JP2022148218A - Electron beam focusing mechanism and field emission device - Google Patents

Abstract

To converge the effective focal point of an electron beam from a cold cathode type electron emitter without having long and short axes or long and short sides to improve the image quality of the image captured by the electron beam.SOLUTION: An emitter cover 33 of an X-ray tube 1 has a cylindrical body 35 that can accommodate an emitter 31. An opening 330 exposing an electron emission surface 30 of an emitter 31 is formed at the end of the cylindrical body 35 facing a target unit 4. A peripheral edge 331 of the opening 330 forms a convex curved surface. In addition, the peripheral edge portion 331 has a pair of edge portions 332 facing each other and another pair of edge portions 333 that are different in height from the pair of edge portions 332 and face each other. The height of peripheral edge portion 331 gradually changes from the edge portion 332 to the edge portion 333.SELECTED DRAWING: Figure 1

Description

The present invention relates to an electron emitter applied to equipment such as an electron tube, a lighting device, an X-ray tube, and a field emission device having the same.

The X-ray tube may be of hot cathode type or cold cathode type. For example, the hot cathode X-ray tube 1 shown in FIG. 4 employs a filament 6 as an electron source. On the other hand, the cold cathode X-ray tube 1 illustrated in FIG. 5 uses an emitter 31 instead of the filament 6 as an electron source. This cold-cathode type X-ray tube 1 is superior to the hot-cathode type in that it consumes less power, can be made smaller, has a faster response speed, and has a higher density of electrons. (Non-Patent Document 1).

The focal size of the X-ray tube affects the image quality of the captured image. For example, a large focus size will result in a blurred image, while a small focus size will result in a detailed image. For this reason, in order to reduce the size of the focal spot in the X-ray tube, measures such as miniaturization of the electron source, installation of a converging cylinder, and angle of the target are adopted (for example, Patent Documents 1 and 2).

Daizo Takahashi, Toshimasa Fukai, Yuichi Nishigori, Reina Takahashi, "Development of Cold Cathode Movable X-ray Tube", Meiden Jiho Vol.360 2018 No. 3

Japanese Patent No. 4390847 Japanese Patent No. 5424098

There are two types of focal points in x-ray tubes. When the electron beam emitted from the electron source collides with the target as a thin line bundle, the area where the electron beam collides with the surface of the target and is viewed from the front is called the real focus. On the other hand, the impingement area of the target viewed from the direction of X-ray emission is called the effective focus. In general, focus means effective focus.

The effective focal region of the electron beam emitted from the filament of the hot cathode X-ray tube 1 shown in FIG. 4 forms a rectangle. The effective focus of X-rays produced by the collision of the electron beam with the target appears small on one side depending on the arrangement angle of the target. The effective focus decreases as the target placement angle decreases. If this fact is utilized, the electron beam generated from the filament will eventually approach a square even if it is rectangular, suppressing blurring of the photographed image and reducing the focal point.

On the other hand, in the cold cathode X-ray tube 1 shown in FIG. 5, the electron emission surface 30 of the emitter 31 is often circular. This is because the emitter cover 33 that protects the emitter 31 is formed in a cylindrical shape from the viewpoint of machining the parts. The effective focus of the X-rays generated when the electron beam L1 from the electron emitting surface 30 of the emitter 31 exposed through the opening 330 of the emitter cover 33 collides with the target 41 is as shown in FIG. Since it forms an ellipse and is difficult to approximate to a perfect circle, a clear image cannot be obtained.

The electron emitters disclosed in Patent Documents 1 and 2 are intended to converge the electron beam by the emitter and cover and to reduce the effective focus. not done.

In view of the above circumstances, the present invention aims to improve the image quality of an image captured by the electron beam by converging the effective focal point of the electron beam from the cold cathode type electron emitter without having long and short axes or long and short sides. is the subject.

Therefore, according to one aspect of the present invention, there is provided a cylindrical body capable of accommodating an electron emitter that emits an electron beam, the cylindrical body is formed with an opening that exposes an electron emitting surface of the electron emitter, A peripheral edge portion of the opening forms a convex curved surface, and the peripheral edge portion has a pair of opposing edge portions and another pair of opposing edge portions that are different in height from the pair of edge portions. and the height of the peripheral edge portion is an electron beam converging mechanism that gradually changes from the pair of edge portions to the other pair of edge portions.

According to one aspect of the present invention, there is provided a cylinder housing an electron emitter that emits an electron beam, an opening exposing an electron emitting surface of the electron emitter is formed in the cylinder, and the opening has a convex curved surface, and the aperture has an electron beam converging mechanism in which the radius of curvature of a pair of opposing sides is different from the radius of curvature of another pair of adjacent and opposing sides of the pair of sides. be.

In one aspect of the present invention, in the electron beam converging mechanism, the cylindrical body is a cylindrical body.

One aspect of the present invention is a field emission device having the electron beam focusing mechanism described above.

According to the present invention described above, since the effective focal point of the electron beam from the cold cathode electron emitter converges without having long and short axes or long and short sides, the image quality of the image captured by the electron beam can be improved.

1 is a schematic configuration diagram of a field emission apparatus to which one aspect of the electron beam convergence mechanism of the present invention is applied; FIG. (a) Perspective view of an emitter cover of the field emission device, (b) X sectional view and Y sectional view of the emitter cover. (a) is a diagram for explaining effective focus control in the field emission device, and (b) is a view in the direction of arrow A in (a). FIG. 4 is an explanatory view of effective focus control in a hot cathode field emission device; (a) is an explanatory view of effective focus control in a conventional cold cathode field emission device provided with an emitter cover; FIG. 2 is a plan view of an emitter cover, which is one aspect of the electron beam convergence mechanism of the present invention;

Embodiments of the present invention will be described below with reference to the drawings.

An X-ray tube 1 shown in FIG. 1 is an example of a field emission apparatus to which one aspect of the electron beam convergence mechanism of the present invention is applied. The X-ray tube 1 is a vacuum vessel in which a vacuum chamber 10 is secured within the insulator 2 by sealing one end and the other end of a cylindrical insulator 2 with an emitter unit 3 and a target unit 4, respectively. 11 are configured. A grid electrode 5 extending transversely of the vacuum chamber 10 is provided between the emitter unit 3 and the target unit 4 .

The insulator 2 is composed of cylindrical insulating members 21 and 22 made of ceramic or the like and having the same diameter. The insulating members 21 and 22 are arranged in series between the emitter unit 3 and the target unit 4 via the grid electrode 5 and brazed to form the vacuum chamber 10 .

The emitter unit 3 has an emitter 31 , an emitter support 32 and an emitter cover 33 .

The emitter 31 is one aspect of the electron emitter of the present invention. An electron beam L1 is emitted as an electron beam by applying a voltage between and.

The emitter support portion 32 supports the emitter 31 inside the emitter cover 33 . An end portion of the emitter support portion 32 is connected to an operation portion 34 for operating the emitter support portion 32 . The operation part 34 has a disc shape that can be inserted into the emitter cover 33 shown in FIG. 1, for example. It may be in the shape of a rod.

The emitter cover 33 is made of a material such as stainless steel, accommodates the emitter 31 and the emitter support section 32 , and seals the vacuum chamber 10 . The emitter cover 33 is arranged on the outer peripheral side of the electron emission surface 30 of the emitter 31, and can suppress dispersion of the electron beam L1 from the emitter 31 when the emitter 31 abuts against the emitter cover 33 due to the movement of the operation portion 34. Various forms can be applied as long as it is a material.

As a specific example of the emitter cover 33, it forms a cylindrical body 35 with a different diameter into which the emitter support portion 32 supporting the emitter 31 is inserted. An opening 330 exposing the electron emission surface 30 of the emitter 31 is formed at one end of the cylindrical body 35 facing the target unit 4 . A flange portion 37 is provided at the other end of the cylindrical body 35 to seal the vacuum chamber 10 from the end of the insulating member 22 . Further, one end of a bellows 38 is arranged at the stepped portion 36 inside the cylindrical body 35 . The bellows 38 is airtightly interposed between the stepped portion 36 in the cylindrical body 35 and the operating portion 34 and expands and contracts by operating the operating portion 34 . According to the above aspect, the mounting work of the bellows 38 is facilitated and the mounting structure is stabilized. In addition, since the diameter of the cylindrical body 35 is reduced as it approaches the one end from the other end, the electron emission surface 30 of the emitter 31 can move inside the emitter cover 33 while being guided toward the opening 330 . When the operation portion 34 is formed in the shape of a rod (not shown), the bellows 38 is airtightly interposed between the end portion of the emitter support portion 32 and the flange portion 37 and can be expanded and contracted by operating the operation portion 34. so as to be positioned within the cylindrical body 35 .

A peripheral edge portion 331 of the opening 330 of the emitter cover 33 shown in FIG. It has an edge portion 332 and another pair of edge portions 333 that are opposed to each other across a Y section perpendicular to the X section (the same applies hereinafter), which differs from the height of this edge section 332 . In addition, the peripheral edge portion 331 forms a convex curved surface, and the height gradually varies from the edge portion 332 to the edge portion 333 . For example, the height A of the edge 332 is set so as to increase toward the edge 333 and approach the height B of the edge 333 (height B>height A).

The target unit 4 includes a cylindrical target 41 facing the electron emission surface 30 of the emitter 31 and a flange portion 42 fixed to the end portion of the insulating member 21 to seal the vacuum chamber 10 . The target 41 collides with the electron beam L1 emitted from the electron emission surface 30 of the emitter 31 and emits, for example, X-rays L2. A portion of the target 41 facing the emitter 31 is provided with an inclined surface 40 inclined at a predetermined angle with respect to the electron beam L1. When the electron beam L1 collides with the inclined surface 40, the X-ray L2 is converged so that the real focus f1 of the electron beam L1 irradiated onto the target 41 (inclined surface 40) is reduced to the effective focus f2. , the beam is irradiated in a direction bent from the irradiation direction of the electron beam L1. Note that the target 41 may be provided so as to be movable along the entire length of the insulating member 21 .

The grid electrode 5 is interposed between the emitter unit 3 and the target unit 4 and appropriately controls the electron beam L1 emitted from the electron emission surface 30 of the emitter unit 3. FIG. The grid electrode 5 is arranged to extend in the transverse direction of the vacuum chamber 10, and has an electrode portion 51 formed with a passage hole 50 through which the electron beam L1 passes, and insulating members 21 and 22 connected to the electrode portion 51. and a lead-out terminal 52 led out from between.

The effects of the X-ray tube 1 of this embodiment will be described below.

The conventional cold cathode X-ray tube 1 shown in FIG. 5(a) is similar to the X-ray tube 1 of FIG. is. As a result, the actual focal point f1 of the electron beam L1 reaching the target 41 from the emitter 31 with the circular cross section S1 converges to an elliptical shape smaller than the circular cross section S1. Here, since the width of the effective focal point f2 of the electron beam L1 from the emitter 31 to the target 41 does not benefit from the arrangement angle of the inclined surface 40 on the target 41, the width of the emitter cover 33 shown in FIG. The width is substantially the same as the width of the real focal point f1 of the electron beam L1 converged only by the peripheral portion 331 . The electron beam L1 that collides with the target 41 generates X-rays L2. At this time, the effective focal point f2 of the X-ray L2 becomes elliptical because it becomes smaller than the actual focal point f1 due to the effect of the arrangement angle of the target 41 as shown in FIG.

On the other hand, in the X-ray tube 1 of this embodiment shown in FIG. 1, the peripheral edge portion 331 of the emitter cover 33, as shown in FIG. is arranged on the same plane as the minor axis a of the inclined surface 40 of the target 41 . At this time, as shown in FIG. 3A, due to the action of the pair of edge portions 332 facing each other, the real focal point f1 of the electron beam L1 reaching the target 41 becomes a circle smaller than the cross-sectional circle S1 of the emitter 31. converge. Then, as shown in FIG. 4B, due to the action of the pair of opposing edge portions 333, the real focal point f1 of the electron beam L1 converges into a circle that is further reduced compared to the convergence by the edge portion 332. FIG. As described above, by making the height of the peripheral edge portion 331 of the emitter cover 33 of this embodiment uneven, the effective focal point f2 of the X-rays L2 emitted from the target 41 is not an ellipse (or rectangle) but a perfect circle (or square). ).

Therefore, according to the X-ray tube 1 described above, the effective focus f2 of the X-ray L2 having no long and short axes (or long and short sides) can be obtained from the real focus f1 of the electron beam L1 emitted from the emitter 31. It is possible to improve the image quality of a photographed image using an electron beam from a cathode-type electron emitter.

The electron beam converging mechanism described above may be further combined with conventional techniques for converging electron beams (cover shape, grid electrode shape, emitter, grid electrode, target arrangement, etc.). According to this aspect, the effective focal point of X-rays can be further reduced, and the image quality of the captured image can be further improved.

As another aspect of the electron beam converging mechanism of the present invention, for example, an emitter cover 33 shown in FIG. 6 can be cited. The emitter cover 33 has a convex curved surface with a uniform height at the peripheral edge 331. The opening 330 has a curvature radius R1 of a pair of sides 334 facing each other across the X cross section. is different from the curvature radius R2 of the other pair of sides 335 facing each other across the Y cross section (R1>R2). This aspect also provides the same effect as the emitter cover 33 of FIG. Furthermore, if the edge portion 333 of the peripheral portion 331 in FIG. 6 is set higher than the edge portion 332, the above effect is further enhanced.

DESCRIPTION OF SYMBOLS 1... X-ray tube 10... Vacuum chamber 11... Vacuum vessel 3... Emitter unit 30... Electron emitting surface 31... Emitter 33... Emitter cover 35... Cylindrical body 330... Opening 331... Periphery, 332, 333... edges, A, B... height, 334, 335... sides, R1, R2... radius of curvature 4... target unit, 40... inclined surface, a... short axis of inclined surface 40, 41... target 5... grid electrode

Claims (4)

Having a cylindrical body capable of accommodating an electron emitter that emits an electron beam,
an opening exposing an electron emitting surface of the electron emitter is formed in the cylindrical body,
a peripheral edge of the opening forms a convex curved surface,
The peripheral edge portion has a pair of opposing edge portions and another pair of edge portions that are different in height from the pair of edge portions and face each other,
The electron beam converging mechanism, wherein the height of the peripheral edge gradually changes from the pair of edges to the other pair of edges. having a cylinder housing an electron emitter that emits an electron beam;
an opening exposing an electron emitting surface of the electron emitter is formed in the cylindrical body,
A peripheral edge of the opening forms a convex curved surface,
An electron beam converging mechanism, wherein the radius of curvature of a pair of opposing sides of said opening is different from the radius of curvature of another pair of sides adjacent to and opposing said pair of sides. 3. The electron beam converging mechanism according to claim 1, wherein said cylindrical body is a cylindrical body. A field emission apparatus having the electron beam convergence mechanism according to any one of claims 1 to 3.

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