X-ray source

Abstract

The X-ray source includes a photocathode 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 photocathode, and a control electrode unit arranged between the photocathode and the target. The control electrode unit has a focusing electrode arranged to face the photocathode and that focuses the photoelectrons emitted from the photocathode, and an accelerating electrode arranged between the focusing electrode and the target and that accelerates the photoelectrons.

Description

[Technical Field]

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

[0002] Patent Document 1 describes an X-ray generating tube (X-ray source) that includes a photoelectron emitting layer, an acceleration mesh arranged parallel to the photoelectron emitting layer, and a cylindrical focusing electrode arranged downstream of the acceleration mesh (FIG. 5). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 60-47355 Summary of the Invention [Problem to be solved by the invention]

[0004] The X-ray source described above may be required to have, for example, a fine focus to reduce the focal spot size of the output X-rays, and may be required to focus the photoelectrons well.

[0005] An object of one aspect of the present disclosure is to provide an X-ray source that can effectively focus photoelectrons. [Means for solving the problem]

[0006] An X-ray source according to one aspect of the present disclosure is [1] "an X-ray source comprising: a photocathode that emits photoelectrons in response to 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 unit arranged between the photocathode and the target, wherein the control electrode unit has: a focusing electrode arranged to face the photocathode and focusing the photoelectrons emitted from the photocathode; and an accelerating electrode arranged between the focusing electrode and the target and accelerating the photoelectrons."

[0007] In this X-ray source, the focusing electrode is positioned opposite the photocathode, and the accelerating electrode is positioned between the focusing electrode and the target. In other words, the accelerating electrode is positioned after the focusing electrode in the direction of photoelectron propagation. This makes it possible to focus photoelectrons, which have relatively low energy before being accelerated by the accelerating electrode, and achieve good focusing of the photoelectrons.

[0008] An X-ray source according to one aspect of the present disclosure may be [2] "the X-ray source according to [1], wherein the accelerating 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 accelerating electrode can be brought close to the focusing electrode, and photoelectrons can be accelerated well.

[0009] An X-ray source according to one aspect of the present 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 a direction in which the focusing electrode faces the photocathode, and the accelerating electrode is disposed inside the cylindrical portion of the focusing electrode." In this case, the accelerating electrode can be brought close to the focusing electrode, and photoelectrons can be accelerated effectively.

[0010] An X-ray source according to one aspect of the present 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 along the direction in which the focusing electrode faces the photocathode." In this case, compared to when the accelerating electrode is formed of, for example, a flat mesh electrode, the electric field formed by the accelerating electrode can be made more uniform, and unevenness in the trajectories of photoelectrons can be suppressed. Furthermore, since photoelectrons do not collide with the mesh electrode and are annihilated, loss of photoelectrons can be suppressed.

[0011] An X-ray source according to one aspect of the present disclosure may be [5] "the X-ray source according to [4], wherein a surface of the focusing electrode facing the accelerating electrode has a first curved surface that is curved so as to be concave toward the side opposite to the accelerating electrode, and the cylindrical portion of the accelerating electrode has a second curved surface that is disposed facing the first curved surface and is curved so as to be convex toward the first curved surface." In this case, it is possible to suppress the occurrence of discharge between the focusing electrode and the accelerating electrode.

[0012] An X-ray source according to one aspect of the present disclosure may be [6] "the X-ray source according to [4], wherein a surface of the focusing electrode facing the accelerating electrode has a first inclined surface inclined so as 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 disposed opposite the first inclined surface and inclined so as to move away from the center line of the accelerating electrode as it moves away from the focusing electrode." In this case, it is possible to suppress the occurrence of discharge between the focusing electrode and the accelerating electrode.

[0013] The X-ray source according to one aspect of the present disclosure may be [7] "the X-ray source according to any one of [1] to [6], wherein the photocathode is curved so as to be recessed toward the opposite side from the focusing electrode." In this case, photoelectrons can be emitted in a state that makes it easy to focus them well.

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

[0015] An X-ray source according 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 has a cylindrical first space arranged on the focusing electrode side, and a second space arranged on the target side of the first space and having a larger diameter than the first space." In this case, the formation of the second space can prevent photoelectrons traveling through the internal space of the cylindrical portion from coming into contact with a wall surface of the cylindrical portion.

[0016] An X-ray source according to one aspect of the present disclosure may be

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

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

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

[10] , wherein a metallic cylindrical member having a center line along a 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 therein through which the photoelectrons pass." In this case, for example, an equipotential space can be provided that can be used to deflect the traveling direction of photoelectrons emitted from the photocathode and heading toward the target, or ions generated in the target when photoelectrons are incident and heading from the target toward the photocathode.

[0018] An X-ray source according to one aspect of the present disclosure may be

[12] "the X-ray source according to

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

[0019] An X-ray source according to one aspect of the present 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 traveling direction of the photoelectrons or the ions, or a coil unit that generates a magnetic field for deflecting the traveling direction of the photoelectrons or the ions." In this case, the electric field or the magnetic field can suppress damage to the photocathode due to ion collisions.

[0020] An X-ray source according 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 a direction in which the focusing electrode faces the photocathode." In this case, the traveling direction of photoelectrons or ions can be deflected by an electric field generated by the pair of deflection plates.

[0021] An X-ray source according to one aspect of the present disclosure may be

[15] "the X-ray source according to

[14] , in which the pair of deflection plates are arranged at an angle with respect to the direction in which the focusing electrodes face the photocathode so that they move away from each other toward the target." In this case, the traveling direction of photoelectrons or ions can be deflected by the electric field generated by the pair of deflection plates. Also, it is possible to prevent the deflected photoelectrons from coming into contact with the deflection plates.

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

[16] "the X-ray source according to

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

[0023] An X-ray source according to one aspect of the present 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 controller that controls the light source and the deflector, wherein the controller controls the deflector so as to deflect the traveling direction of the photoelectrons or ions in either a first time period from when the photoelectrons are emitted from the photocathode in response 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." 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 according to one aspect of the present disclosure may be

[18] "the X-ray source according to

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

[0025] According to one aspect of the present disclosure, it is possible to provide an X-ray source that can effectively focus photoelectrons. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 2 is a perspective view of an X-ray source according to an embodiment. [Figure 2]FIG. 2 is a cross-sectional view of the X-ray source of FIG. 1. [Figure 3] FIG. 3 is an enlarged view of a portion of the cross-sectional view of FIG. 2. [Figure 4] 1A and 1B are diagrams for explaining the ease of bending of photoelectrons. [Figure 5] 10(a) and 10(b) are diagrams for explaining the case where photoelectrons are accelerated by a mesh electrode. [Figure 6] FIG. 10 is a cross-sectional view of an X-ray source according to a first modified example. [Figure 7] 10(a) and 10(b) are diagrams for explaining a case where the traveling direction of ions is deflected by a deflection plate. [Figure 8] 10(a) and 10(b) are diagrams for explaining a case where the traveling direction of photoelectrons is deflected by a deflection plate. [Figure 9] FIG. 10 is a diagram showing a state in which the deflection plates are arranged at an angle. [Figure 10] FIG. 10 is a cross-sectional view of an X-ray source according to a second modified example. [Figure 11] 11(a) and 11(b) are diagrams showing an example of the arrangement of the coils in FIG. 10. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following description, the same or equivalent elements will be designated by the same reference numerals, and redundant description will be omitted. [Embodiment]

[0028] As shown in FIGS. 1 to 3, the X-ray source 1 includes 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 (pulsed X-rays). The X-ray source 1 is used, for example, for X-ray imaging, scientific measurements using X-rays, etc. An example of scientific measurements is time-resolved measurements such as CT (Computed Tomography) using TOF (Time Of Flight) technology.

[0029] The X-ray generation unit 2 has a target 24 that generates X-rays in response to the incidence of photoelectrons E emitted from the photoelectron generation unit 3. The photoelectron generation 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 referred to as the X direction, the direction perpendicular to the X direction (the depth direction in the paper in FIGS. 2 and 3) will be referred to as the Y direction, and the direction perpendicular to the X direction and the Y direction (the up-down direction in the paper in FIGS. 2 and 3) will be referred to as the Z direction. A vacuum envelope that defines a vacuum internal space is composed of a cylindrical portion 21 and a bulb portion 22 of the X-ray generation unit 2, which will be described later, and a light entrance window 31, a cylindrical portion 33, a cylindrical portion 34, and a cylindrical member 36 of the photoelectron generation unit 3, which will be described later.

[0030] The X-ray generating unit 2 has a cylindrical portion 21, a bulb 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 formed from, for example, a metal. An X-ray exit window 25 is attached to one end portion 21a of the cylindrical portion 21 in the Z direction. The X-ray exit window 25 is formed from a material made of a light element with high X-ray transmittance, such as beryllium. The cylindrical portion 21 is formed with a through-hole 21c that penetrates the cylindrical portion 21 along the X direction. The through-hole 21c is formed in a position facing the photocathode 32 in the X direction. The through-hole 21c is formed in, for example, a cylindrical shape with a center line along the X direction.

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

[0032] The anode section 23 is disposed, for example, inside the cylindrical section 21 and the bulb section 22, and is formed in a cylindrical shape with a centerline along the Z direction. The anode section 23 is held on the top 22a of the bulb section 22 via an anode holder 27. A cylindrical section 28 is attached to the end 23a of the anode section 23 on the X-ray exit window 25 side. The cylindrical section 28 is formed to surround the end 23a. A through-hole 28a is formed in the cylindrical section 28, penetrating the cylindrical section 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. An inclined surface 23b is formed in the end 23a, inclined with respect to the centerline of the anode section 23, so as to face the X-ray exit window 25 and the through-hole 21c. The inclined surface 23b faces the photocathode 32 via the through hole 21c. The anode portion 23 is made of, for example, a metal. In use, a positive voltage, for example, 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 reflection-type X-ray source equipped with a reflection-type target 24 that outputs X-rays XL in the reflection direction, but it may also be a transmission-type X-ray source equipped with a transmission-type target that outputs X-rays XL in the transmission direction. The X-rays XL generated in the target 24 travel toward the X-ray exit window 25. The target 24 is made of a heavy metal with a high atomic number, such as tungsten. The target 24 is in contact with the anode 23, and the potential of the target 24 is equal to the potential of the anode 23.

[0034] The photoelectron generating unit 3 includes a light entrance 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 entrance window 31 is disposed to face the target 24 in the X direction. The light entrance window 31 is formed, for example, in a disk shape with its thickness direction in the X direction. The light entrance window 31 has a surface 31a facing the target 24. The surface 31a is curved so as to be recessed toward the side opposite the target 24. The surface 31a is curved so as to be recessed toward the side opposite the focusing electrode 40 (described below). The light entrance window 31 is formed of a light-transmitting material (e.g., glass). Hereinafter, in the X direction, the side of the light entrance window 31 on which the target 24 is located (the right side in FIG. 3) will be referred to as a first side S1, and the side opposite the first side S1 (the left side in FIG. 3) will be referred to as a second side S2.

[0035] The photocathode 32 is formed on the surface 31a of the light entrance window 31. The photocathode 32 is curved along the surface 31a. That is, the photocathode 32 is curved so as to be recessed toward the side opposite to the focusing electrode 40 (second side S2), which will be described later. The photocathode 32 emits photoelectrons E in response to the incidence of pulsed light L output from the light source 4, which will be described later. Specifically, the pulsed light L that enters the light entrance window 31 from the second side S2 and transmits through the light entrance window 31 is incident on the photocathode 32, and the photocathode 32 emits pulsed photoelectrons E (pulse electrons) toward the first side S1 in response to the incidence of the pulsed light L. The pulsed light L is incident on a light entrance portion 31b of the light entrance window 31. The photocathode 32 emits photoelectrons E from a portion that overlaps with the light entrance portion 31b of the light entrance 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 portion 37, which will be described later. In use, a negative voltage is applied to the photocathode 32, for example, via the connection portion 37. The photocathode 32 is, for example, an Na-K bialkali photocathode. The photocathode 32 may be formed from a material that does not contain cesium. In this case, the durability of the photocathode 32 against collisions of ions (ion feedback) that are generated in the target 24 when photoelectrons E are incident, and are emitted from the target 24 and directed toward the photocathode 32 can be improved.

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

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

[0038] The focusing electrode 40 is disposed 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] Focusing electrode 40 has a cylindrical portion 41 and a connecting portion 42. Cylindrical portion 41 is formed in a cylindrical shape with a center line along the X direction (the direction in which focusing electrode 40 faces photocathode 32). In use, a negative voltage is applied to cylindrical portion 41 of focusing electrode 40 via connecting portion 42, for example.

[0040] The tubular 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 photocathode 32 and a surface 44b (first curved surface) opposite to the surface 44a. The surface 44a is curved so as to be convex toward the photocathode 32, and is curved so as to fit along the photocathode 32. The surface 44b faces the acceleration electrode 50 arranged inside the cylindrical portion 41. The surface 44b is curved so as to be concave toward the side opposite the acceleration electrode 50 (second side S2). In this example, the surface 44b is curved so as to fit along the surface 44a. The surface 44b forms a part of the surface 40a of the focusing electrode 40 facing the acceleration electrode 50. In other words, the surface 40a has the surface 44b.

[0042] The curved portion 44 has a through-hole 44c that penetrates an 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 passing hole) through which photoelectrons E emitted from the photocathode 32 pass. The through-hole 44c is formed in the curved portion 44 at a position that overlaps with the light entrance portion 31b of the light entrance window 31 when viewed from the X direction. 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 the shape of an annular plate, 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 in a circular ring shape when viewed from the X direction, for example, and is connected to the cylindrical portion 41 at 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 from between the cylindrical portion 33 and the cylindrical portion 34 to the outside.

[0044] The acceleration electrode 50 is disposed between the focusing electrode 40 and the target 24. In other words, if the direction in which the photoelectrons E emitted from the photocathode 32 travel toward the target 24 is defined as the traveling direction of the photoelectrons E, the acceleration electrode 50 is disposed downstream of the focusing electrode 40 in the traveling direction of the photoelectrons E. In other words, the focusing electrode 40 and the acceleration electrode 50 are disposed so that the photoelectrons E emitted from the photocathode 32 pass through the through-holes 44c, which are electron passage holes, of the focusing electrode 40, and then through the through-holes 54c (described below), which are electron passage holes of the acceleration electrode 50.

[0045] In this example, the acceleration electrode 50 is arranged so as to overlap a portion 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, a first cylindrical portion 53 of the acceleration electrode 50, which will be described later, overlaps a portion of the cylindrical portion 43 and the curved portion 44 of the focusing electrode 40. In this 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 photoelectrons E that are emitted from the photocathode 32 and pass through the through-holes 44c of the focusing electrode 40. The acceleration electrode 50 is made of, for example, a 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 with 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, when in use.

[0047] The tubular 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 circular plate shape having a center line along the X direction. The bottom plate portion 54 is arranged so as to overlap a portion 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 opposite to 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 flat 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 in a flat shape along a plane perpendicular to the X direction, for example.

[0049] The bottom plate portion 54 has through-holes 54c penetrating the bottom plate portion 54 along the X direction. The through-holes 54c are through-holes (photoelectron passing holes) through which photoelectrons E pass after passing through the through-holes 44c of the focusing electrode 40. The through-holes 54c are formed in the bottom plate portion 54 at positions overlapping with the focusing electrode 40 when viewed from the X direction. The through-holes 54c are formed, for example, in a cylindrical shape with a center line along the X direction. The diameter of the through-holes 54c is, for example, smaller than the diameter of the through-holes 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 so as to extend outward from the end of the first side S1 of the first cylindrical portion 53. The second cylindrical portion 56 extends in an upright manner 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 so as 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 acceleration electrode 50 has a first space P11 and a second space P12. The first space P11 is, for example, a space defined by the through-hole 54c. The first space P11 is located on the side of the focusing electrode 40 (second side S2) in the space P1. The first space P11 is, for example, formed in a cylindrical shape with 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 the space P1. The second space P12 is, for example, formed in a cylindrical shape with 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 a circular ring shape when viewed from the X direction, for example, 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 drawn out from the first side S1 of the cylindrical portion 34 to the outside.

[0053] The cylindrical member 36 is disposed 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 along the X direction from the through-hole 21c of the cylindrical portion 21 toward the photocathode 32, and is disposed so that an end of the second side S2 of the cylindrical member 36 faces 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 81 and an insertion portion 82. An end portion 81a on the second side S2 of the main body 81 is disposed inside the second cylindrical portion 56 of the acceleration 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 acceleration electrode 50 via the connecting portion 83, and the potential of the cylindrical member 36 is equal to the potential of the acceleration electrode 50.

[0055] The insertion portion 82 is formed at the end of the first side S1 of the main body 81. The diameter of the insertion portion 82 is smaller than the diameter of the main body 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. In other words, since the cylindrical member 36 is in contact with both the acceleration electrode 50 and the cylindrical portion 21, the potentials of the acceleration electrode 50, the cylindrical member 36, and the cylindrical portion 21 are equal. A through-hole 82a penetrating along the X direction is formed at the end of the first side S1 of the insertion portion 82.

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

[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 the pulsed light L at a predetermined timing, for example, at a predetermined cycle, under the control of the control unit 5. The control unit 5 is, for example, configured by 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 use, voltages are applied to the photocathode 32, the focusing electrode 40, and the anode 23. The acceleration electrode 50 and the cylindrical member 36 are grounded. For example, a voltage of −2.5 kV is applied to the photocathode 32, a voltage of −3 kV is applied to the focusing electrode 40, and a voltage of 120 kV is applied to the anode 23. Because the acceleration electrode 50 and the cylindrical member 36 are grounded, their potentials are 0 kV. In other words, with the acceleration electrode 50 and the cylindrical member 36 at 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 23. In use, pulsed light L is first output from the light source 4 toward the light entrance window 31. When the pulsed light L passes through the light entrance window 31 and enters the photocathode 32, photoelectrons E are emitted from the photocathode 32 toward the target 24. The photoelectrons E form a pulsed electron beam. The photoelectrons E are accelerated toward the target 24 by the acceleration 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 acceleration electrode 50.

[0059] Here, in the X-ray source 1, a focusing electrode 40 is disposed between the photocathode 32 and the accelerating electrode 50. As a result, the photoelectrons E are focused by the focusing electrode 40 while being accelerated by the accelerating electrode 50. Therefore, the photoelectrons E, which have a relatively low energy before being accelerated by the accelerating electrode 50, can be focused, and the photoelectrons E can be well focused.

[0060] The photoelectrons E that have passed through the accelerating electrode 50 pass through the equipotential space P2 inside the cylindrical member 36. Because the cylindrical member 36 is 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 (120 kV in this example) between the cylindrical member 36 and the target 24. The photoelectrons E then enter the target 24. The target 24 generates pulsed X-rays XL due to the incidence of the photoelectrons E. The X-rays XL generated in the target 24 pass through the X-ray exit window 25 and are emitted to the outside of the X-ray source 1. [Action and effect]

[0061] In the X-ray source 1, the focusing electrode 40 is disposed to face the photocathode 32, and the accelerating electrode 50 is disposed between the focusing electrode 40 and the target 24. In other words, the accelerating electrode 50 is disposed after the focusing electrode 40 in the traveling direction of the photoelectrons E. This makes it possible to focus the photoelectrons E, which have a relatively low energy before being accelerated by the accelerating electrode 50, and to focus the photoelectrons E well.

[0062] As shown in FIG. 4(a), photoelectrons E emitted from the photocathode 32 are accelerated toward the accelerating electrode 50, increasing their energy. FIG. 4(a) shows multiple equipotential surfaces ES. The size of the circle representing the photoelectron E in the figure indicates the energy of the photoelectron E, which gradually increases as the photoelectron E accelerates from left to right. As shown in FIG. 4(b), when photoelectrons E1, E2, and E3 are bent by focusing electrodes, photoelectron E1, which has the lowest energy, is the easiest to bend, and photoelectron E3, which has the highest energy, is the most difficult to bend. Therefore, photoelectrons E in a high-energy state are more difficult to focus than photoelectrons E in a low-energy state. Therefore, to focus photoelectrons E to the same extent, a high voltage must be applied to the focusing electrodes to form a strong electric field (electrostatic lens). Alternatively, assuming the same voltage is applied to the focusing electrodes, it is more difficult to focus photoelectrons E in a high-energy state (to a fine focus) than photoelectrons E in a low-energy state.

[0063] Thus, when the acceleration electrode is disposed between the photocathode and the focusing electrode, high-energy photoelectrons accelerated by the acceleration electrode are focused, requiring a high voltage to be applied to the focusing electrode. Alternatively, when high-energy photoelectrons E are focused using the same voltage, the focal length becomes long, which may result in an increase in the device size or a large focusing diameter (making it difficult to achieve a fine focus). On the other hand, in the X-ray source 1 according to this embodiment, the acceleration electrode 50 is disposed downstream of the focusing electrode 40 in the traveling direction of the photoelectrons E, and is capable of focusing photoelectrons E with relatively low energy before being accelerated by the acceleration electrode 50. This allows the voltage applied to the focusing electrode 40 to be reduced, or the photoelectrons E to be focused to a fine focus.

[0064] The acceleration electrode 50 is arranged so as to overlap a part 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 acceleration electrode 50 to be brought close to the focusing electrode 40, and the photoelectrons E can be accelerated well.

[0065] The focusing electrode 40 has a cylindrical portion 41 having a center line along the direction in which the focusing electrode 40 faces the photocathode 32, and the accelerating electrode 50 is disposed inside the cylindrical portion 41 of the focusing electrode 40. This allows the accelerating electrode to be close to the focusing electrode, thereby enabling good acceleration of photoelectrons.

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

[0067] FIG. 5 is a diagram illustrating the trajectories of photoelectrons E when photoelectrons E emitted from the photocathode 132 are accelerated using a mesh electrode A. FIG. 5(a) illustrates multiple equipotential surfaces ES. The trajectories of photoelectrons E4 to E7 are also illustrated as an example of the trajectories of photoelectrons E. As illustrated in FIG. 5(a), the equipotential surfaces ES may become more distorted in a wavy manner as the photoelectrons approach the mesh electrode A. In this case, the trajectories of photoelectrons E may be unaffected by the distortion of the equipotential surfaces ES, as in the case of photoelectrons E4 and E5, or may be curved due to the distortion of the equipotential surfaces ES, as in the case of photoelectron E6. Therefore, as illustrated in FIG. 5(b), the trajectories of photoelectrons E may become uneven, making it difficult to focus the photoelectrons E at a single point. Furthermore, as illustrated in FIG. 5(a), the photoelectrons E may collide with the mesh electrode A and be annihilated. In contrast, in this embodiment, the accelerating electrode 50 has a cylindrical portion 51. In other words, the photoelectron passing hole (through hole 54c of the acceleration electrode 50) is composed of a single through hole provided in the electrode, and is not composed of a photoelectron passing hole partitioned by a lattice-like or net-like member such as a mesh electrode. Therefore, as described above, it is possible to suppress unevenness in the trajectory of the photoelectrons E, and it is possible to suppress loss of photoelectrons E.

[0068] Surface 40a of focusing electrode 40 has surface 44b (first curved surface) curved so as to be recessed toward the opposite side from accelerating electrode 50, and cylindrical portion 51 of accelerating electrode 50 has curved region R2 (second curved surface) curved so as to be convex toward surface 44b of focusing electrode 40. This makes it possible to suppress the occurrence of discharge between focusing electrode 40 and accelerating electrode 50.

[0069] The photocathode 32 is curved so as to be recessed toward the opposite side from the focusing electrode 40. This allows the photoelectrons E to be emitted in a state that makes it easy to focus them well.

[0070] A surface 44a of the curved portion 44 of the focusing electrode 40 that faces the photocathode 32 is curved to fit the photocathode 32. This allows the photoelectrons E emitted from the photocathode to be focused more effectively.

[0071] In the acceleration electrode 50, the second space P12 inside the through-hole 54c has a diameter larger than the first space P11 inside the cylindrical portion 51. By forming the second space P12 in this manner, it is possible to prevent the 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 the same potential throughout, and defines an equipotential space P2 therein through which photoelectrons E pass. This makes it possible to provide an equipotential space P2 that can be used, for example, to deflect the traveling direction of photoelectrons E emitted from the photocathode 32 and traveling toward the target 24, or of ions I that are generated in the target 24 when photoelectrons E are incident and travel from the target 24 toward the photocathode 32. For example, the traveling direction of the photoelectrons E or the 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, because the electron trajectories on the first side S1 and the second side S2 in the equipotential space P2 can be designed independently, the characteristics of the electron trajectories can be easily optimized. [First Modification]

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

[0074] The tubular portion 41 of the focusing electrode 40 in the first modification 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 according to the embodiment, and therefore will not be described here.

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

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

[0077] The inclined portion 44A has a through-hole 44c that penetrates an 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 entrance portion 31b of the light entrance window 31 when viewed from the X direction. The through-hole 44c is formed, for example, in a cylindrical shape with a center line along the X direction.

[0078] The cylindrical portion 51 of the acceleration electrode 50 in the first modified example 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 configurations as the first flange portion 55, the second cylindrical portion 56, and the second flange portion 57 according to the embodiment, respectively, and therefore will not be described here.

[0079] The first cylindrical portion 53A is formed in a cylindrical shape with 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. In other words, the thickness of the cylindrical portion 53A2 is larger than the thickness of the cylindrical portion 53A1.

[0080] A pair of second air holes 53a are formed in the first cylindrical portion 53A, penetrating the first cylindrical portion 53A along the Z direction. The pair of second air holes 53a are formed, for example, on both sides of the center line of the first cylindrical portion 53A in the Z direction of the first cylindrical portion 53A. The second air holes 53a are formed, for example, in a circular shape when viewed from the Z direction. The second air holes 53a are formed at positions overlapping with the first air holes 43a of the focusing electrode 40 when viewed from the Z direction. The diameter of the second air holes 53a is smaller than the diameter of the first air holes 43a of the focusing electrode 40.

[0081] A space P1 inside the cylindrical portion 51 of the accelerating electrode 50 is connected to a space P3 outside the cylindrical portion 41 of the focusing electrode 40 via the first air hole 43a and the second air hole 53a. The space P3 is, for example, a 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) facing the surface 44b of the inclined portion 44A of the focusing electrode 40, and a surface 54b opposite to the surface 54a. The surface 54a is inclined so as to move away from the center line of the focusing electrode 40 as it becomes farther from the focusing electrode 40. The surface 54a faces the surface 44b of the inclined portion 44A of the focusing electrode 40. The surface 54a is formed, for example, in an annular shape surrounding a through hole 54c (described later) when viewed from the X direction. The surface 54b is formed, for example, in a planar shape along a plane perpendicular to the X direction.

[0083] As described above, the X-ray source 1A according to the first modification further includes a deflector 6. The deflector 6 deflects, in the equipotential space P2, the traveling direction of photoelectrons E emitted from the photocathode 32 toward the target 24, or ions I ( FIG. 7( b) ) generated in the target 24 when the photoelectrons E are incident and traveling from the target 24 toward the photocathode 32. The ions I are, for example, positive ions generated when the photoelectrons E are incident on the target 24. The ions I are, for example, positive ions generated when residual gas adhering to the target 24 is ionized by collision with the photoelectrons E. Without the deflector 6, these positive ions traveling from the target 24 toward the photocathode 32 and colliding with the photocathode 32 may damage the photocathode 32 (ion feedback). Deflecting the traveling direction of the photoelectrons E or ions I using the deflector 6 can prevent such damage to the photocathode 32.

[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 across the center line of the cylindrical member 36. The deflection plates 84 generate an electric field (deflection electric field) for deflecting the traveling direction of the photoelectrons E or the 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 traveling direction of the photoelectrons E or the ions I is deflected by the electric field when the photoelectrons E or the 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. The control unit 5 does not perform control to deflect the photoelectrons E during a first time period from when photoelectrons E are emitted from the photocathode 32 in response to the incidence of the pulsed light L until the photoelectrons E are incident on the target 24. On the other hand, during a 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 the deflector 6 deflects the traveling direction of the ions I. That is, in this example, the deflector 6 deflects the traveling direction of the ions I, not the traveling direction of the photoelectrons E.

[0086] FIG. 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 traveling direction of photoelectrons E emitted from the photocathode 32 is not deflected by the deflection plates 84 (FIG. 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 traveling direction of ions I is deflected (FIG. 7(b)).

[0087] For example, if the length of the 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 the pair of deflection plates 84 face each other is 10 mm, applying a voltage of 10 kV to the pair of deflection plates 84 can bend ions I in the Z direction by 1.8 mm at the exit of the deflection plates 84.

[0088] In this way, by generating an electric field only in the second time period T2 when photoelectrons E are not emitted, it is possible to deflect only the traveling direction of the ions I. This makes it possible, for example, to cause the ions I to collide with a portion of the photocathode 32 other than the photoelectron emission point Q. Therefore, damage caused by the collision of the ions I with the photoelectron emission point Q of the photocathode 32 can be suppressed. Here, even the lightest ions, hydrogen ions, are heavier than the photoelectrons E. Therefore, when the photoelectrons E and hydrogen ions are accelerated with the same potential difference, the difference in speed between the two is about 40 times. Therefore, by generating an electric field only in the second time period T2, it is possible to favorably bend the slow-moving ions I.

[0089] Similarly to the above embodiment, the first modification also makes it possible to focus photoelectrons E having a relatively low energy before being accelerated by the acceleration electrode 50, thereby enabling good focusing of the photoelectrons E. Furthermore, in the first modification, the surface 40a of the focusing electrode 40 has a surface 44b (first inclined surface) that is inclined so as to move away from the center line of the focusing electrode 40 as it approaches the acceleration electrode 50, and the inclined portion 54A of the cylindrical portion 51 of the acceleration electrode 50 is disposed 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 as to move away from the center line of the acceleration electrode 50 as it moves away from the focusing electrode 40. This makes it possible to suppress the occurrence of discharge between the focusing electrode 40 and the acceleration electrode 50, similar to the embodiment.

[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 air hole 43a and the second air hole 53a. This allows the inside of the X-ray source to be satisfactorily evacuated. For example, when gas such as air is removed from the inside of the X-ray source 1A to evacuate the inside of the X-ray source 1A, the gas can be prevented from remaining in the space P1 inside the accelerating electrode 50.

[0091] The X-ray source 1A includes a deflector 6 that deflects, in the equipotential space P2, the direction of travel of photoelectrons E emitted from the photocathode 32 and heading toward the target 24, or of ions I that are generated in the target 24 when the photoelectrons E are incident and that head from the target 24 toward the photocathode 32. This makes it possible to suppress damage to the photocathode due to collisions of the ions I.

[0092] The deflector 6 has a pair of deflection plates 84 that generate an electric field for deflecting the traveling direction of the photoelectrons E or ions I, and the pair of deflection plates 84 are arranged to face each other in a direction (Z direction) perpendicular to the direction in which the focusing electrode 40 faces the photocathode 32. This allows the traveling direction of the photoelectrons E or ions I to 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 the deflector 6 deflects the traveling direction of the ions I during a 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. In this case, when X-rays are generated using the pulsed light L, damage to the photocathode 32 due to collisions of the ions I can be suppressed.

[0094] In the above example, the traveling direction of the ions I is deflected. However, as shown in FIG. 8, the traveling direction of the photoelectrons E may also be deflected. In this case, the control unit 5 applies a voltage to a pair of deflection plates 84 in a first time period T1 to generate an electric field. This deflects the traveling direction of the photoelectrons E (FIG. 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. Furthermore, when deflecting the traveling direction of the ions I, the control unit 5 does not apply a voltage to the pair of deflection plates 84 in a second time period T2 to generate an electric field. Therefore, the traveling direction of the ions I is not deflected (FIG. 8(b)).

[0095] In this way, by applying a voltage to the pair of deflection plates 84 only during the first time period, it is possible to deflect only the traveling direction of the photoelectrons E. In this case, the target 24 is positioned offset in the Z direction with respect to the photoelectron emission point Q of the photocathode 32, so that the ions I traveling from the target 24 to the photocathode 32 can be made to collide with a portion of the photocathode 32 other than the photoelectron emission point Q. Therefore, even in this case, damage caused by collision of the 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. Therefore, the photoelectrons E after acceleration by the accelerating electrode 50 are easier to deflect than the ions I, and the photoelectrons E can be easily deflected. This allows, for example, the size of the pair of deflection plates 84 to be reduced. Alternatively, the voltage (deflection voltage) applied to the pair of deflection plates 84 can be reduced. For example, when photoelectrons E accelerated by a potential difference of 3 kV and ions I accelerated by a potential difference of 120 kV are deflected, the photoelectrons E require 1 / 40 of the deflection voltage required for the ions I to achieve the same displacement.

[0097] As described above, the control unit 5 may control the deflector 6 in the first time zone T1 so that the deflector 6 deflects the traveling direction of the photoelectrons E or the ions I. This makes it easier to deflect the photoelectrons after acceleration by the accelerating electrode 50 compared to the ions I generated in the target 24, and therefore the photoelectrons can be easily deflected.

[0098] In the first modified example, the pair of deflection plates 84 are arranged parallel to each other. However, as shown in FIG. 9 , the pair of deflection plates 84 may be arranged at an angle 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 toward the target 24. Even in this case, the traveling direction of the photoelectrons or ions can be deflected by the electric field generated by the pair of deflection plates 84. Furthermore, the photoelectrons E can be prevented 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 photoelectrons E, the higher the efficiency with which the pair of deflection plates 84 bend the photoelectrons E. However, if the pair of deflection plates 84 are brought too close to the electron beam of photoelectrons E, the deflected electron beam may come into contact with the deflection plates 84, resulting in a loss of the photoelectrons E reaching the target 24. In contrast, by tilting the pair of deflection plates 84 as shown in FIG. 9 , the photoelectrons E can be prevented from coming into contact with the deflection plates, thereby reducing the loss of the photoelectrons E. [Second Modification]

[0099] 10 is a diagram showing an X-ray source 1B according to a second modified example. The X-ray source 1B according to the second modified example differs from the X-ray source 1A according to the first modified example in that the deflector 6 does not have a pair of deflection plates 84 but has a pair of coil units 85.

[0100] In this example, the pair of coil sections 85 are arranged outside 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, sandwiching the cylindrical member 36 therebetween. The pair of coil sections 85 generate a magnetic field M ( FIG. 11 ) for deflecting the traveling direction of the photoelectrons E or ions I. The pair of coil sections 85 generate a magnetic field M in an equipotential space P2 inside the cylindrical member 36 between the pair of coil sections 85, for example. The traveling direction of the photoelectrons E or ions I is deflected by the magnetic field M when the photoelectrons E or ions I pass between the pair of coil sections 85.

[0101] As shown in FIG. 11(a), each of the pair of coil units 85 includes a core member 85a and a coil wire 85b. The core member 85a is formed, for example, in a cylindrical shape with 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 member 85a of the pair of coil units 85 may be formed in an annular shape as shown in FIG. 11(b). In this case, the magnetic field M can be applied evenly to the periphery of the equipotential space P2 between the pair of coil units 85. Alternatively, the core member 85a may be formed of two semicircular annular members separated at the position indicated by the dashed line in FIG. 11(b), and the two semicircular annular members may be arranged to face each other.

[0102] As in the above embodiment, the second modified example also makes it possible to focus photoelectrons E having a relatively low energy before being accelerated by the accelerating electrode 50, thereby enabling good focusing of the photoelectrons E. Furthermore, in the second modified example, a pair of coil units 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). This makes it possible to deflect the traveling direction of the photoelectrons E or ions I by the magnetic field M generated by the pair of coil units 85. [Variations]

[0103] The present disclosure is not limited to the above-described embodiment and modified examples. For example, the materials and shapes of the components are not limited to those described above, and various materials and shapes can be adopted.

[0104] The acceleration electrode 50 does not have to overlap a portion 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 acceleration electrode 50 may be disposed on the first side S1 with respect to the focusing electrode 40. In this way, "the acceleration electrode is disposed between the focusing electrode and the target" includes a case in which the focusing electrode 40 and the acceleration electrode 50 do not overlap, and a case in which the focusing electrode 40 and the acceleration electrode 50 overlap. Furthermore, the entire focusing electrode 40 does not have to be disposed between the photocathode 32 and the acceleration electrode 50; it is sufficient that at least a portion of the focusing electrode 40 is located between the photocathode 32 and the acceleration electrode 50. The acceleration electrode 50 does not have to have a cylindrical portion 51 and may be, for example, flat or mesh-shaped.

[0105] The photocathode 32 does not have to be curved so as to be recessed toward the side opposite to the focusing electrode 40 (the second side S2), and may be, for example, flat. The space P1 inside the cylindrical portion 51 of the accelerating electrode 50 does not have to have the second space P12 having a diameter larger than the first space P11, and the entire space P1 may have the same diameter. The cylindrical member 36 only needs to 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, and 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 vent holes 43a formed in the cylindrical portion 41 of the focusing electrode 40 do not have to be a pair, and may be one, or three or more. The cylindrical portion 41 does not have to have any first vent holes 43a. The second vent holes 53a formed in the cylindrical portion 51 of the accelerating electrode 50 do not have to be a pair, and may be one, or three or more. The cylindrical portion 51 does not have to have any second vent holes 53a.

[0107] The pair of deflection plates 84 in the first modified example do not have to face each other in the Z direction, but may face each other in the Y direction. The deflection plates 84 do not have to be a pair, and may be only one deflection plate. The X-ray source 1A in the first modified example does not have to include the deflector 6. The pair of coil units 85 in the second modified example do not have to face each other in the Z direction, but may face each other in the Y direction. The coil unit 85 does not have to be a pair, and may be a single coil. In this case, the single coil may extend to surround the region surrounded by the pair of coil units 85 of the cylindrical member 36. The pair of coil units 85 of the deflector 6 in the second modified example do not have to be arranged outside the cylindrical member 36, and may be arranged inside the cylindrical member 36. In this case, the pair of coil units 85 can be brought closer to the trajectory of the photoelectrons E than when the pair of coil units 85 are arranged outside the cylindrical member 36, and therefore the current flowing through the coil unit 85 can be reduced. The X-ray source 1B of the second modified example does not necessarily have to include the deflector 6. The light source 4 only needs to emit pulsed light L at a predetermined timing, and does not necessarily have to emit pulsed light L periodically. [Explanation of symbols]

[0108] 1, 1A, 1B...X-ray source, 4...light source, 5...controller, 6...deflector, 41, 51...cylindrical portion, 24...target, 32...photocathode, 35...control electrode portion, 36...cylindrical member, 40...focusing electrode, 40a...surface, 43a...first vent, 44a...surface, 44b...surface (first curved surface, first inclined surface), 50...accelerating electrode, 53a...second vent, 54a...surface (second curved surface, second inclined surface), 84...deflection plate, 85...coil portion, E...photoelectrons, I...ions, 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-rays.

Claims

1. A photocathode that emits photoelectrons in response to incident light, A target that generates X-rays in response to the incidence of photoelectrons emitted from the photocathode, The system comprises a control electrode section positioned between the photocathode and the target, The control electrode section is A focusing electrode is positioned facing the photocathode and focuses the photoelectrons emitted from the photocathode, An X-ray source comprising an accelerating electrode positioned between the focusing electrode and the target for 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 focusing electrode has a cylindrical portion having a center line aligned in the direction in which the focusing electrode faces the photocathode, The X-ray source according to claim 1 or 2, wherein the accelerating electrode is arranged inside the cylindrical portion of the focusing electrode.

4. The X-ray source according to claim 1 or 2, 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 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. The X-ray source according to claim 4, wherein the cylindrical portion of the accelerating electrode is arranged to face the first curved surface and has a second curved surface that is curved to be convex toward the first curved surface.

6. The surface of the focusing electrode facing the accelerating electrode has a first inclined surface that is inclined so that it moves away from the center line of the focusing electrode as it approaches the accelerating electrode. The X-ray source according to claim 4, wherein 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 claim 1 or 2, wherein the photocathode is curved so as to be recessed 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 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. The X-ray source according to claim 3, wherein 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. Between the accelerating electrode and the target, a cylindrical metal member is positioned, having a center line aligned with the direction in which the focusing electrode faces the photocathode. The X-ray source according to claim 1 or 2, wherein the cylindrical member has the same potential throughout and defines an equipotential space through 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, 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.

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. A light source that outputs pulsed light at a predetermined timing toward the aforementioned photocathode, The system further comprises a control unit for controlling the light source and the deflector, The X-ray source according to claim 12, 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 upon 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 so that the deflector deflects the direction of propagation of the photoelectrons during the first time period.

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