold electrode 22, a second grid electrode 23 (second electrode), a second hold electrode 24, a third hold electrode 25 (third electrode), and a stem 26. One or both of the first grid electrode 21 and the second grid electrode 23 can be configured to control the amount of the electron beam EB emitted from the cathode C.

[0053] As shown in FIG. 9 , the cathode C has a tip portion C1 and a pair of support pins C2 (support portions). The tip portion C1 has an electron exit surface EE from which the electron beam EB is emitted. The pair of support pins C2 are electrically connected to the tip portion C1 and support the tip portion C1. The pair of support pins C2 may be formed of a conductive material such as metal. The tip portion C1 may also be formed in a cylindrical shape. In some embodiments, the electron exit surface EE, which is the tip surface of the tip portion C1, is formed in a circular flat shape. The electron beam EB is emitted from the electron exit surface EE of the tip portion C1 along the X-axis direction. The exit axis AX of the electron beam EB is an axis that passes through the center of the electron exit surface EE of the tip portion C1 and is parallel to the X-axis direction. In some embodiments, the exit axis AX is also the central axis of the electron gun 2. The pair of support pins C2 are held by a stem 26 made of an insulating material such as ceramic. The end of the support pin C2 opposite to the tip C1 is electrically connected to an external power supply device via a connection member or the like arranged in a space S13 surrounded by the third holding electrode 25.

[0054] 9 to 11, the first grid electrode 21 accommodates the tip C1 of the cathode C (the tip C1 and at least a portion of the tip C1 side of the pair of support pins C2). The first grid electrode 21 has a side wall 211 (first side wall), a top wall 212, and a bottom wall 213. The material of the first grid electrode 21 may be a metallic material with a high melting point (for example, titanium, molybdenum, or an alloy containing at least one of them).

[0055] The side wall 211 surrounds the tip C1 of the cathode C around the emission axis AX. In some embodiments, the side wall 211 is formed in a cylindrical shape with the emission axis AX as its central axis. An opening 211a (first opening) is provided in the side wall 211. Furthermore, a plurality of (for example, two) openings 211a are provided in the side wall 211 at equal intervals along the circumferential direction around the emission axis AX. In some embodiments, the two openings 211a are provided to face each other across the emission axis AX. Therefore, the two openings 211a may face each other in the Y-axis direction. Each opening 211a has a substantially rectangular elongated hole shape extending along the circumferential direction around the emission axis AX. Corners of each opening 211a have a curved shape (R-shape). A space S11 (first space) surrounded by the side wall 211 communicates with a space S12 (a space between the side wall 211 and a side wall 231 of the second grid electrode 23) described below through an opening 211a. The space S11 is surrounded by the side wall 211, a top wall 212, and a bottom wall 213. In some embodiments, the space S11 accommodates the tip portion C1 of the cathode C.

[0056] The top wall 212 is connected to the end of the side wall 211 on the target 31 side (electron emission direction side). The top wall 212 extends along a plane (YZ plane) perpendicular to the emission axis AX so as to cover the cathode C. A surface 212a of the top wall 212 on the target 31 side (electron emission direction side) is tapered so as to approach the target 31 side as it moves away from the emission axis AX. A circular opening 212b penetrating along the X-axis direction is provided in the center of the surface 212a. Therefore, the surface 212a forms a cone-shaped surface that slopes toward the opening 212b. The center of the opening 212b is located on the emission axis AX. The electron beam EB emitted from the electron emission surface EE of the tip C1 of the cathode C passes through the opening 212b. At least the electron emission surface EE of the tip C1 is located inside the opening 212b. In some embodiments, the tip C1 does not protrude further toward the target 31 (electron emission direction side) than the opening 212b, and therefore the electron emission surface EE does not protrude from the opening 212b.

[0057] The bottom wall 213 is connected to an end of the side wall 211 opposite to the end on the target 31 side (electron emission direction side). The bottom wall 213 extends along a plane (YZ plane) perpendicular to the emission axis AX. A pair of support pins C2 are provided in the center of the bottom wall 213 and pass through a circular opening 213a that penetrates the bottom wall 213 along the X-axis direction. The center of the opening 213a is located on the emission axis AX. The inner diameter of the opening 213a is larger than the inner diameter of the opening 212b. The bottom wall 213 has a flange portion 213b. The flange portion 213b is formed in an annular shape when viewed from the direction along the emission axis AX (X-axis direction), and extends outward from the side wall 211.

[0058] The first hold electrode 22 is a disk-shaped electrode connected to the first grid electrode 21. The first hold electrode 22 is made of a metal material with a high melting point (e.g., titanium, molybdenum, or an alloy containing at least one of them). The first hold electrode 22 is disposed on the side of the first grid electrode 21 opposite to the side where the target 31 is located (electron emission direction side). For example, the first hold electrode 22 is disposed along a surface 213c of the bottom wall 213 opposite to the target 31 side (electron emission direction side) so as to be in surface contact with the surface 213c. An opening 22a (central opening) penetrating in the X-axis direction is provided in the center of the first hold electrode 22. The center of the opening 22a is located on the emission axis AX. Furthermore, a circular through-hole H extending along the X-axis direction and communicating between the space S11 and a space S13 (described later) is provided in the bottom wall 213 and the first hold electrode 22. In some embodiments, a plurality of (for example, two) through holes H are provided at equal intervals along the circumferential direction around the emission axis AX. The two through holes H are provided to face each other across the emission axis AX. The two through holes H are provided to face each other in the Y-axis direction. The through hole H is composed of a through hole 213f provided in the bottom wall 213 and a through hole 22d provided in the first hold electrode 22 coaxially with the through hole 213f. In some embodiments, the through hole H that communicates with the space S11 and the space S13 is formed by the through hole 213f and the through hole 22d that overlap each other as viewed from the X-axis direction. As viewed from the X-axis direction, the outer edge of the first hold electrode 22 is located more inward than the outer edge of the flange portion 213b.

[0059] The stem 26 is a disk-shaped member that fixes the cathode C to the stem 26. The stem 26 has insertion holes through which a pair of support pins C2 serving as a power supply path are inserted. The stem 26 is made of an insulating material. The material of the stem 26 is, for example, alumina (Al2O3). The stem 26 is disposed within the opening 22a. The portion of the stem 26 that protrudes from the opening 22a is held by a second holding electrode 24, which will be described later.

[0060] The second hold electrode 24 is disposed on the side of the first hold electrode 22 opposite to the side where the target 31 is located (electron emission direction side). For example, the second hold electrode 24 is disposed along the surface 22b of the first hold electrode 22 opposite to the target 31 side (electron emission direction side) so as to be in surface contact with the surface 22b. The second hold electrode 24 is made of a metal material with a high melting point (e.g., an alloy of copper and molybdenum, an alloy of copper and tungsten, etc.). The second hold electrode 24 has a sidewall 241 and a flange portion 242. The sidewall 241 is formed in a cylindrical shape with the emission axis AX as its central axis. The flange portion 242 is annular and connected to the end of the sidewall 241 on the target side (electron emission direction side) and extends outside the sidewall 241 along a plane (YZ plane) perpendicular to the emission axis AX. The flange portion 242 is disposed along the surface 22b of the first retain electrode 22 so as to be in surface contact with the surface 22b. When viewed from the X-axis direction, the outer edge of the flange portion 242 is located more inward than the outer edge of the first retain electrode 22. In some embodiments, the outer edge of the flange portion 242 is located more inward than the edge of the through hole H on the emission axis AX side so that the flange portion 242 does not block the through hole H. The inner surface 241a of the side wall 241 is continuous with the opening 22a of the first retain electrode 22. The inner diameter of the side wall 241 is the same as the inner diameter of the opening 22a. The stem 26 is accommodated inside the opening 22a and the side wall 241. In some embodiments, the stem 26 is inserted into the opening 22a of the first retain electrode 22. Furthermore, the outer surface of the portion of the stem 26 protruding from the opening 22a is joined to the inner surface 241a of the side wall 241 of the second hold electrode 24, and the surface 22b of the first hold electrode 22 is joined to the flange portion 242. Therefore, the stem 26 can be selectively positioned and fixed to the electron gun 2.

[0061] 9 and 12, the third holding electrode 25 surrounds at least a portion (for example, a portion of the pair of support pins C2) of the cathode C. The third holding electrode 25 has a side wall 251 (third side wall) and a holding portion 252.

[0062] The side wall 251 is formed in a cylindrical shape with the emission axis AX as its central axis. An opening 251a (third opening) is provided in the side wall 251. In some embodiments, the side wall 251 is provided with a plurality of (for example, two) openings 251a. The two openings 251a face each other in a direction perpendicular to the emission axis AX (for example, the Z-axis direction). Corners of each opening 251a are formed in a substantially rectangular shape with a curved surface shape (R-shape). The length of a side of each opening 251a in a direction along the emission axis AX is substantially equal to the length of the side wall 251 in the direction along the emission axis AX. A space S13 (third space) surrounded by the side wall 251 and a space outside the side wall 251 (space S14 described later) are in communication with each other via the opening 251a.

[0063] The holder 252 has an annular shape and is connected to an end of the sidewall 251 on the target 31 side (electron emission direction side). The holder 252 holds the first hold electrode 22. The holder 252 has a portion 252a (first portion) on the target 31 side (electron emission direction side) and a portion 252b (second portion) opposite the target 31 side. The inner diameter of the portion 252a is approximately the same as the outer diameter of the first hold electrode 22. The inner diameter of the portion 252b is smaller than the inner diameter of the portion 252a and larger than the outer diameter of the flange portion 242 of the second hold electrode 24, and is sized so as not to block the through hole H. In some embodiments, the inner surface of the portion 252b is located outside the edge of the through hole H on the opposite side to the emission axis AX side. A side surface 22c of the first hold electrode 22 along the X-axis direction abuts against the inner surface of the portion 252a. An outer edge portion of the surface 22b of the first holding electrode 22 abuts against a surface 252c of the portion 252b on the target 31 side (electron emission direction side). In addition, an outer edge portion of the surface 22b of the first holding electrode 22 is placed on the surface 252c of the portion 252b.

[0064] 6 to 9, the second grid electrode 23 accommodates the cathode C, the first grid electrode 21, the first hold electrode 22, the second hold electrode 24, the third hold electrode 25, and the stem 26. The second grid electrode 23 is formed in a cylindrical shape with the emission axis AX as its central axis. In some embodiments, the second grid electrode 23 has a sidewall 231 (second sidewall) formed in a cylindrical shape with the emission axis AX as its central axis. The end of the sidewall 231 on the target 31 side (electron emission direction side) has a curved (R-shaped) surface.

[0065] The sidewall 231 has a cap-shaped surrounding portion 232 that surrounds (contains) the flange portion 213b of the first grid electrode 21 and the holding portion 252 of the third holding electrode 25. The surrounding portion 232 includes an end portion of the sidewall 231 on the target 31 side (electron emission direction side). The surrounding portion 232 has a portion 232a (first portion) on the target 31 side (electron emission direction side) and a portion 232b (second portion) on the opposite side from the target 31 side. The surrounding portion 232 is thicker than other portions of the sidewall 231 (for example, a portion where an opening 231b, described below, is provided). The thickness of the portion 232a is greater than the thickness of the portion 232b. In some embodiments, the sidewall 231 has a configuration in which the thickness of the portion (surrounding portion 232) including the end portion on the target 31 side (electron emission direction side) increases in a stepwise (step-like) manner toward the target 31 side. The inner diameter of the side wall 231 at the portion 232a is larger than the outer diameter of the side wall 211 of the first grid electrode 21 and smaller than the outer diameter of the flange portion 213b of the first grid electrode 21. The inner diameter of the side wall 231 at the other portion where the opening 231b is provided is the same as the outer diameter of the holding portion 252 of the third holding electrode 25.

[0066] The flange portion 213b is fixed by the portion 232a and the portion 232b of the surrounding portion 232. For example, the flange portion 213b is fixed by abutting a surface 213d of the flange portion 213b on the target 31 side (electron emission direction side) against a surface 232c of the portion 232a on the opposite side from the target 31 side. Furthermore, a side surface 213e of the flange portion 213b along the X-axis direction is surrounded by the inner surface of the portion 232b.

[0067] The holding part 252 is surrounded by the portion 232b of the surrounding part 232 and another portion of the side wall 231 where the opening 231b is provided. For example, a surface 252d of the holding part 252 on the target 31 side (electron emission direction side) is in contact with a surface 232d of the portion 232b on the opposite side from the target 31 side. In addition, an outer side surface 252e of the holding part 252 along the X-axis direction is surrounded by the inner surface of the other portion of the side wall 231.

[0068] The side wall 211 of the first grid electrode 21 and the side wall 231 (portion 232a of the surrounding portion 232) of the second grid electrode 23, which face each other, are separated from each other by a space S12 (second space). In some embodiments, the space S12 is an annular gap formed between the side wall 211 and the portion 232a. An opening 231a (second opening) opening in the X-axis direction is provided at the end of the side wall 231 on the target 31 side (i.e., the end of the portion 232a) so as to connect the space S12 to an external space of the electron gun 2 (for example, the internal space S1 of the housing 6). The end of the opening 231a on the target 31 side (electron emission direction side) has a curved (R-shaped) surface.

[0069] The side wall 231 is provided so as to cover the opening 211a of the first grid electrode 21 when viewed from a direction perpendicular to the X-axis direction (a direction along the YZ plane). As shown in Fig. 9, an end face 231c of the side wall 231 on the target 31 side (electron emission direction side) is located closer to the target 31 than the edge of the opening 211a on the target 31 side. Therefore, when the electron gun 2 is viewed from a direction perpendicular to the emission axis AX (for example, when viewed from the Y-axis or Z-axis direction), at least a part of the top wall 212 (the end on the target 31 side (electron emission direction side)) is visible, but the opening 211a covered by the second grid electrode 23 is not visible.

[0070] 13, a space S14 (fourth space) is formed between the side wall 251 and a portion of the side wall 231 facing the side wall 251 of the third hold electrode 25 (i.e., a portion surrounding the side wall 251). The side wall 231 and the side wall 251 are spaced apart so that a gap is provided between the side wall 231 and the side wall 251. An opening 231b (fourth opening) is provided in the portion of the side wall 231 facing the side wall 251 (a portion surrounding the side wall 251). In some embodiments, a plurality of openings 231b (two, for example) are provided in the side wall 231. The two openings 231b face each other in a direction perpendicular to the emission axis AX (for example, the Y-axis direction). Like the openings 251a, each opening 231b has a curved (R-shaped) edge and is formed in a substantially rectangular shape. A space S14 between the side wall 251 and the side wall 231 communicates with the external space of the electron gun 2 (for example, the internal space S1 of the housing 6) via the opening 231b.

[0071] 13, the opening 251a provided in the side wall 251 and the opening 231b provided in the side wall 231 do not directly face each other. In some embodiments, the position where the opening 251a is provided is shifted by approximately 90 degrees from the position where the opening 231b is provided when viewed from the X-axis direction. Therefore, the openings 231b and the openings 251a are arranged alternately so that the opening 251a cannot be seen through the opening 231b when the electron gun 2 is viewed from the outside.

[0072] In some embodiments, a space S11 within the first grid electrode 21 (a cathode accommodating space accommodating the tip portion C1 of the cathode C) communicates with a space S12 between the side wall 211 of the first grid electrode 21 and a side wall 231 (a portion 232a of the surrounding portion 232) of the second grid electrode 23 through an opening 211a formed in the side wall 211 of the first grid electrode 21. Furthermore, the space S12 communicates with an external space of the electron gun 2 (e.g., the internal space S1 of the housing 6) through an opening 231a formed in the second grid electrode 23. As a result, gas remaining in the cathode accommodating space (space S11) is discharged to the space S12 through the opening 211a, and the gas discharged to the space S12 is discharged to an external space of the electron gun 2 (e.g., the internal space S1 of the housing 6) through the opening 231a. Therefore, the electron gun 2 can be used to efficiently evacuate the cathode accommodating space (space S11). Furthermore, gas may also be generated from the components (for example, the first grid electrode 21) that make up the electron gun 2, but this gas can also be efficiently exhausted. In this way, the electron gun 2 is configured to efficiently evacuate the cathode housing space (space S11), and wear on the cathode C and discharge between components (for example, corona discharge between the support pin C2 and each electrode) can be suppressed.

[0073] The opening 211a has an elongated hole shape extending in the circumferential direction around the emission axis AX in order to evacuate the space S11 via the opening 211a.

[0074] The side wall 231 may be configured to cover the opening 211a when viewed from a direction perpendicular to the emission axis AX (a direction along the YZ plane). The edges and the like that form the opening 211a can be hidden from structures that have a large potential difference with the electron gun, such as the inner wall of the housing 6. This makes it possible to suppress the occurrence of discharge.

[0075] The third holding electrode 25 has a sidewall 251 that surrounds a support portion (a pair of support pins C2) that supports the tip portion C1 of the cathode C around the emission axis AX. The sidewall 251 has an opening 251a that connects a space S13 surrounded by the sidewall 251 to an external space of the electron gun 2 (for example, the internal space S1 of the housing 6). This allows gas remaining in the cathode housing space (space S13) that houses the pair of support pins C2 to be discharged to the external space of the electron gun 2 (for example, the internal space S1 of the housing 6) through the opening 251a. Gas may also be generated from each component (for example, the third holding electrode 25) that configures the electron gun 2, and this configuration allows efficient discharge of such gas.

[0076] A through hole H that connects the space S11 and the space S13 may be provided in the electron gun 2. According to the above configuration, the space S13 can be evacuated more effectively.

[0077] In some embodiments, a portion of the sidewall 231 surrounds the sidewall 251 around the emission axis AX. The portion of the sidewall 231 surrounding the sidewall 251 has an opening 231b that connects a space S14 between the sidewalls 231 and 251 to an external space of the electron gun 2 (e.g., the internal space S1 of the housing 6). The space S13 communicates with the external space of the electron gun 2 (e.g., the internal space S1 of the housing 6) via the space S14. This allows gas remaining in the space S13 to be discharged to the external space of the electron gun 2 (e.g., the internal space S1 of the housing 6) through the opening 251a, the space S14, and the opening 231b, even in a structure in which the sidewall 231 of the second grid electrode 23 is disposed so as to surround the sidewall 251 of the third holding electrode 25. Furthermore, gas may also be generated from each component (e.g., the third holding electrode 25) constituting the electron gun 2, and this gas can be efficiently discharged.

[0078] The opening 251a and the opening 231b are arranged so as not to face each other. The opening 251a and the opening 231b are arranged so that the opening 251a cannot be seen through the opening 231b, and this allows the edge portion and the like constituting the opening 251a to be hidden from structures having a large potential difference with the electron gun, such as the inner wall of the housing 6. This makes it possible to suppress the occurrence of discharge.

[0079] An evaluation experiment using the X-ray generator 1 according to the embodiment, which is equipped with the electron gun 2, confirmed that no discharge occurs at a tube voltage of 160 kV after conditioning. Furthermore, it was confirmed that, as a result of no discharge occurring, the amount of wear of the cathode crystal constituting the cathode C can be significantly reduced compared to when a configuration is adopted that does not include the openings 211a, 231a, 251a, and 231b.

[0080] It should be understood that not all aspects, advantages, and features described herein are necessarily achieved by or included in any particular embodiment. While various embodiments have been described herein, it should be apparent that other embodiments, including those having different materials and configurations, may be employed.

[0081] For example, if the emission axis of the electron beam EB from the electron gun 2 is precisely aligned with the central axis of the magnetic focusing lens 42, the deflection coil 41 may be omitted. Moreover, the deflection coil 41 may be disposed between the magnetic focusing lens 42 and the magnetic quadrupole lens 43, or between the magnetic quadrupole lens 43 and the target 31.

[0082] The shape of the electron passage P (cylindrical tube 9) may have a uniform diameter throughout. Alternatively, the electron passage P may be formed by a single cylindrical tube 9. In another example, the cylindrical tube 9 may be provided only within the housing 6, and the electron passage P passing through the housing 7 may be formed by a through-hole provided in the wall 71 of the housing 7. Alternatively, the electron passage P may be formed by the through-hole of the tubular member 10 and the through-holes provided in the housing 44 and the housing 7, without providing a separate cylindrical tube 9.

[0083] FIG. 6 shows a first modified example of the cylindrical tube (cylindrical tube 9A). In some embodiments, the cylindrical tube 9A differs from the cylindrical tube 9 shown in FIG. 2 in that it has cylindrical portions 91A to 93A instead of the cylindrical portions 91 to 96. The cylindrical portion 91A extends from the end 9a of the cylindrical tube 9 to a position surrounded by the electron gun 2 side of the coil 42a. The cylindrical portion 91A has a tapered shape. For example, the diameter of the cylindrical portion 91A gradually increases from diameter d1 to diameter d2 from the end 9a toward the target 31. The cylindrical portion 92A extends from the end of the cylindrical portion 91A on the target 31 side to a position slightly closer to the target 31 than the pole piece 42b. The cylindrical portion 92A has a constant diameter (diameter d2). The cylindrical portion 93A extends from the end of the cylindrical portion 92A on the target 31 side to the end 9b of the cylindrical tube 9. The cylindrical portion 93A has a tapered shape. For example, the diameter of cylindrical portion 93A gradually decreases from diameter d2 to diameter d6 from the end of cylindrical portion 92A toward target 31. In cylindrical tube 9A, cylindrical portion 91A corresponds to the expanded diameter portion, and cylindrical portion 93A corresponds to the reduced diameter portion.

[0084] FIG. 7 shows a second modified example of the cylindrical tube (cylindrical tube 9B). In some embodiments, the cylindrical tube 9B differs from the cylindrical tube 9 shown in FIG. 2 in that it includes cylindrical portions 91B and 92B instead of the cylindrical portions 91 to 96. The cylindrical portion 91B extends from the end 9a of the cylindrical tube 9 to a position surrounded by the pole piece 42b. The cylindrical portion 91B has a tapered shape. For example, the diameter of the cylindrical portion 91B gradually increases from diameter d1 to diameter d2 from the end 9a toward the target 31. The cylindrical portion 92B extends from the end of the cylindrical portion 91B facing the target 31 to the end 9b of the cylindrical tube 9. The cylindrical portion 92B has a tapered shape. In some embodiments, the diameter of the cylindrical portion 92B gradually decreases from diameter d2 to diameter d6 from the end of the cylindrical portion 91B toward the target 31. In the cylindrical tube 9B, the cylindrical portion 91B corresponds to the expanded diameter portion, and the cylindrical portion 92B corresponds to the contracted diameter portion.

[0085] In some embodiments, the reduced diameter portion and the expanded diameter portion of the cylindrical tube (electron path) do not have to be formed in a stepped (discontinuous) manner as in cylindrical tube 9, but may be formed in a tapered manner as in cylindrical tubes 9A and 9B. Also, as in cylindrical tube 9B, the cylindrical tube may be formed only with a tapered portion. Also, the cylindrical tube may have both a portion where the diameter changes in a stepped manner and a portion where the diameter changes in a tapered manner. For example, the expanded diameter portion may be formed in a tapered manner as in cylindrical tube 9A, while the reduced diameter portion may be formed in a stepped manner as in cylindrical tube 9.

[0086] Furthermore, the target does not have to be a rotating anode. In some embodiments, the target may be configured not to rotate, and the electron beam EB may be configured to always be incident on the same position on the target. However, by using the target as a rotating anode, it is possible to reduce the local load on the target caused by the electron beam EB. As a result, it is possible to increase the amount of the electron beam EB and increase the dose of X-rays XR emitted from the target.

[0087] In some embodiments, the electron gun 2 may be configured to emit an electron beam EB having a circular cross-sectional shape, or in other examples, the electron gun 2 may be configured to emit an electron beam having a cross-sectional shape other than circular.

[0088] In some embodiments, the electron gun 2 may not be provided with all of the openings 211a, 231a, 251a, and 231b described above. For example, the openings 251a and 231b may be omitted. Even in this case, the openings 211a and 231a can improve the exhaust efficiency of the space S11. The shape, number, and arrangement of one or more of the openings 211a, 231a, 251a, and 231b and the through-hole H may be changed. The through-hole H may connect the space S12 and the space S13. The position where the through-hole H is formed may be a position overlapping the space S12 when viewed from the X-axis direction (i.e., a position outside the position shown in FIG. 9 and away from the emission axis AX).

[0089] [Configuration 1] The first electrode includes a first grid electrode 21 , the second electrode includes a second grid electrode 23 , and the third electrode includes a retaining electrode 25 .

[0090] [Configuration 2] The electron gun 2 further includes a first hold electrode 22 connected to the first grid electrode 21 and a second hold electrode 24 connected to the first hold electrode 22. The first hold electrode 22 is located between the first grid electrode 21 and the second hold electrode 24.

[0091] [Configuration 3] The first holding electrode 22 has a disk-shaped metal electrode.

[0092] [Configuration 4] The first hold electrode 22 has a plurality of circular through-holes 22d provided at equal intervals along the circumferential direction around the emission axis AX.

[0093] [Configuration 5] The plurality of circular through holes 22d communicates at least one of the first space (space S11) and the second space (space S12) with the third space (space S13).

[0094] [Configuration 6] The second holding electrode 24 has a cylindrical side wall 241 and an annular flange portion 242 .

[0095] [Configuration 7] The outer edge of the annular flange portion 242 is located inside the edge of at least one circular through-hole 22d.

[0096] [Configuration 8] A central opening (opening 22a) located on the emission axis AX is provided in the first holding electrode 22. The electron gun 2 further includes a stem 26 that supports the cathode C and is inserted into the central opening (opening 22a).

[0097] [Configuration 9] The second holding electrode 24 has a cylindrical side wall 241. The outer surface of the stem 26 protruding from the central opening (opening 22a) is joined to the inner surface 241a of the cylindrical side wall 241.

[0098] [Configuration 10] A second space (space S12) located between the first side wall 211 and the second side wall 231 forms an annular gap.

[0099] [Configuration 11] The tip C1 of the cathode C is located in the first space (space S11).

[0100] [Configuration 12] The tip C1 of the cathode C emits an electron beam EB into the external space (the internal space S1 of the housing 6).

Claims

1. An X-ray generating device comprising an electron beam generator, The electron beam generator includes: a cathode having a tip that emits an electron beam; a first electrode that houses the tip portion of the cathode and has a first side wall that surrounds the tip portion around the emission axis of the electron beam, and a top wall that is connected to an end of the first side wall on the electron emission direction side of the electron beam; a second electrode surrounding the first electrode when viewed from a direction along the emission axis and having a second sidewall spaced apart from the first sidewall and surrounding the first sidewall; a first opening is provided in the first side wall, the first opening communicating a first space surrounded by the first side wall with a second space between the first side wall and the second side wall; the second electrode is provided with a second opening that opens in a direction along the emission axis so that the second space is not covered by the second electrode in the direction along the emission axis, and that connects the second space with an external space of the electron beam generator; the top wall of the first electrode protrudes toward the electron emission direction beyond an end face of the second side wall on the electron emission direction side, and has an inclined surface that is tapered so as to approach the electron emission direction as it becomes farther away from the emission axis on the electron emission direction side.

2. The X-ray generating device according to claim 1 , wherein the first opening has an elongated hole shape extending in a circumferential direction around the emission axis.

3. The X-ray generating device according to claim 1 , wherein the second side wall is configured to cover and conceal the first opening when viewed from a direction perpendicular to the emission axis.

4. a third electrode having a third side wall surrounding a support portion that supports the tip portion of the cathode around the emission axis; The X-ray generating device according to claim 1 , wherein the third side wall is provided with a third opening that connects a third space surrounded by the third side wall with the external space.

5. The X-ray generating device according to claim 4 , further comprising a through-hole that connects at least one of the first space and the second space with the third space.

6. the first electrode includes a first grid electrode; The X-ray generating device according to claim 4 , wherein the second electrode includes a second grid electrode.

7. a first holding electrode connected to the first grid electrode; a second hold electrode connected to the first hold electrode; 7. The X-ray generating device of claim 6, wherein the first hold electrode is located between the first grid electrode and the second hold electrode.

8. The X-ray generating device according to claim 7 , wherein the first holding electrode has a disk-shaped metal electrode.

9. The X-ray generating device according to claim 7 , wherein the first holding electrode has a plurality of circular through holes provided at equal intervals along a circumferential direction around the emission axis.

10. The X-ray generating device according to claim 9 , wherein the plurality of circular through-holes connect at least one of the first space and the second space with the third space.

11. 10. The X-ray generating device according to claim 9, wherein the second holding electrode has a cylindrical side wall and an annular flange portion.

12. The X-ray generating device according to claim 11 , wherein an outer edge of the annular flange portion is located inside an edge of at least one of the circular through-holes.

13. the first retaining electrode is provided with a central opening positioned on the emission axis, 8. The x-ray generating device of claim 7, further comprising a stem supporting the cathode and inserted into the central opening.

14. the second retaining electrode has a cylindrical sidewall; 14. The x-ray generating device of claim 13, wherein an outer surface of the stem protruding from the central opening is joined to an inner surface of the cylindrical side wall.

15. The X-ray generating device according to claim 1 , wherein the second space located between the first side wall and the second side wall forms an annular gap.

16. The X-ray generating device according to claim 1 , wherein the tip of the cathode is located in the first space.

17. The X-ray generating device according to claim 1 , wherein the tip of the cathode emits the electron beam into the external space.

18. 1. An electron beam generator comprising: a cathode having a tip that emits an electron beam; a first electrode that houses the tip of the cathode and has a first sidewall that surrounds the tip around the emission axis of the electron beam; a second electrode surrounding the first electrode when viewed from a direction along the emission axis and having a second sidewall spaced apart from the first sidewall and surrounding the first sidewall; a third electrode having a third side wall surrounding a support portion that supports the tip portion of the cathode around the emission axis; a fourth opening provided in a portion of the second side wall surrounding the third side wall, the fourth opening communicating a fourth space between the second side wall and the third side wall with an external space of the electron beam generator; a first opening is provided in the first side wall, the first opening communicating a first space surrounded by the first side wall with a second space between the first side wall and the second side wall; the second electrode is provided with a second opening that opens in a direction along the emission axis and connects the second space to the external space; a third opening portion is provided in the third side wall, the third opening portion communicating a third space surrounded by the third side wall with the external space; The third space and the external space communicate with each other via the fourth space.

19. 20. The electron beam generator of claim 18, wherein the third opening and the fourth opening do not face each other.

20. An electron beam generator comprising: a cathode having a tip that emits an electron beam; a first electrode that houses the tip portion of the cathode and has a first side wall that surrounds the tip portion around the emission axis of the electron beam, and a top wall that is connected to an end of the first side wall on the electron emission direction side of the electron beam; a second electrode surrounding the first electrode when viewed from a direction along the emission axis and having a second sidewall spaced apart from the first sidewall and surrounding the first sidewall; a third electrode having a third side wall surrounding a support portion that supports the tip portion of the cathode around the emission axis, a first opening is provided in the first side wall, the first opening communicating a first space surrounded by the first side wall with a second space between the first side wall and the second side wall; the second electrode is provided with a second opening that opens in a direction along the emission axis so that the second space is not covered by the second electrode in the direction along the emission axis, and that connects the second space with an external space of the electron beam generator; the top wall of the first electrode protrudes toward the electron emission direction further than an end face of the second side wall on the electron emission direction side, and has an inclined surface that is tapered so as to approach the electron emission direction side as it becomes farther away from the emission axis on the electron emission direction side, The electron beam generator, wherein the third side wall is provided with a third opening that connects a third space surrounded by the third side wall with the external space.

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