Field emission device

Abstract

This field emission device 1 includes: an insulator 4 that is joined to a cathode 2 and an anode 3 to form a vacuum container 10; and an intermediate electrode 5 that is joined to the insulator 4 between the cathode 2 and the anode 3 in the vacuum container 10, and in which is formed a hole 51 through which an electron beam emitted from the cathode 2 to the anode 3 passes. The intermediate electrode 5 comprises a conductor 52 that is led out from the insulator 4 in the axial direction of the vacuum container 10, grounded via a direct current power supply 7, and connected to the anode 3.

Description

Field Emission Device

[0001] The present invention relates to the structure of a cold cathode field emission device.

[0002] 4, which is applicable to X-ray devices, electron tubes, lighting devices, etc., performs a desired function by applying a voltage between a cathode 2 and an anode 3 in a vacuum vessel 10, causing an electron beam emitted from an emitter 20 of the cathode 2 to collide with a target 30 of the anode 3 (Patent Document 1). For example, in the case of an X-ray device, it is used for fluoroscopy by X-ray irradiation.

[0003] The electron emission of the emitter 20 is determined by the electric field applied to the emitter 20. In the case of an X-ray tube with a diode structure shown in Fig. 4, the current is fixed in a one-to-one relationship with the voltage (Fig. 5), and the voltage and current cannot be adjusted independently.

[0004] Individual adjustment of the voltage and current of the field emission device 1 is possible by using a triode structure in which an intermediate electrode 5 is disposed between the cathode 2 and the anode 3 via an insulator 4, as shown in FIG. 6 (Patent Document 2).

[0005] JP 2012-104283 A JP 2011-119084 A

[0006] The efficiency of X-ray generation is very poor at less than 3%, with the remainder being converted almost entirely into heat. Therefore, cooling the anode 3 having the target 30 becomes an issue. In the case of a diode structure, direct cooling using fins or a fan is possible by grounding the anode 3 as shown in Figure 4.

[0007] On the other hand, in the case of the triode structure shown in FIG. 6, if the intermediate electrode 5 is grounded, a positive DC voltage is applied to the anode 3, making it difficult to directly cool it.

[0008] 7, if the electric field applied to the emitter 20 is generated by the difference between the DC power supply 6 connected to the cathode 2 and the DC power supply 7 connected to the intermediate electrode 5, the anode 3 can be grounded, enabling direct cooling of the anode 3. A floating power supply may be combined in place of the DC power supply 7.

[0009] Furthermore, in order to make the most of the advantage of the anode being grounded, it is desirable to use the outer peripheral surface of the anode 3 as the ground surface, such as the large-diameter cylindrical portion 31 of the anode 3 surrounding the vacuum vessel 10 shown in Fig. 8 or the cathode-side peripheral wall portion 34 provided at one end of the large-diameter cylindrical portion 31 of the anode 3 shown in Fig. 9. However, these embodiments make the device configuration complex and large, and also increase the manufacturing cost.

[0010] In view of the above, an object of the present invention is to reduce the number of parts and the size of a field emission device.

[0011] Therefore, one aspect of the field emission device of the present invention comprises an insulator joined to a cathode and an anode to form a vacuum container, an intermediate electrode joined to the insulator between the cathode and the anode within the vacuum container and having a hole through which an electron beam emitted from the cathode to the anode passes, and a conductor protruding from the intermediate electrode, drawn out from the insulator along the axial direction of the vacuum container, grounded via a DC power supply, and connected to the anode.

[0012] In one aspect of the present invention, in the field emission device, the insulator has a hollow disk portion that seals a central opening and is joined to the cathode and also joined to the anode.

[0013] In one aspect of the present invention, in the field emission device, the insulator has a cylindrical body to one end of which the cathode is joined, and a hollow disk portion provided on the outer periphery of the other end of the cylindrical body and joined to the anode.

[0014] In one aspect of the present invention, in the field emission device, the anode has a large-diameter cylindrical portion that is joined to the insulator, and a small-diameter cylindrical portion that communicates with the large-diameter cylindrical portion and contains a target that receives the electron beam.

[0015] In one aspect of the present invention, in the field emission device, one end of the large-diameter cylindrical portion is provided with a cathode-side peripheral wall portion extending along the axial direction.

[0016] According to the present invention, it is possible to reduce the number of parts and the size of the field emission device.

[0017] 1 is a schematic cross-sectional view of a field emission device including an intermediate electrode according to a first embodiment of the present invention; a cross-sectional perspective view of the field emission device according to the first embodiment; a schematic cross-sectional view of a field emission device according to a second embodiment; a schematic cross-sectional view of a field emission device having a diode structure; a relationship between voltage and current in a field emission device having a diode structure; a schematic cross-sectional view of a field emission device having a triode structure; a schematic cross-sectional view of a field emission device having a triode structure in which the intermediate electrode is grounded; a schematic cross-sectional view of a field emission device having a triode structure in which the outer peripheral surface is the ground plane; a schematic cross-sectional view of a field emission device having a triode structure in which the outer peripheral surface is the ground plane.

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0019] A field emission device 1 according to a first embodiment of the present invention shown in FIG. 1 includes a cathode 2 , an anode 3 , an insulator 4 and an intermediate electrode 5 .

[0020] The cathode 2 is joined to one end of the insulator 4 coaxially with the anode 3, the insulator 4, and the intermediate electrode 5, and together with the anode 3 and the insulator 4 form a vacuum vessel 10, and is provided with an emitter 20 that emits an electron beam to the target 30 of the anode 3 within this vacuum vessel 10. The cathode 2 is grounded and connected to the anode 3 via a DC power supply 6.

[0021] The anode 3 is a cylindrical body of different diameters coaxial with the cathode 2, insulator 4, and intermediate electrode 5, and has a large-diameter cylindrical portion 31 and a small-diameter cylindrical portion 32 that is connected to the large-diameter cylindrical portion 31 and has a smaller diameter than the large-diameter cylindrical portion 31. The inner surface of one end edge of the large-diameter cylindrical portion 31 is joined to the hollow disk portion 42 of the insulator 4. The inner surface of the end of the small-diameter cylindrical portion 32 is provided with a target 30 having an inclined surface 301 that receives an electron beam from the emitter 20 and emits X-rays. A beam window 33 that emits the X-rays to the outside is provided on the side wall of the small-diameter cylindrical portion 32. The anode 3 is connected to a DC power supply 6 and is grounded.

[0022] Furthermore, one end of the large-diameter cylindrical portion 31 of the anode 3 along the outer periphery of the hollow disk portion 42 of the insulator 4 is provided with a cathode-side peripheral wall portion 34 extending along the axial direction of the large-diameter cylindrical portion 31 (vacuum vessel 10).

[0023] The insulator 4 is joined to the cathode 2 and the anode 3 to form the vacuum vessel 10. The insulator 4 is made of a ceramic member coaxial with the cathode 2, the anode 3, and the intermediate electrode 5, and has a cylindrical portion 41 to one end of which the cathode 2 is joined, and a hollow plate portion 42 provided on the outer periphery of the other end of the cylindrical portion 41 and joined to the anode 3. In addition, a hole 43 is formed in the hollow plate portion 42 to allow the conductor 52 of the intermediate electrode 5 to lead out from inside the vacuum vessel 10.

[0024] 1 and 2 , the intermediate electrode 5 is joined to the insulator 4 between the cathode 2 and the anode 3 within the vacuum vessel 10, and includes a hollow plate 50 having a hole 51 formed therein through which an electron beam emitted from the emitter 20 of the cathode 2 to the target 30 of the anode 3 passes. Furthermore, a conductor 52 protrudes from the hollow plate 50. The conductor 52 is drawn out from the drawing hole 43 of the hollow plate 42 of the insulator 4 along the axial direction of the vacuum vessel 10, and is grounded via the DC power supply 7 and connected to the anode 3.

[0025] The cathode 2, anode 3, insulator 4, and intermediate electrode 5 are joined by vacuum brazing (for example, silver brazing) and sealed to form the vacuum vessel 10. When vacuum sealing is performed by vacuum brazing, the cathode 2, anode 3, insulator 4, and intermediate electrode 5 are assembled and vacuum brazed. The conductor 52 of the intermediate electrode 5 and the lead-out hole 43 of the insulator 4 are also vacuum brazed together. The joints of the insulator 4 are metallized to facilitate brazing, but depending on the brazing material used, the joints of the insulator 4 may not need to be metallized.

[0026] According to the above-described field emission device 1, the ceramic member region on the cathode 2 side and the ceramic member region on the anode 3 side are integrated as insulator 4, which makes it possible to reduce the number of parts in the field emission device 1. Furthermore, the configuration of the field emission device 1 is simplified, which makes it possible to reduce the size of the field emission device 1 and reduce costs.

[0027] Furthermore, the cathode 2 is grounded via the DC power supply 6 and connected to the anode 3, and the conductor 52 is drawn out from the hollow plate portion 42 along the axial direction of the intermediate electrode 5, grounded via the DC power supply 7, and connected to the anode 3, so that the outer circumferential surface of the field emission device 1 serves as the ground surface. Therefore, the advantage of the anode 3 being grounded is utilized, and direct cooling of the anode 3 is also possible.

[0028] Furthermore, the cathode-side peripheral wall portion 34 extending from one end of the large-diameter cylindrical portion 31 of the anode 3 toward the cathode 2 along the axial direction of the large-diameter cylindrical portion 31 allows the anode 3 to be fitted with surrounding application components, making it easy to incorporate the field emission device 1 into a device such as an X-ray source in a compact manner.

[0029] The insulator 4 need only be joined to the cathode 2 and the anode 3 to form the vacuum vessel 10, and therefore does not have to have a cylindrical portion 41 like the insulator 4 of embodiment 2 illustrated in Figure 3. The insulator 4 in the figure seals the central opening 40 of the hollow plate portion 42 to be joined to the cathode 2 and also to the anode 3. Alternatively, the insulator 4 may be a cylindrical body, with the cathode 2 joined to the center of one end surface of the cylindrical body, the anode 3 joined to the other end surface of the cylindrical body, and the conductor 52 of the intermediate electrode 5 extending from the one end surface. These embodiments also provide the same effects as those of embodiment 1 described above.

[0030] DESCRIPTION OF SYMBOLS 1...field emission device, 10...vacuum vessel, 2...cathode, 20...emitter, 3...anode, 30...target, 301...inclined surface, 31...large diameter cylindrical portion, 32...small diameter cylindrical portion, 33...beam window, 34...cathode side peripheral wall portion, 4...insulator, 40...central opening, 41...cylindrical portion, 42...hollow disc portion, 43...drawing hole, 5...intermediate electrode, 50...hollow disc portion, 51...hole, 52...conductor, 6, 7...DC power supply

Claims

1. A field emission device comprising: an insulator joined to a cathode and an anode to form a vacuum vessel; an intermediate electrode joined to the insulator between the cathode and the anode within the vacuum vessel, the intermediate electrode having a hole through which an electron beam emitted from the cathode to the anode passes; and a conductor protruding from the intermediate electrode, extending from the insulator along the axial direction of the vacuum vessel, grounded via a DC power supply, and connected to the anode.

2. A field emission device according to claim 1, wherein said insulator has a hollow disk portion which seals a central opening and is joined to said cathode and is joined to said anode.

3. The electric field emission device according to claim 1, characterized in that the insulator has a cylindrical body to one end of which the cathode is joined, and a hollow disk portion provided on the outer periphery of the other end of the cylindrical body and joined to the anode.

4. The field emission device according to claim 1, characterized in that the anode has a large diameter cylindrical portion joined to the insulator, and a small diameter cylindrical portion communicating with the large diameter cylindrical portion and accommodating a target that receives the electron beam.

5. The field emission device according to claim 4, wherein one end of said large diameter cylindrical portion is provided with a cathode side peripheral wall portion extending along said axial direction.

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