X-ray source

Abstract

This X-ray source comprises: a photoelectric surface that emits photoelectrons in response to incidence of pulsed light; a target that generates X-rays in response to incidence of the photoelectrons emitted from the photoelectric surface; and a control electrode unit disposed between the photoelectric surface and the target. The control electrode unit has: a focusing electrode that is disposed so as to face the photoelectric surface and focuses the photoelectrons emitted from the photoelectric surface; and an acceleration electrode that is disposed between the focusing electrode and the target and accelerates the photoelectrons.

Description

X-ray source

[0001] One aspect of the present disclosure relates to an X-ray source.

[0002] Patent Document 1 describes an X-ray generating tube (X-ray source) including a photoelectron emission layer, an acceleration mesh arranged in parallel with the photoelectron emission layer, and a cylindrical focusing electrode arranged downstream of the acceleration mesh (Fig. 5).

[0003] Japanese Patent Application Laid-Open No. 60-47355

[0004] In an X-ray source as described above, for example, when micro-focusing to reduce the focal size of the output X-rays is required, it may be necessary to focus the photoelectrons well.

[0005] One aspect of the present disclosure aims to provide an X-ray source capable of focusing photoelectrons well.

[0006] The X-ray source according to one aspect of the present disclosure is [1] "a photocathode that emits photoelectrons in response to the incidence of light, a target that generates X-rays in response to the incidence of the photoelectrons emitted from the photocathode, and a control electrode portion arranged between the photocathode and the target, the control electrode portion being arranged to face the photocathode, the focusing electrode that focuses the photoelectrons emitted from the photocathode, and an acceleration electrode arranged between the focusing electrode and the target and accelerating the photoelectrons, an X-ray source".

[0007] In this X-ray source, the focusing electrode is arranged to face the photocathode, and the acceleration electrode is arranged between the focusing electrode and the target. That is, the acceleration electrode is arranged downstream of the focusing electrode in the traveling direction of the photoelectrons with respect to the focusing electrode. Thereby, it is possible to focus the photoelectrons having a relatively low energy before being accelerated by the acceleration electrode, and it is possible to focus the photoelectrons well.

[0008] The X-ray source according to one aspect of the present disclosure may be [2] "the X-ray source according to [1], wherein the acceleration electrode is arranged so as to overlap a part of the focusing electrode in a direction perpendicular to the direction in which the focusing electrode faces the photocathode". In this case, the acceleration electrode can be brought closer to the focusing electrode, and the photoelectrons can be accelerated well.

[0009] An X-ray source relating to one aspect of this disclosure may be [3] "the X-ray source according to [1] or [2], wherein the focusing electrode has a cylindrical portion having a center line along the direction in which the focusing electrode faces the photocathode, and the accelerating electrode is arranged inside the cylindrical portion of the focusing electrode." In this case, the accelerating electrode can be brought closer to the focusing electrode, and photoelectrons can be accelerated effectively.

[0010] An X-ray source relating to one aspect of this disclosure may be [4] "the X-ray source according to any one of [1] to [3], wherein the accelerating electrode has a cylindrical portion having a center line aligned in the direction in which the focusing electrode faces the photocathode." In this case, for example, compared to the case in which the accelerating electrode is formed by a flat mesh electrode, the electric field formed by the accelerating electrode can be made uniform, and unevenness in the trajectory of photoelectrons can be suppressed. In addition, since photoelectrons do not collide with the mesh electrode and disappear, the loss of photoelectrons can be suppressed.

[0011] An X-ray source relating to one aspect of this disclosure may be [5] "the X-ray source according to [4], wherein the surface of the focusing electrode facing the accelerating electrode has a first curved surface that curves inward toward the opposite side of the accelerating electrode, and the cylindrical portion of the accelerating electrode has a second curved surface that is arranged to face the first curved surface and curves toward the first curved surface." In this case, the generation of discharge between the focusing electrode and the accelerating electrode can be suppressed.

[0012] An X-ray source relating to one aspect of this disclosure may be [6] "the X-ray source according to [4], wherein the surface of the focusing electrode facing the accelerating electrode has a first inclined surface that is inclined to move away from the center line of the focusing electrode as it approaches the accelerating electrode, and the cylindrical portion of the accelerating electrode has a second inclined surface that is arranged to face the first inclined surface and is inclined to move away from the center line of the accelerating electrode as it moves away from the focusing electrode." In this case, the generation of discharge between the focusing electrode and the accelerating electrode can be suppressed.

[0013] An X-ray source relating to one aspect of this disclosure may be [7] "an X-ray source according to any one of [1] to [6] wherein the photocathode is curved so as to be concave toward the opposite side from the focusing electrode." In this case, photoelectrons can be emitted in a state that is easily focused.

[0014] An X-ray source relating to one aspect of this disclosure may be [8] "the X-ray source according to [7], wherein the surface of the focusing electrode facing the photocathode is curved to follow the photocathode." In this case, the photoelectrons emitted from the photocathode can be focused even more effectively.

[0015] An X-ray source relating to one aspect of the present disclosure may be [9] "the X-ray source according to [4], wherein the space inside the cylindrical portion of the accelerating electrode comprises a cylindrical first space located on the side of the focusing electrode and a second space located on the target side relative to the first space and having a larger diameter than the first space." In this case, the formation of the second space makes it possible to suppress photoelectrons traveling through the internal space of the cylindrical portion from coming into contact with the wall surface of the cylindrical portion.

[0016] An X-ray source relating to one aspect of this disclosure may be

[10] "the X-ray source according to [3], wherein the accelerating electrode has a cylindrical portion having a center line aligned in the direction in which the focusing electrode faces the photocathode, a first ventilation hole is formed in the cylindrical portion of the focusing electrode, a second ventilation hole is formed in the cylindrical portion of the accelerating electrode, and the space inside the cylindrical portion of the accelerating electrode is connected to the space outside the cylindrical portion of the focusing electrode via the first ventilation hole and the second ventilation hole." In this case, the inside of the X-ray source can be well vacuumed.

[0017] An X-ray source relating to one aspect of the present disclosure may be

[11] "an X-ray source according to any one of [1] to

[10] , wherein a cylindrical metal member having a center line aligned with the direction in which the focusing electrode faces the photocathode is arranged between the accelerating electrode and the target, the cylindrical member having the same potential throughout, and defining an equipotential space through which the photoelectrons pass." In this case, for example, an equipotential space can be provided that can be used for deflecting the direction of propagation of photoelectrons emitted from the photocathode toward the target, or ions generated in the target when photoelectrons are incident and traveling from the target toward the photocathode.

[0018] An X-ray source relating to one aspect of this disclosure may be

[12] "the X-ray source according to

[11] , further comprising a deflector that deflects the direction of propagation of photoelectrons emitted from the photocathode toward the target, or ions generated in the target when photoelectrons are incident, toward the photocathode from the target, in the equipotential space." In this case, damage to the photocathode due to ion collisions can be suppressed.

[0019] An X-ray source relating to one aspect of this disclosure may be

[13] "the X-ray source according to

[12] , wherein the deflector has either a deflection plate that generates an electric field for deflecting the direction of propagation of the photoelectrons or ions, or a coil that generates a magnetic field for deflecting the direction of propagation of the photoelectrons or ions." In this case, damage to the photocathode due to ion collisions can be suppressed by the electric or magnetic field.

[0020] An X-ray source relating to one aspect of the present disclosure may be

[14] "the X-ray source according to

[13] , wherein the deflector has a pair of deflection plates, and the pair of deflection plates are arranged to face each other in a direction perpendicular to the direction in which the focusing electrode faces the photocathode." In this case, the direction of propagation of photoelectrons or ions can be deflected by the electric field generated by the pair of deflection plates.

[0021] An X-ray source relating to one aspect of this disclosure may be

[15] "the X-ray source according to

[14] , wherein the pair of deflection plates are inclined with respect to the direction in which the focusing electrode faces the photocathode, such that they move away from each other as they move toward the target." In this case, the direction of propagation of photoelectrons or ions can be deflected by the electric field generated by the pair of deflection plates. Furthermore, it is possible to suppress the deflected photoelectrons from coming into contact with the deflection plates.

[0022] An X-ray source relating to one aspect of this disclosure may be the X-ray source according to

[16] "the deflector having a pair of coils, the pair of coils being arranged to face each other in a direction perpendicular to the direction in which the focusing electrode faces the photocathode." In this case, the direction of propagation of photoelectrons or ions can be deflected by the magnetic field generated by the pair of coils.

[0023] An X-ray source relating to one aspect of this disclosure may be

[17] "the X-ray source according to

[12] , further comprising a light source that outputs pulsed light toward the photocathode at a predetermined timing, and a control unit that controls the light source and the deflector, wherein the control unit controls the deflector so as to deflect the direction of propagation of the photoelectrons or ions during either a first time period from when the photoelectrons are emitted from the photocathode by the incidence of the pulsed light until the photoelectrons are incident on the target, or a second time period from when the photoelectrons are incident on the target until the next pulsed light is incident on the photocathode." In this case, when X-rays are generated using pulsed light, damage to the photocathode due to ion collisions can be suppressed.

[0024] An X-ray source relating to one aspect of this disclosure may be

[18] "the X-ray source according to

[17] , wherein the control unit controls the deflector so that the deflector deflects the direction of propagation of the photoelectrons or ions in the first time period." In this case, since photoelectrons accelerated by the accelerating electrode are easier to deflect than ions generated in the target, the photoelectrons can be easily deflected.

[0025] According to one aspect of this disclosure, it is possible to provide an X-ray source that can focus photoelectrons well.

[0026] This is a perspective view of an X-ray source according to an embodiment. This is a cross-sectional view of the X-ray source in Figure 1. This is an enlarged view of a part of the cross-sectional view in Figure 2. (a) and (b) are diagrams to illustrate the flexibility of photoelectrons. (a) and (b) are diagrams to illustrate the case in which photoelectrons are accelerated by a mesh electrode. This is a cross-sectional view of an X-ray source according to a first modification. (a) and (b) are diagrams to illustrate the case in which the direction of ion propagation is deflected by a deflection plate. (a) and (b) are diagrams to illustrate the case in which the direction of photoelectron propagation is deflected by a deflection plate. This is a diagram showing the deflection plate in an inclined position. This is a cross-sectional view of an X-ray source according to a second modification. (a) and (b) are diagrams showing an example of the coil arrangement in Figure 10.

[0027] The embodiments of this disclosure will be described in detail below with reference to the drawings. In the following description, the same or equivalent elements will be denoted by the same reference numerals, and redundant descriptions will be omitted. [Embodiments]

[0028] As shown in Figures 1 to 3, the X-ray source 1 comprises an X-ray generating unit 2, a photoelectron generating unit 3, a light source 4, and a control unit 5. The X-ray source 1 is, for example, a pulsed X-ray source that generates pulsed X-rays. The X-ray source 1 is used, for example, for X-ray imaging and scientific measurements using X-rays. An example of scientific measurement is time-resolved measurement such as CT (Computed Tomography) using TOF (Time Of Flight) technology.

[0029] The X-ray generating unit 2 has a target 24 that generates X-rays upon incidence of photoelectrons E emitted from the photoelectron generating unit 3. The photoelectron generating unit 3 has a photocathode 32 that emits photoelectrons E in response to the incidence of pulsed light L. Hereinafter, the direction in which the photocathode 32 and the target 24 face each other will be defined as the X direction, the direction perpendicular to the X direction (the depth direction of the paper in Figures 2 and 3) will be defined as the Y direction, and the direction perpendicular to the X and Y directions (the up and down direction of the paper in Figures 2 and 3) will be defined as the Z direction. The cylindrical portion 21 and valve portion 22 of the X-ray generating unit 2, which will be described later, and the light incidence window 31, cylindrical portion 33, cylindrical portion 34 and cylindrical member 36 of the photoelectron generating unit 3, which will be described later, constitute a vacuum enclosure that defines the internal space of the vacuum.

[0030] The X-ray generating unit 2 includes a cylindrical portion 21, a valve portion 22, an anode portion 23, and a target 24. The cylindrical portion 21 is formed in a cylindrical shape with a center line along the Z direction. The cylindrical portion 21 is made of, for example, metal. An X-ray emission window 25 is attached to one end 21a of the cylindrical portion 21 in the Z direction. The X-ray emission window 25 is made of, for example, a material made of a light element with high X-ray penetration ability, such as beryllium. The cylindrical portion 21 has a through hole 21c that penetrates the cylindrical portion 21 along the X direction. The through hole 21c is formed at a position facing the photocathode 32 in the X direction. The through hole 21c is formed in a cylindrical shape with a center line along the X direction.

[0031] The valve portion 22 is attached to the cylindrical portion 21 via an annular valve mounting fixture 26 so as to cover the other end 21b of the cylindrical portion 21 in the Z direction. The valve portion 22 is formed in a cylindrical shape, for example, having a center line along the Z direction. The valve portion 22 has a top portion 22a on the side opposite to the X-ray emission window 25 in the Z direction. The valve portion 22 is formed of, for example, glass.

[0032] The anode portion 23 is, for example, positioned inside the cylindrical portion 21 and the valve portion 22, and is formed in a cylindrical shape with a center line along the Z direction. The anode portion 23 is held at the top 22a of the valve portion 22 via an anode holder 27. A cylindrical portion 28 is attached to the end 23a of the anode portion 23 on the X-ray emission window 25 side. The cylindrical portion 28 is formed to surround the end 23a. The cylindrical portion 28 has a through hole 28a that penetrates the cylindrical portion 28 along the X direction. The through hole 28a is formed in a position facing the photocathode 32. Photoelectrons E emitted from the photocathode 32 pass through the through hole 28a and are incident on the target 24. The end 23a has an inclined surface 23b that is inclined with respect to the center line of the anode portion 23 so as to face the X-ray emission window 25 and the through hole 21c. The inclined surface 23b faces the photocathode 32 through the through hole 21c. The anode portion 23 is formed of, for example, metal. In operation, a positive voltage is applied to the anode portion 23.

[0033] The target 24 is provided on the inclined surface 23b. The target 24 faces the photocathode 32. The target 24 generates X-rays XL in response to the incidence of photoelectrons E emitted from the photocathode 32. In this example, the X-ray source 1 is a reflective X-ray source equipped with a reflective target 24 that outputs X-rays XL in the reflection direction, but it may also be a transmission X-ray source equipped with a transmission target that outputs X-rays XL in the transmission direction. The X-rays XL generated in the target 24 travel toward the X-ray emission window 25. The target 24 is made of a heavy metal with a large atomic number, such as tungsten. The target 24 is in contact with the anode portion 23, and the potential of the target 24 is equal to the potential of the anode portion 23.

[0034] The photoelectron generation unit 3 comprises a light incidence window 31, a photocathode 32, a cylindrical portion 33, a cylindrical portion 34, a control electrode portion 35, and a cylindrical member 36. The light incidence window 31 is positioned to face the target 24 in the X direction. The light incidence window 31 is formed, for example, in the shape of a disc with its thickness in the X direction. The light incidence window 31 has a surface 31a facing the target 24. The surface 31a is curved so as to be concave toward the opposite side of the target 24. The surface 31a is curved so as to be concave toward the opposite side of the focusing electrode 40, which will be described later. The light incidence window 31 is made of a light-transmitting material (for example, glass). Hereinafter, in the X direction, the side on which the target 24 is located relative to the light incidence window 31 (right side in Figure 3) will be referred to as the first side S1, and the side opposite to the first side S1 (left side in Figure 3) will be referred to as the second side S2.

[0035] The photocathode 32 is formed on the surface 31a of the light incident window 31. The photocathode 32 is curved along the surface 31a. That is, the photocathode 32 is curved so as to be concave toward the opposite side (second side S2) from the focusing electrode 40 described later. The photocathode 32 emits photoelectrons E in response to the incidence of pulsed light L output from the light source 4 described later. Specifically, pulsed light L that enters the light incident window 31 from the second side S2 and passes through the light incident window 31 is incident on the photocathode 32, and the photocathode 32 emits pulsed photoelectrons E toward the first side S1 in response to the incidence of the pulsed light L. The pulsed light L enters the light incident portion 31b of the light incident window 31. The photocathode 32 emits photoelectrons E from the portion that overlaps with the light incident portion 31b of the light incident window 31. As an example, the photocathode 32 emits photoelectrons E from a photoelectron emission point Q. The photocathode 32 is electrically connected to a connection part 37, which will be described later. In operation, a negative voltage is applied to the photocathode 32, for example, via the connection part 37. The photocathode 32 is, for example, a Na-K bialkali photocathode. The photocathode 32 may be formed from a cesium-free material. In this case, the durability of the photocathode 32 against ion collisions (ion feedback) of ions generated at the target 24 when photoelectrons E are incident and emitted from the target 24 toward the photocathode 32 can be improved.

[0036] The cylindrical portions 33 and 34 are arranged in this order along the X direction on the first side S1 of the light incidence window 31. The cylindrical portions 33 and 34 are formed of an insulating material (e.g., glass) and have the same diameter. Between the light incidence window 31 and the cylindrical portion 33, substantially annular connecting portions 37 and 38, made of, for example, metal, are arranged in this order toward the first side S1. The connecting portion 37 is electrically connected to the photocathode 32. A part of the connecting portion 42 of the focusing electrode 40, which will be described later, is located between the cylindrical portion 33 and the cylindrical portion 34.

[0037] The control electrode section 35 is positioned between the photocathode 32 and the target 24 in the X direction. The control electrode section 35 is positioned inside the cylindrical section 33 and the cylindrical section 34. The control electrode section 35 has a focusing electrode 40 and an accelerating electrode 50.

[0038] The focusing electrode 40 is positioned to face the photocathode 32 in the X direction. The focusing electrode 40 forms an electric field for focusing the photoelectrons E emitted from the photocathode 32. The focusing electrode 40 is made of, for example, a metal.

[0039] The focusing electrode 40 has a cylindrical portion 41 and a connecting portion 42. The cylindrical portion 41 is formed in a cylindrical shape with a center line along the X direction (the direction in which the focusing electrode 40 faces the photocathode 32). In operation, a negative voltage is applied to the cylindrical portion 41 of the focusing electrode 40, for example, via the connecting portion 42.

[0040] The cylindrical portion 41 has a cylindrical portion 43, a curved portion 44, and a flange portion 45. The cylindrical portion 43 is formed in a cylindrical shape with a center line along the X direction. The curved portion 44 is formed at the end of the second side S2 of the cylindrical portion 43 and is curved in a dome shape so as to be convex toward the photocathode 32.

[0041] The curved portion 44 has a surface 44a facing the photoelectric surface 32 and a surface 44b (first curved surface) on the side opposite to the surface 44a. The surface 44a is curved so as to be convex toward the photoelectric surface 32 and is curved along the photoelectric surface 32. The surface 44b faces the acceleration electrode 50 disposed inside the cylindrical portion 41. The surface 44b is curved so as to be recessed toward the side opposite to the acceleration electrode 50 (second side S2). In this example, the surface 44b is curved along the surface 44a. The surface 44b constitutes a part of the surface 40a of the focusing electrode 40 that faces the acceleration electrode 50. That is, the surface 40a has the surface 44b.

[0042] The curved portion 44 has a through hole 44c penetrating through the end portion of the second side S2 of the curved portion 44 along the X direction. The through hole 44c is a through hole (photoelectron passage hole) for the photoelectrons E emitted from the photoelectric surface 32 to pass through. The through hole 44c is formed at a position overlapping with the light incident portion 31b of the light incident window 31 when viewed from the X direction in the curved portion 44. The through hole 44c is formed, for example, in a circular shape when viewed from the X direction. The flange portion 45 is formed, for example, in an annular plate shape and is formed so as to extend outward from the end portion of the first side S1 of the cylindrical portion 43.

[0043] The connecting portion 42 is formed, for example, in an annular shape when viewed from the X direction and is connected to the cylindrical portion 41 in the flange portion 45. The potential of the connecting portion 42 is equal to the potential of the cylindrical portion 41. The connecting portion 42 is drawn out to the outside from between the cylindrical portion 33 and the cylindrical portion 34.

[0044] The acceleration electrode 50 is disposed between the focusing electrode 40 and the target 24. That is, when the direction in which the photoelectrons E emitted from the photoelectric surface 32 travel toward the target 24 is taken as the traveling direction of the photoelectrons E, the acceleration electrode 50 is disposed at the rear stage in the traveling direction of the photoelectrons E with respect to the focusing electrode 40. In other words, the focusing electrode 40 and the acceleration electrode 50 are disposed such that the photoelectrons E emitted from the photoelectric surface 32 pass through the through hole 44c, which is the electron passage hole of the focusing electrode 40, and the through hole 54c (described later), which is the electron passage hole of the acceleration electrode 50, in this order.

[0045] In this example, the acceleration electrode 50 is arranged so as to overlap a part of the focusing electrode 40 in a direction perpendicular to the X direction (the direction in which the focusing electrode 40 faces the photocathode 32). Specifically, the first cylindrical portion 53 of the acceleration electrode 50 described later overlaps a part of the cylindrical portion 43 and the curved portion 44 of the focusing electrode 40. In the present embodiment, the acceleration electrode 50 is arranged inside the cylindrical portion 41 of the focusing electrode 40.

[0046] The acceleration electrode 50 forms an electric field for accelerating the photoelectrons E emitted from the photocathode 32 and passing through the through-hole 44c of the focusing electrode 40. The acceleration electrode 50 is formed of, for example, metal. The acceleration electrode 50 has a cylindrical portion 51 and a connecting portion 52. The cylindrical portion 51 is formed in a cylindrical shape having a center line along the X direction. In this example, the center line of the cylindrical portion 51 coincides with the center line of the cylindrical portion 41 of the focusing electrode 40. The cylindrical portion 51 of the acceleration electrode 50 is grounded via the connecting portion 52, for example, in the operating state.

[0047] The cylindrical portion 51 has a first cylindrical portion 53, a bottom plate portion 54, a first flange portion 55, a second cylindrical portion 56, and a second flange portion 57. The first cylindrical portion 53 is formed in a cylindrical shape having a center line along the X direction. The bottom plate portion 54 is formed at the end of the second side S2 of the first cylindrical portion 53. The bottom plate portion 54 is formed, for example, in a disk shape having a center line along the X direction. The bottom plate portion 54 is arranged so as to overlap a part of the curved portion 44 of the focusing electrode 40 in a direction perpendicular to the X direction.

[0048] The bottom plate portion 54 has a surface 54a facing the surface 44b of the curved portion 44 of the focusing electrode 40 and a surface 54b on the opposite side of the surface 54a. The surface 54a has a central region R1 and a curved region R2 (second curved surface). The central region R1 is formed in a planar shape along a plane perpendicular to the X direction. The curved region R2 surrounds the central region R1 and is curved so as to be convex toward the surface 44b of the focusing electrode 40. The surface 54b is formed, for example, in a planar shape along a plane perpendicular to the X direction.

[0049] The base plate portion 54 has a through hole 54c that penetrates the base plate portion 54 along the X direction. The through hole 54c is a through hole (photoelectron passage hole) through which photoelectrons E that have passed through the through hole 44c of the focusing electrode 40 can pass. The through hole 54c is formed in the base plate portion 54 at a position that overlaps with the focusing electrode 40 when viewed from the X direction. The through hole 54c is formed in a cylindrical shape, for example, with a center line along the X direction. The diameter of the through hole 54c is, for example, smaller than the diameter of the through hole 44c of the focusing electrode 40.

[0050] The first flange portion 55 is formed, for example, in the shape of an annular plate and is formed to extend outward from the end of the first side S1 of the first cylindrical portion 53. The second cylindrical portion 56 extends upward from the outer end of the first flange portion 55 toward the first side S1. The second flange portion 57 is formed, for example, in the shape of an annular plate and is formed to protrude outward from the end of the first side S1 of the second cylindrical portion 56.

[0051] The space P1 inside the cylindrical portion 51 of the accelerating electrode 50 has a first space P11 and a second space P12. The first space P11 is, for example, a space defined by a through hole 54c. The first space P11 is located on the side of the focusing electrode 40 (second side S2) in space P1. The first space P11 is formed in a cylindrical shape, for example, having a center line along the X direction. The second space P12 is, for example, a space defined by the inner surfaces of the first cylindrical portion 53 and the second cylindrical portion 56 of the cylindrical portion 51. The second space P12 is located on the side of the target (first side S1) in space P1. The second space P12 is formed in a cylindrical shape, for example, having a center line along the X direction. The second space P12 has a larger diameter than the first space P11.

[0052] The connecting portion 52 is formed in an annular shape when viewed, for example, from the X direction, and is connected to the cylindrical portion 51 at the second flange portion 57. The potential of the connecting portion 52 is equal to the potential of the cylindrical portion 51. The connecting portion 52 is led out to the outside from the first side S1 of the cylindrical portion 34.

[0053] The cylindrical member 36 is positioned between the accelerating electrode 50 and the target 24 in the X direction. The cylindrical member 36 is formed in a cylindrical shape with a center line along the X direction. The cylindrical member 36 extends from the through hole 21c of the cylindrical portion 21 toward the photocathode 32 along the X direction, and the end of the second side S2 of the cylindrical member 36 is positioned to face the first flange portion 55 of the accelerating electrode 50. The cylindrical member 36 is formed of, for example, metal.

[0054] The cylindrical member 36 has a main body portion 81 and an insertion portion 82. The end portion 81a of the second side S2 of the main body portion 81 is positioned inside the second cylindrical portion 56 of the accelerating electrode 50. An annular connecting portion 83 is attached to the end portion 81a. The cylindrical member 36 is connected to the connecting portion 52 of the accelerating electrode 50 via the connecting portion 83, and the potential of the cylindrical member 36 is equal to the potential of the accelerating electrode 50.

[0055] The insertion portion 82 is formed at the end of the first side S1 of the main body portion 81. The diameter of the insertion portion 82 is smaller than the diameter of the main body portion 81. The insertion portion 82 is inserted into the through hole 21c of the cylindrical portion 21 of the X-ray generating unit 2. The outer surface of the insertion portion 82 is in contact with the inner surface of the through hole 21c, and the potential of the cylindrical member 36 is equal to the potential of the cylindrical portion 21. That is, since the cylindrical member 36 is in contact with both the accelerating electrode 50 and the cylindrical portion 21, the potentials of the accelerating electrode 50, the cylindrical member 36, and the cylindrical portion 21 are equal. A through hole 82a is formed at the end of the first side S1 of the insertion portion 82, extending through in the X direction.

[0056] The cylindrical member 36 has the same potential throughout. The cylindrical member 36 defines an equipotential space P2 (drift space) through which photoelectrons E pass. The equipotential space P2 is a space defined by the main body 81 and the insertion part 82. In this embodiment, the equipotential space is not necessarily limited to a space that is perfectly equipotential, but may be a space that has a potential state that has almost no potential effect on the passing photoelectrons E.

[0057] The light source 4 outputs pulsed light L, which is pulsed light, toward the photocathode. The light source 4 is, for example, a laser diode. The light source 4 emits pulsed light L at a predetermined timing, for example, a predetermined period, based on the control of the control unit 5. The control unit 5 is composed of, for example, a computer including a CPU, RAM, ROM, etc. The control unit 5 controls the operation of the light source 4.

[0058] Next, the operation of the X-ray source 1 will be described. In operation, voltages are applied to the photocathode 32, the focusing electrode 40, and the anode section 23. The accelerating electrode 50 and the cylindrical member 36 are grounded. For example, a voltage of -2.5kV is applied to the photocathode 32, a voltage of -3kV is applied to the focusing electrode 40, and a voltage of 120kV is applied to the anode section 23. Since the accelerating electrode 50 and the cylindrical member 36 are grounded, their potentials are 0kV. In other words, with the accelerating electrode 50 and the cylindrical member 36 as the ground potential (reference potential), a negative potential is applied to the photocathode 32 and the focusing electrode 40, and a positive potential is applied to the anode section 23. In operation, first, pulsed light L is output from the light source 4 toward the light incident window 31. When the pulsed light L passes through the light incident window 31 and enters the photocathode 32, photoelectrons E are emitted from the photocathode 32 toward the target 24. These photoelectrons E form a pulsed electron beam. These photoelectrons E are accelerated toward the target 24 by the accelerating electrode 50. Specifically, first, the photoelectrons E are accelerated by the potential difference (2.5 kV in this example) between the photocathode 32 and the accelerating electrode 50.

[0059] In the X-ray source 1, a focusing electrode 40 is positioned between the photocathode 32 and the accelerating electrode 50. As a result, the photoelectrons E are accelerated by the accelerating electrode 50 and focused by the focusing electrode 40. Therefore, it is possible to focus the photoelectrons E, which have relatively low energy before being accelerated by the accelerating electrode 50, and thus achieve good focusing of the photoelectrons E.

[0060] Photoelectrons E that have passed through the accelerating electrode 50 pass through the equipotential space P2 inside the cylindrical member 36. Since the cylindrical member 36 is at an equipotential, the photoelectrons E are not accelerated while passing through the cylindrical member 36. After passing through the cylindrical member 36, the photoelectrons E are accelerated toward the target 24. Specifically, the photoelectrons E are accelerated by the potential difference between the cylindrical member 36 and the target 24 (120 kV in this example). Subsequently, the photoelectrons E are incident on the target 24. The target 24 generates pulsed X-rays XL upon the incidence of photoelectrons E. The X-rays XL generated in the target 24 pass through the X-ray emission window 25 and are emitted outside the X-ray source 1. [Operation and Effects]

[0061] In the X-ray source 1, the focusing electrode 40 is positioned facing the photocathode 32, and the accelerating electrode 50 is positioned between the focusing electrode 40 and the target 24. That is, the accelerating electrode 50 is positioned behind the focusing electrode 40 in the direction of photoelectron E propagation. This allows for the focusing of relatively low-energy photoelectrons E before they are accelerated by the accelerating electrode 50, resulting in good focusing of the photoelectrons E.

[0062] Here, as shown in Figure 4(a), the photoelectrons E emitted from the photocathode 32 are accelerated and their energy increases as they approach the accelerating electrode 50. Figure 4(a) shows multiple equipotential surfaces ES. The size of the circles of photoelectrons E in the figure indicates the energy of the photoelectrons E, showing that they are accelerated from left to right, and the energy of the photoelectrons E gradually increases. As shown in Figure 4(b), when photoelectrons E1, E2, and E3 are bent by the focusing electrode, the photoelectron E1 with the lowest energy is the easiest to bend, and the photoelectron E3 with the highest energy is the most difficult to bend. Therefore, high-energy photoelectrons E are more difficult to focus than low-energy photoelectrons E, and to focus the photoelectrons E to the same extent, it is necessary to apply a high voltage to the focusing electrode to form a strong electric field (electrostatic lens). Alternatively, if the voltage applied to the focusing electrode is the same, high-energy photoelectrons E are more difficult to focus to a smaller size (microfocusing) than low-energy photoelectrons E.

[0063] Thus, when the accelerating electrode is positioned between the photocathode and the focusing electrode, a high voltage must be applied to the focusing electrode to focus high-energy photoelectrons accelerated by the accelerating electrode. Alternatively, if high-energy photoelectrons E are focused with the same voltage, the focal length becomes long, which may result in a larger device or a larger focal diameter (making microfocusing difficult). On the other hand, in the X-ray source 1 according to this embodiment, the accelerating electrode 50 is positioned downstream of the focusing electrode 40 in the direction of photoelectron E propagation, and relatively low-energy photoelectrons E before being accelerated by the accelerating electrode 50 can be focused, so the voltage applied to the focusing electrode 40 can be reduced, or the photoelectrons E can be focused to a microfocus.

[0064] The accelerating electrode 50 is positioned so as to overlap a portion of the focusing electrode 40 in a direction perpendicular to the direction in which the focusing electrode 40 faces the photocathode 32. This allows the accelerating electrode 50 to be brought closer to the focusing electrode 40, thereby enabling efficient acceleration of photoelectrons E.

[0065] The focusing electrode 40 has a cylindrical portion 41 with a center line aligned in the direction facing the photocathode 32, and the accelerating electrode 50 is positioned inside the cylindrical portion 41 of the focusing electrode 40. This allows the accelerating electrode to be brought closer to the focusing electrode, enabling good acceleration of photoelectrons.

[0066] The accelerating electrode 50 has a cylindrical portion 51 having a center line aligned with the direction in which the focusing electrode 40 faces the photocathode 32. This makes it possible to make the electric field formed by the accelerating electrode 50 more uniform compared to, for example, the case where the accelerating electrode 50 is formed by a flat mesh electrode, and to suppress unevenness in the trajectory of photoelectrons E. In addition, since the photoelectrons E do not collide with the mesh electrode and disappear, the loss of photoelectrons E can be suppressed.

[0067] Figure 5 is a diagram illustrating the trajectory of photoelectrons E when photoelectrons E emitted from the photocathode 132 are accelerated using a mesh electrode A. Figure 5(a) shows a plurality of equipotential surfaces ES. As an example of the trajectory of photoelectrons E, the trajectories of photoelectrons E4 to E7 are shown in the figure. As shown in Figure 5(a), the equipotential surfaces ES may become distorted in a wave-like manner as they approach the mesh electrode A. In this case, the trajectory of the photoelectrons E may not be affected by the distortion of the equipotential surfaces ES, as in the case of photoelectrons E4 and E5, while in the case of photoelectron E6, it may bend due to the distortion of the equipotential surfaces ES. Therefore, as shown in Figure 5(b), the trajectory of the photoelectrons E may become uneven, making it difficult to focus the photoelectrons E to a single point. Also, as in the case of photoelectron E7 shown in Figure 5(a), there is a risk that the photoelectron E may collide with the mesh electrode A and disappear. In contrast, in this embodiment, the accelerating electrode 50 has a cylindrical portion 51. In other words, the photoelectron passage hole (through hole 54c of the accelerating electrode 50) is composed of a single through hole provided in the electrode, and the photoelectron passage hole is not composed of a grid-like member or mesh-like member such as a mesh electrode. Therefore, as described above, it is possible to suppress unevenness in the trajectory of photoelectrons E and suppress the loss of photoelectrons E.

[0068] The surface 40a of the focusing electrode 40 has a curved surface 44b (first curved surface) that is concave toward the opposite side from the accelerating electrode 50, and the cylindrical portion 51 of the accelerating electrode 50 has a curved region R2 (second curved surface) that is convex toward the surface 44b of the focusing electrode 40. This makes it possible to suppress the generation of discharge between the focusing electrode 40 and the accelerating electrode 50.

[0069] The photocathode 32 is curved so as to be concave toward the opposite side of the focusing electrode 40. This allows photoelectrons E to be emitted in a state that facilitates good focusing.

[0070] The surface 44a of the focusing electrode 40 that faces the photocathode 32 in the curved portion 44 is curved to follow the photocathode 32. This allows for even better focusing of the photoelectrons E emitted from the photocathode.

[0071] In the accelerating electrode 50, the second space P12 inside the through hole 54c has a larger diameter than the first space P11 inside the cylindrical portion 51. The formation of this second space P12 prevents photoelectrons E traveling through the space P1 (internal space) inside the cylindrical portion 51 from coming into contact with the wall surface of the cylindrical portion 51.

[0072] The cylindrical member 36 has a uniform potential throughout and defines an equipotential space P2 through which photoelectrons E pass. This makes it possible to provide an equipotential space P2 that can be used, for example, to deflect the direction of propagation of photoelectrons E emitted from the photocathode 32 toward the target 24, or ions I generated in the target 24 when photoelectrons E are incident and moving from the target 24 toward the photocathode 32. For example, the direction of propagation of the photoelectrons E or ions I can be deflected in the equipotential space P2, thereby suppressing damage to the photocathode due to collisions with the ions I. The deflection of photoelectrons E will be described later. Furthermore, since the electron orbitals of the first side S1 and the second side S2 in the equipotential space P2 can be designed independently, the characteristics of the electron orbitals can be easily optimized. [First Modified Example]

[0073] The first modified X-ray source 1A will be described with reference to Figures 6 to 9. The first modified X-ray source 1A shown in Figure 6 differs from the X-ray source 1 according to the embodiment in that the shape of the cylindrical portion 41 of the focusing electrode 40 is different, the shape of the cylindrical portion 51 of the accelerating electrode 50 is different, and a deflector 6 is further provided.

[0074] In the first modified example, the cylindrical portion 41 of the focusing electrode 40 has a cylindrical portion 43A, an inclined portion 44A, and a flange portion 45. The cylindrical portion 43A and the inclined portion 44A will be described in detail below. The flange portion 45 has the same configuration as the flange portion 45 in the embodiment, so its description will be omitted.

[0075] The cylindrical portion 43A is formed in a cylindrical shape with a center line along the X direction (the direction in which the focusing electrode 40 faces the photocathode 32). The cylindrical portion 43A has a pair of first ventilation holes 43a that penetrate the cylindrical portion 43A along the Z direction. The pair of first ventilation holes 43a are formed, for example, on both sides of the cylindrical portion 43A in the Z direction, with the center line of the cylindrical portion 43A in between. The first ventilation holes 43a are formed in a circular shape when viewed from the Z direction, for example.

[0076] The inclined portion 44A is formed at the end of the second side S2 of the cylindrical portion 43A. The inclined portion 44A has a surface 44a facing the photocathode 32 and a surface 44b (first inclined surface) opposite to surface 44a. Surface 44a has an inclined surface that is inclined so as it approaches the accelerating electrode 50 it moves away from the center line of the focusing electrode 40. Surface 44b faces the accelerating electrode 50. Surface 44b is inclined so as it approaches the accelerating electrode 50 it moves away from the center line of the focusing electrode 40. Surface 44b is formed in an annular shape that surrounds the through hole 44c described later when viewed from the X direction, for example. Surface 44b constitutes a part of the surface 40a of the focusing electrode 40 that faces the accelerating electrode 50. That is, surface 40a has surface 44b.

[0077] The inclined portion 44A has a through hole 44c that penetrates the end of the second side S2 of the inclined portion 44A along the X direction. The through hole 44c is formed in the inclined portion 44A at a position that overlaps with the light incident portion 31b of the light incident window 31 when viewed from the X direction. The through hole 44c is formed in a cylindrical shape, for example, having a center line along the X direction.

[0078] In the first modified example, the cylindrical portion 51 of the accelerating electrode 50 has a first cylindrical portion 53A, an inclined portion 54A, a first flange portion 55, a second cylindrical portion 56, and a second flange portion 57. The first cylindrical portion 53A and the inclined portion 54A will be described in detail below. The first flange portion 55, the second cylindrical portion 56, and the second flange portion 57 have the same configuration as the first flange portion 55, the second cylindrical portion 56, and the second flange portion 57 in the embodiment, respectively, so their description will be omitted.

[0079] The first cylindrical portion 53A is formed in a cylindrical shape having a center line along the X direction. The first cylindrical portion 53A has a cylindrical portion 53A1 formed on the first side S1 and a cylindrical portion 53A2 formed on the second side S2. The outer diameter of the cylindrical portion 53A2 is, for example, equal to the outer diameter of the cylindrical portion 53A1. The inner diameter of the cylindrical portion 53A2 is, for example, smaller than the inner diameter of the cylindrical portion 53A1. That is, the thickness of the cylindrical portion 53A2 is larger than the thickness of the cylindrical portion 53A1.

[0080] The first cylindrical portion 53A has a pair of second ventilation holes 53a that penetrate the first cylindrical portion 53A along the Z direction. The pair of second ventilation holes 53a are formed, for example, on both sides of the first cylindrical portion 53A in the Z direction, with the center line of the first cylindrical portion 53A in between. The second ventilation holes 53a are formed in a circular shape when viewed from the Z direction. The second ventilation holes 53a are formed in a position that overlaps with the first ventilation holes 43a of the focusing electrode 40 when viewed from the Z direction. The diameter of the second ventilation holes 53a is smaller than the diameter of the first ventilation holes 43a of the focusing electrode 40.

[0081] The space P1 inside the cylindrical portion 51 of the accelerating electrode 50 is connected to the space P3 outside the cylindrical portion 41 of the focusing electrode 40 via the first ventilation hole 43a and the second ventilation hole 53a. The space P3 is, for example, the space formed between the inner surface of the cylindrical portion 33 and the outer surface of the cylindrical portion 43 of the cylindrical portion 41.

[0082] The inclined portion 54A is formed at the end of the second side S2 of the first cylindrical portion 53A (i.e., the end of the second side S2 of the cylindrical portion 53A2). The inclined portion 54A has a surface 54a (second inclined surface) that faces the surface 44b of the inclined portion 44A of the focusing electrode 40, and a surface 54b opposite to surface 54a. Surface 54a is inclined so that it moves away from the center line of the focusing electrode 40 as it moves away from the focusing electrode 40. Surface 54a faces the surface 44b of the inclined portion 44A of the focusing electrode 40. Surface 54a is formed in an annular shape that surrounds the through hole 54c described later when viewed from the X direction, for example. Surface 54b is formed in a planar shape along a plane perpendicular to the X direction, for example.

[0083] The X-ray source 1A according to the first modified example further includes a deflector 6, as described above. The deflector 6 deflects the direction of propagation of photoelectrons E emitted from the photocathode 32 toward the target 24, or ions I (Figure 7(b)) generated in the target 24 when photoelectrons E are incident, and moving from the target 24 toward the photocathode 32, in the equipotential space P2. Ions I are, for example, positive ions generated when photoelectrons E are incident on the target 24. Ions I are, for example, positive ions produced when residual gas is attached to the target 24 and the residual gas is ionized by collision with photoelectrons E. If the deflector 6 is not provided, these positive ions may travel from the target 24 toward the photocathode 32 and collide with the photocathode 32, potentially damaging the photocathode 32 (ion feedback). By deflecting the direction of propagation of photoelectrons E or ions I with the deflector 6, such damage to the photocathode 32 can be suppressed.

[0084] The deflector 6 has, for example, a pair of deflection plates 84. In this example, the pair of deflection plates 84 are arranged inside the cylindrical member 36. The pair of deflection plates 84 are arranged to face each other in the Z direction. In this example, the pair of deflection plates 84 face each other in the Z direction with the center line of the cylindrical member 36 in between. The deflection plates 84 generate an electric field (deflection electric field) to deflect the direction of propagation of photoelectrons E or ions I. The deflection plates 84 are electrically connected to, for example, the control unit 5. The pair of deflection plates 84 generate an electric field between them by applying a voltage. The direction of propagation of photoelectrons E or ions I is deflected by the electric field as the photoelectrons E or ions I pass between the pair of deflection plates 84.

[0085] In this example, the control unit 5 controls the operation of the deflector 6 in addition to controlling the light source 4. During the first time period, from when photoelectrons E are emitted from the photocathode 32 due to the incidence of pulsed light L until the photoelectrons E are incident on the target 24, the control unit 5 does not perform any control to deflect the photoelectrons E. On the other hand, during the second time period T2, from when the photoelectrons E are incident on the target 24 until the next pulsed light L is incident on the photocathode 32, the control unit 5 controls the deflector 6 so that it deflects the direction of propagation of ions I. In other words, in this example, the deflector 6 deflects the direction of propagation of ions I, not the direction of propagation of photoelectrons E.

[0086] Figure 7 is a schematic diagram showing the trajectories of photoelectrons E and ions I in the first modified example. In the first time period T1, the control unit 5 does not apply a voltage to the pair of deflection plates 84 and does not generate an electric field between the pair of deflection plates 84. Therefore, in the first time period T1, the direction of propagation of photoelectrons E emitted from the photocathode 32 is not deflected by the deflection plates 84 (Figure 7(a)). On the other hand, in the second time period T2, the control unit 5 applies a voltage to the pair of deflection plates 84 and generates an electric field between the pair of deflection plates 84. As a result, the direction of propagation of ions I is deflected (Figure 7(b)).

[0087] For example, if the length of a pair of deflection plates 84 in the X direction is 30 mm, and the distance between the pair of deflection plates 84 in the direction in which they face each other is 10 mm, then by applying a voltage of 10 kV to the pair of deflection plates 84, the ions I at the exit of the deflection plates 84 can be bent by 1.8 mm in the Z direction.

[0088] In this way, by generating an electric field only during the second time period T2 when no photoelectrons E are emitted, the direction of propagation of ions I can be deflected. This allows, for example, ions I to collide with a part of the photocathode 32 other than the photoelectron emission point Q. Therefore, damage caused by collisions of ions I at the photoelectron emission point Q of the photocathode 32 can be suppressed. Here, even the lightest ion, the hydrogen ion, is heavier than the photoelectron E. For this reason, when photoelectrons E and hydrogen ions are accelerated with the same potential difference, the velocity difference between the two is about 40 times. Therefore, by generating an electric field only during the second time period T2, the slower-moving ions I can be effectively deflected.

[0089] In the first modification, as in the above embodiment, it is possible to focus relatively low-energy photoelectrons E before they are accelerated by the accelerating electrode 50, and to focus the photoelectrons E well. In the first modification, the surface 40a of the focusing electrode 40 has a surface 44b (first inclined surface) that is inclined so that it moves away from the center line of the focusing electrode 40 as it approaches the accelerating electrode 50, and the inclined portion 54A of the cylindrical portion 51 of the accelerating electrode 50 is arranged to face the surface 44b of the inclined portion 44A of the focusing electrode 40 and has a surface 54a (second inclined surface) that is inclined so that it moves away from the center line of the accelerating electrode 50 as it moves away from the focusing electrode 40. As a result, as in the embodiment, it is possible to suppress the occurrence of discharge between the focusing electrode 40 and the accelerating electrode 50.

[0090] The space P1 inside the cylindrical portion 51 of the accelerating electrode 50 is connected to the space P3 outside the cylindrical portion 41 of the focusing electrode 40 via the first ventilation hole 43a and the second ventilation hole 53a. This allows for effective vacuuming of the inside of the X-ray source. For example, when removing gas such as air from inside the X-ray source 1A to create a vacuum inside the X-ray source 1A, it is possible to suppress the residual gas in the space P1 inside the accelerating electrode 50.

[0091] The X-ray source 1A is equipped with a deflector 6 that deflects the direction of propagation of photoelectrons E emitted from the photocathode 32 toward the target 24, or ions I generated in the target 24 when photoelectrons E are incident, toward the photocathode 32 from the target 24, in an equipotential space P2. This makes it possible to suppress damage to the photocathode caused by collisions of ions I.

[0092] The deflector 6 has a pair of deflection plates 84 that generate an electric field to deflect the direction of propagation of photoelectrons E or ions I. The pair of deflection plates 84 are arranged to face each other in a direction perpendicular to the direction in which the focusing electrode 40 faces the photocathode 32 (Z direction). As a result, the direction of propagation of photoelectrons E or ions I can be deflected by the electric field generated by the pair of deflection plates 84.

[0093] The control unit 5 controls the deflector 6 so that it deflects the direction of ion I during the second time period T2, from when photoelectrons E are incident on the target 24 until the next pulse of light L is incident on the photocathode 32. In this case, when X-rays are generated using pulsed light L, damage to the photocathode 32 due to collisions of ion I can be suppressed.

[0094] In the example described above, the direction of propagation of ion I was deflected, but as shown in Figure 8, the direction of propagation of photoelectrons E may also be deflected. In this case, the control unit 5 applies a voltage to a pair of deflection plates 84 in the first time period T1, generating an electric field. This deflects the direction of propagation of photoelectrons E (Figure 8(a)). In this case, the photoelectrons E collide with the target 24 while bending. The target 24 is positioned offset in the Z direction from the photoelectron emission point Q of the photocathode 32 to the side where the photoelectrons E bend. Also, when deflecting the direction of propagation of ion I, the control unit 5 does not apply a voltage to the pair of deflection plates 84 in the second time period T2, and does not generate an electric field. Therefore, the direction of propagation of ion I is not deflected (Figure 8(b)).

[0095] In this way, by applying a voltage to the pair of deflection plates 84 only during the first time period, the direction of propagation of photoelectrons E can be deflected. In this case, since the target 24 is positioned offset in the Z direction from the photoelectron emission point Q of the photocathode 32, ions I traveling from the target 24 to the photocathode 32 can be made to collide with a part of the photocathode 32 other than the photoelectron emission point Q. Therefore, even in this case, damage caused by collisions of ions I at the photoelectron emission point Q of the photocathode 32 can be suppressed.

[0096] Furthermore, the potential difference between the accelerating electrode 50 and the photocathode 32 (approximately 3 kV in this example) is smaller than the potential difference between the target 24 and the photocathode 32 (approximately 120 kV in this example). Therefore, the kinetic energy of the photoelectrons E after acceleration by the accelerating electrode 50 (photoelectrons E after initial acceleration) is lower than the kinetic energy of the ions I emitted from the target 24. Consequently, the photoelectrons E after acceleration by the accelerating electrode 50 are easier to deflect than the ions I, making it easy to deflect the photoelectrons E. This allows, for example, to reduce the size of the pair of deflection plates 84. Alternatively, it allows to reduce the voltage (deflection voltage) applied to the pair of deflection plates 84. For example, when deflecting photoelectrons E accelerated with a potential difference of 3 kV and ions I accelerated with a potential difference of 120 kV, the same amount of displacement can be obtained by deflecting the photoelectrons E with 1 / 40th the deflection voltage compared to ions I.

[0097] As described above, the control unit 5 may control the deflector 6 so that in the first time period T1 the deflector 6 deflects the direction of travel of photoelectrons E or ions I. As a result, since photoelectrons accelerated by the accelerating electrode 50 are easier to deflect than ions I generated in the target 24, the photoelectrons can be easily deflected.

[0098] In the first modified example, the pair of deflection plates 84 were arranged parallel to each other. However, as shown in Figure 9, the pair of deflection plates 84 may be inclined with respect to the X direction (the direction in which the focusing electrode 40 faces the photocathode 32) so that they move away from each other as they approach the target 24. Even in this case, the electric field generated by the pair of deflection plates 84 can deflect the direction of propagation of photoelectrons or ions. Furthermore, it is possible to suppress the photoelectrons E from coming into contact with the deflection plates 84. That is, the closer the pair of deflection plates 84 are to the electron beam of the photoelectrons E, the more efficient they are at bending the photoelectrons E. However, if the pair of deflection plates 84 are brought too close to the electron beam of the photoelectrons E, the deflected electron beam may come into contact with the deflection plates 84, resulting in a loss of photoelectrons E reaching the target 24. In contrast, by inclining the pair of deflection plates 84 as shown in Figure 9, it is possible to suppress the photoelectrons E from coming into contact with the deflection plates and thus suppress the loss of photoelectrons E. [Second Modified Example]

[0099] Figure 10 shows an X-ray source 1B according to a second modification. The X-ray source 1B according to the second modification differs from the X-ray source 1A according to the first modification in that the deflector 6 does not have a pair of deflection plates 84, but has a pair of coil sections 85.

[0100] In this example, the pair of coil sections 85 are located on the outside of the cylindrical member 36. The pair of coil sections 85 are arranged to face each other in the Z direction (a direction perpendicular to the direction in which the focusing electrode 40 faces the photocathode 32). In this example, the pair of coil sections 85 face each other in the Z direction, with the cylindrical member 36 in between. The pair of coil sections 85 generate a magnetic field M (Figure 11) to deflect the direction of propagation of photoelectrons E or ions I. The pair of coil sections 85 generate a magnetic field M, for example, in the equipotential space P2 inside the cylindrical member 36 between the pair of coil sections 85. The direction of propagation of photoelectrons E or ions I is deflected by the magnetic field M as the photoelectrons E or ions I pass between the pair of coil sections 85.

[0101] As shown in Figure 11(a), each of the pair of coil sections 85 has a core member 85a and a coil wire 85b. The core member 85a is formed in a cylindrical shape, for example, having a center line along the Y direction (a direction perpendicular to the direction in which the focusing electrode 40 faces the photocathode 32). The coil wire 85b is wound around the core member 85a. Alternatively, the core members 85a of the pair of coil sections 85 may be formed in an annular shape, as shown in Figure 11(b). In this case, the magnetic field M can be applied uniformly to the periphery of the equipotential space P2 between the pair of coil sections 85. Or, the core member 85a may be composed of two semi-annular members divided at the position shown by the dashed line in Figure 11(b), and these may be arranged facing each other.

[0102] In the second modification, as in the above embodiment, relatively low-energy photoelectrons E before being accelerated by the accelerating electrode 50 can be focused, and the photoelectrons E can be focused well. In the second modification, the pair of coil sections 85 are arranged to face each other in the Z direction (a direction perpendicular to the direction in which the focusing electrode 40 faces the photocathode 32). As a result, the magnetic field M generated by the pair of coil sections 85 can deflect the direction of propagation of photoelectrons E or ions I. [Modification]

[0103] This disclosure is not limited to the embodiments and modifications described above. For example, the materials and shapes of each component are not limited to those described above, but can be made from a variety of materials and shapes.

[0104] The accelerating electrode 50 does not have to overlap with a part of the focusing electrode 40 in a direction perpendicular to the X direction (the direction in which the focusing electrode 40 faces the photocathode 32). For example, the entire accelerating electrode 50 may be positioned on the first side S1 relative to the focusing electrode 40. Thus, "the accelerating electrode is positioned between the focusing electrode and the target" includes cases where the focusing electrode 40 and the accelerating electrode 50 do not overlap, and cases where the focusing electrode 40 and the accelerating electrode 50 overlap. Furthermore, the entire focusing electrode 40 does not have to be positioned between the photocathode 32 and the accelerating electrode 50. It is sufficient if at least a part of the focusing electrode 40 is located between the photocathode 32 and the accelerating electrode 50. The accelerating electrode 50 does not have to have a cylindrical portion 51. For example, it may be flat or mesh-shaped.

[0105] The photocathode 32 does not have to be curved so as to be recessed toward the opposite side (second side S2) from the focusing electrode 40, but may be, for example, planar. The space P1 inside the cylindrical portion 51 of the accelerating electrode 50 does not have to have a second space P12 having a larger diameter than the first space P11, and the entire space P1 may have the same diameter. The cylindrical member 36 may have the same potential throughout and does not have to have the same potential as the accelerating electrode 50. The light source 4 does not have to output pulsed light, but may output continuous light, for example. In this case, X-rays XL are continuously generated at the target 24.

[0106] In the first modified example, the first ventilation holes 43a formed in the cylindrical portion 41 of the focusing electrode 40 do not have to be a pair; there may be only one or three or more. The first ventilation holes 43a may not be formed in the cylindrical portion 41. The second ventilation holes 53a formed in the cylindrical portion 51 of the accelerating electrode 50 do not have to be a pair; there may be only one or three or more. The second ventilation holes 53a may not be formed in the cylindrical portion 51.

[0107] In the first modified example, the pair of deflection plates 84 do not have to face each other in the Z direction, but they may face each other in the Y direction. Also, the deflection plates 84 do not have to be a pair, but a single deflection plate may be used. The X-ray source 1A in the first modified example does not have to be equipped with a deflector 6. In the second modified example, the pair of coil sections 85 do not have to face each other in the Z direction, but they may face each other in the Y direction. Also, the coil section 85 does not have to be a pair, but a single coil may be used. In that case, the single coil may extend to surround the area of ​​the cylindrical member 36 surrounded by the pair of coil sections 85. In the second modified example, the pair of coil sections 85 of the deflector 6 do not have to be located outside the cylindrical member 36, but they may be located inside the cylindrical member 36. In this case, compared to the case where the pair of coil sections 85 are located outside the cylindrical member 36, the pair of coil sections 85 can be brought closer to the trajectory of the photoelectrons E, so the current flowing through the coil sections 85 can be reduced. The X-ray source 1B in the second modified example does not need to be equipped with a deflector 6. The light source 4 only needs to emit pulsed light L at predetermined timings and does not necessarily need to emit pulsed light L periodically.

[0108] 1, 1A, 1B...X-ray source, 4...light source, 5...control unit, 6...deflector, 41, 51...cylindrical part, 24...target, 32...photocathode, 35...control electrode part, 36...cylindrical member, 40...focusing electrode, 40a...surface, 43a...first ventilation hole, 44a...surface, 44b...surface (first curved surface, first inclined surface), 50...accelerating electrode, 53a...second ventilation hole, 54a...surface (second curved surface, second inclined surface), 84...deflecting plate, 85...coil part, E...photoelectron, I...ion, L...pulsed light (light), P1...space, P11...first space, P12...second space, P2...equipotential space, P3...space, T1...first time zone, T2...second time zone, XL...X-ray.

Claims

1. An X-ray source comprising: a photocathode that emits photoelectrons in response to incident light; a target that generates X-rays in response to the incident photoelectrons emitted from the photocathode; and a control electrode section disposed between the photocathode and the target, wherein the control electrode section comprises: a focusing electrode disposed facing the photocathode and focusing the photoelectrons emitted from the photocathode; and an accelerating electrode disposed between the focusing electrode and the target and accelerating the photoelectrons.

2. The X-ray source according to claim 1, wherein the accelerating electrode is arranged such that it overlaps with a portion of the focusing electrode in a direction perpendicular to the direction in which the focusing electrode faces the photocathode.

3. The X-ray source according to claim 1 or 2, wherein the focusing electrode has a cylindrical portion having a center line aligned in the direction in which the focusing electrode faces the photocathode, and the accelerating electrode is disposed inside the cylindrical portion of the focusing electrode.

4. The X-ray source according to any one of claims 1 to 3, wherein the accelerating electrode has a cylindrical portion having a center line aligned with the direction in which the focusing electrode faces the photocathode.

5. The X-ray source according to claim 4, wherein the surface of the focusing electrode facing the accelerating electrode has a first curved surface that curves inward toward the opposite side of the accelerating electrode, and the cylindrical portion of the accelerating electrode is arranged to face the first curved surface and has a second curved surface that curves outward toward the first curved surface.

6. The X-ray source according to claim 4, wherein the surface of the focusing electrode facing the accelerating electrode has a first inclined surface that is inclined so as it approaches the accelerating electrode it moves away from the center line of the focusing electrode, and the cylindrical portion of the accelerating electrode is arranged to face the first inclined surface and has a second inclined surface that is inclined so as it moves away from the focusing electrode it moves away from the center line of the accelerating electrode.

7. The X-ray source according to any one of claims 1 to 6, wherein the photocathode is curved so as to be concave toward the opposite side from the focusing electrode.

8. The X-ray source according to claim 7, wherein the surface of the focusing electrode facing the photocathode is curved to follow the photocathode.

9. The X-ray source according to claim 4, wherein the space inside the cylindrical portion of the accelerating electrode comprises a cylindrical first space located on the side of the focusing electrode and a second space located on the target side relative to the first space and having a larger diameter than the first space.

10. The X-ray source according to claim 3, wherein the accelerating electrode has a cylindrical portion having a center line aligned with the direction in which the focusing electrode faces the photocathode, a first ventilation hole is formed in the cylindrical portion of the focusing electrode, a second ventilation hole is formed in the cylindrical portion of the accelerating electrode, and the space inside the cylindrical portion of the accelerating electrode is connected to the space outside the cylindrical portion of the focusing electrode via the first and second ventilation holes.

11. An X-ray source according to any one of claims 1 to 10, wherein a cylindrical metal member having a center line aligned with the direction in which the focusing electrode faces the photocathode is disposed between the accelerating electrode and the target, the cylindrical member having the same potential throughout and defining an equipotential space within which the photoelectrons pass.

12. The X-ray source according to claim 11, further comprising a deflector that deflects the direction of propagation of photoelectrons emitted from the photocathode toward the target, or ions generated in the target when photoelectrons are incident, toward the photocathode, in the equipotential space.

13. The X-ray source according to claim 12, wherein the deflector comprises either a deflection plate that generates an electric field for deflecting the direction of propagation of the photoelectrons or ions, or a coil that generates a magnetic field for deflecting the direction of propagation of the photoelectrons or ions.

14. The X-ray source according to claim 13, wherein the deflector has a pair of deflection plates, the pair of deflection plates are arranged to face each other in a direction perpendicular to the direction in which the focusing electrode faces the photocathode.

15. The X-ray source according to claim 14, wherein the pair of deflection plates are arranged at an inclination with respect to the direction in which the focusing electrode faces the photocathode, such that they move away from each other as they move toward the target.

16. The X-ray source according to claim 13, wherein the deflector has a pair of coil portions, and the pair of coil portions are arranged to face each other in a direction perpendicular to the direction in which the focusing electrode faces the photocathode.

17. The X-ray source according to claim 12, further comprising: a light source that outputs pulsed light toward the photocathode at a predetermined timing; and a control unit that controls the light source and the deflector, wherein the control unit controls the deflector so that the deflector deflects the direction of propagation of the photoelectrons or ions during either a first time period from when the photoelectrons are emitted from the photocathode due to the incidence of the pulsed light until the photoelectrons are incident on the target, or a second time period from when the photoelectrons are incident on the target until the next pulsed light is incident on the photocathode.

18. The X-ray source according to claim 17, wherein the control unit controls the deflector such that the deflector deflects the direction of propagation of the photoelectrons during the first time period.

Images