Output adjustment mechanism, field emission device, and output control method for field emission device

Abstract

This field emission device 1 has: an emitter unit 3 that supports an emitter 31 in a vacuum container 2; a guard electrode 4 that is provided to the outer periphery of the emitter 31 so as to be capable of coming into contact with and separating from the emitter 31 in the vacuum container 2; a target unit 5 that comprises a target 51 which faces the emitter 31 in the vacuum container 2; a grid electrode 7 that is disposed between the emitter unit 3 and the target 51; a grid electrode support 8 that extends in the direction of the emitter unit 3 from an electrode body 71 of the grid electrode 7 and that supports the grid electrode 7 so as to be capable of reciprocating motion in the axial direction; and a support holding part 10 that holds the grid electrode support 8 so as to be capable of reciprocating motion in the axial direction.

Description

Output adjustment mechanism, field emission device, and output control method for field emission device

[0001] The present invention relates to a field emission device and an electric field shielding structure that are applied to various devices such as X-ray devices, electron tubes, and lighting devices.

[0002] An example of a field emission device that can be applied to various devices such as X-ray devices, electron tubes, and lighting devices is one in which a voltage is applied between an emitter and a target that are positioned opposite each other in a vacuum chamber of a vacuum vessel, and the electron beam emitted from the emitter is caused to collide with the target, thereby achieving a desired function (for example, the radioscopic resolution of X-rays in the case of an X-ray device).

[0003] For example, the field emission device 1 of Patent Document 1 shown in Fig. 4 includes a vacuum vessel 2 in which one end and the other end of a cylindrical insulator 21 are sealed by an emitter unit 3 and a target unit 5, respectively, to form a vacuum chamber 20. A grid electrode 7 extending in the radial direction of the vacuum chamber 20 is provided between the emitter unit 3 and the target unit 5. A high-voltage power supply 11a is connected to the emitter unit 3 and the target unit 5. A high-voltage power supply 11b is connected to the grid electrode 7 and the target unit 5.

[0004] The emitter unit 3 includes an emitter 31 having an electron generating portion 30 facing the target unit 5, and an emitter support portion 33 that supports the emitter 31 within the vacuum chamber 20 and seals one end of the insulator 21.

[0005] A guard electrode 4 is provided on the outer periphery of the electron generating portion 30 of the emitter 31. The guard electrode 4 is provided on the outer periphery of the emitter 31 so as to be movable toward and away from the emitter 31, and has a cylindrical shape extending toward both ends of the vacuum chamber 20. The guard electrode 4 is supported by a guard electrode support portion 41 at one end of the insulator 21 so as to be movable in the axial direction of the vacuum vessel 2.

[0006] In the field emission device 1, the modification of the guard electrode 4 and the like to suppress the flashover phenomenon is performed by manipulating the guard electrode support part 41, moving the guard electrode 4 toward the grid electrode 7 to suppress the field emission of the emitter 31, and then applying a voltage to the guard electrode 4 to repeatedly cause discharge. This allows the modification of the guard electrode 4 and the like while suppressing the field emission of the emitter 31, thereby improving the characteristics of the field emission device.

[0007] Japanese Patent Application Laid-Open No. 2017-224399

[0008] The field emission device 1 has three electrodes: the emitter unit 3, the target unit 5, and the grid electrode 7, and therefore requires two high-voltage power supplies. Generally, the higher the tube voltage, the larger the high-voltage power supply, and the larger the overall system combining the field emission device 1 and the high-voltage power supplies becomes. Here, if the voltage is divided by the multiple resistors R1 shown in Figure 5, it is possible to apply voltage to the field emission device 1 from a single high-voltage power supply 11.

[0009] However, since the voltage on the side of resistor R1 is uniquely determined by the voltage of high-voltage power supply 11a, it is not possible to arbitrarily control the output characteristics (e.g., tube current) of the field emission device 1. Although a method of controlling the output characteristics by moving emitter 31 together with guard electrode 4 is conceivable, the moving structure and its control would be complicated.

[0010] SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an output adjusting mechanism that can arbitrarily control the output characteristics of a field emission device using a single high voltage power supply, a field emission device, and a control method thereof.

[0011] Therefore, one aspect of the present invention is an output adjustment mechanism having an emitter unit that supports an emitter in a vacuum vessel, a target unit that has a target that faces the emitter in the vacuum vessel, a guard electrode that is provided on the outer periphery of the emitter in the vacuum vessel so as to be able to move toward and away from the emitter, a grid electrode that is arranged between the emitter unit and the target, a grid electrode support that extends from an electrode main body of the grid electrode toward the emitter unit and supports the grid electrode so as to be able to reciprocate in the axial direction of the vacuum vessel, and a support holder that holds the grid electrode support so as to be able to reciprocate in the axial direction.

[0012] In one aspect of the present invention, the output adjustment mechanism further includes a grid electrode flange that is electrically connected to the grid electrode via a bellows through which the grid electrode support is inserted and that seals one end of the vacuum vessel, and the grid electrode flange is formed with an insertion hole into which the guard electrode is inserted and sealed, and an insertion hole through which the grid electrode support is inserted.

[0013] In one aspect of the present invention, in the output adjustment mechanism, the grid electrode support further includes a shielding portion that shields an outer peripheral surface of one end side of the bellows.

[0014] In one aspect of the present invention, in the output adjustment mechanism, the support holding unit operates the grid electrode support so that the distance between the grid electrode and the guard electrode decreases when a tube current of the field emission device is increased, and so that the distance increases when the tube current is decreased.

[0015] In one aspect of the present invention, the output adjustment mechanism further includes a single power supply connected between the emitter unit and the target unit, and resistors connected between the emitter unit and the grid electrode and between the target unit and the grid electrode.

[0016] In one aspect of the present invention, the output adjustment mechanism further includes an emitter unit support that supports the emitter unit so that the emitter unit can reciprocate in the axial direction.

[0017] One aspect of the present invention is a field emission device including the output adjustment mechanism.

[0018] One aspect of the present invention is an output control method for a field emission device equipped with the output adjustment mechanism, in which the support holding unit adjusts the distance between the grid electrode and the guard electrode by operating the grid electrode support, thereby controlling the tube current of the field emission device.

[0019] According to the present invention, it is possible to provide an output adjusting mechanism that can arbitrarily control the output characteristics of a field emission device using a single high voltage power supply, a field emission device, and a control method thereof.

[0020] Fig. 1 is a schematic diagram of a field emission device and its control system according to one embodiment of the present invention; Fig. 2 is a schematic cross-sectional view of the field emission device of Fig. 1; Fig. 3 is a CC cross-sectional view of Fig. 2; Fig. 4 is a schematic diagram of a conventional field emission device equipped with two power supplies; Fig. 5 is a schematic diagram of a conventional field emission device equipped with a voltage dividing resistor and a single power supply;

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0022] The control system of a field emission device 1 to which an output adjustment mechanism according to one embodiment of the present invention is applied, shown in FIG. 1 , includes a vacuum vessel 2, an emitter unit 3, a guard electrode 4, a target unit 5, an emitter unit support 6, a grid electrode 7, a grid electrode support 8, a grid electrode flange 9, a support holder 10, a high-voltage power supply 11, a resistor R1, an insulating coupling 12, a drive conversion mechanism 13, and a motor 14.

[0023] The vacuum vessel 2 forms a vacuum chamber 20 by sealing both ends of a cylindrical insulator 21 .

[0024] The emitter unit 3 is supported coaxially with the vacuum vessel 2 within the vacuum chamber 20 on one end side of the vacuum vessel 2, and comprises an emitter 31 having an electron generating part 30 that emits an electron beam L1, and an emitter support part 32 that supports the emitter 31.

[0025] The guard electrode 4 is provided on the outer periphery of the emitter 31 within the vacuum chamber 20 at one end of the vacuum vessel 2 so as to be detachable from the emitter 31, and is cylindrical in shape extending toward both ends of the vacuum chamber 20, and is supported coaxially with the vacuum vessel 2 at the other end of the vacuum chamber 20.

[0026] The target unit 5 is supported coaxially with the vacuum vessel 2 within the vacuum chamber 20 on the other end side of the vacuum vessel 2, and is provided with a target 51 facing the emitter 31, which receives the electron beam L1 from the electron generating section 30 of the emitter 31 and emits X-rays L2, etc. outside the vacuum vessel 2.

[0027] The emitter unit support 6 is inserted into a bellows 61 interposed between the inner surface of one end of the guard electrode 4 and the emitter support portion 32 , and supports the emitter support portion 32 so as to be movable in the axial direction of the vacuum vessel 2 .

[0028] The grid electrode 7 is disposed between the emitter unit 3 and the target 51 within the vacuum chamber 20, and includes an electrode body 71 having holes 70 formed therein through which the electron beam emitted from the emitter 31 to the target 51 passes.

[0029] The grid electrode support 8 extends, for example, from the electrode body 71 of the grid electrode 7 in the direction of the emitter unit 3 and is inserted into a bellows 81 to support the grid electrode 7 so that it can move freely in the axial direction of the vacuum vessel 2. The grid electrode support 8 also includes a shielding portion 82 that shields the bellows 81, thereby suppressing electric field concentration at the protruding portions of the bellows 81 on the outer circumferential surface. The form of the grid electrode support 8 is not particularly limited as long as it can support the grid electrode 7 in the radial direction of the vacuum vessel 2, and examples thereof include a pair of rod-shaped structures arranged symmetrically with respect to the axis of the vacuum vessel 2 or a plate-shaped structure with an arcuate cross section.

[0030] The grid electrode flange 9 is electrically connected to the grid electrode 7 via a bellows 81 and seals one end of the vacuum vessel 2. As shown in Fig. 3, the grid electrode flange 9 is formed with an insertion hole 91 into which the guard electrode 4 is inserted and which is sealed by an insulator 21, and an arc-shaped insertion hole 92 into which the grid electrode support 8 is inserted.

[0031] The shape of the insertion hole 92 is not limited to an arc shape as long as it allows the grid electrode support 8 to be inserted therethrough. For example, if the grid electrode support 8 is rod-shaped, the insertion hole 92 is set to have a diameter slightly larger than the outer diameter of the grid electrode support 8 and is formed in pairs symmetrically about the axis of the vacuum vessel 2 according to the arrangement of the pair of grid electrode supports 8. The grid electrode supports 8 inserted into this pair of insertion holes 92 are each surrounded by a bellows 81. Furthermore, if the insertion hole 92 is formed in an arc shape as shown in FIG. 3 , the bellows 81 may have a double bellows structure consisting of an inner bellows surrounding the outer periphery of the guard electrode 4 and an outer bellows surrounding the inner bellows across the insertion hole 92. The number of insertion holes 92 is not limited to one pair and can be set according to the number of grid electrode supports 8.

[0032] The support holding unit 10 is connected to an insulating coupling 12 and holds the grid electrode support 8 so that it can be reciprocated by a drive conversion mechanism 13. In particular, the support holding unit 10 operates the grid electrode support 8 so that the axial distance between the grid electrode 7 and the guard electrode 4 decreases when the tube current of the field emission device 1 is increased, and increases when the tube current is decreased.

[0033] The high-voltage power supply 11 is grounded and connected between the emitter unit 3 and the target unit 5 to supply a voltage to the field emission device 1 .

[0034] The resistor R 1 is connected between the emitter unit 3 and the grid electrode 7 and between the target unit 5 and the grid electrode 7 , and divides the voltage of the high-voltage power supply 11 .

[0035] The insulating coupling 12 connects the support holder 10 and the drive conversion mechanism 13 .

[0036] The drive conversion mechanism 13 converts the rotation of the motor 14 into linear reciprocating motion along the axial direction of the vacuum vessel 2 and transmits it to the insulating coupling 12. The drive conversion mechanism 13 may employ a well-known ball screw drive or piston drive system.

[0037] In the conventional field emission device 1 of FIG. 4, the output characteristics are controlled by operating the guard electrode 4, whereas in the field emission device 1 of this embodiment of FIG. 1, the output characteristics are controlled by operating the grid electrode 7 using a single high-voltage power supply 11.

[0038] The field emission device 1 of this embodiment has a single high-voltage power supply 11, and therefore cannot individually control the voltage between the target 51 and the grid electrode 7 and the voltage between the grid electrode 7 and the emitter 31. However, the tube current can be increased or decreased arbitrarily by moving the grid electrode 7 to change the axial gap between the grid electrode 7 and the emitter 31. Specifically, when the tube current is increased, the gap between the grid electrode 7 and the emitter 31 is reduced, and when the tube current is decreased, the gap is expanded.

[0039] The effect of increasing or decreasing the tube current by changing the gap between the grid electrode 7 and the emitter 31 can also be obtained by operating the guard electrode 4 or the emitter 31, but in this case, fine adjustment is not effective because even a slight change changes the electric field on the surface of the emitter 31. To confirm this, an analysis of the electric field and electron trajectories was carried out using the analytical model shown in Figure 2.

[0040] Table 1 shows a comparison of the surface electric field of the emitter 31 and the focal spot size due to the electron trajectory when the axial distance A between the grid electrode 7 and the guard electrode 4 and the axial distance B between the guard electrode 4 and the emitter 31 are changed relative to the distance GAP between the grid electrode 7 and the emitter 31.

[0041]

[0042] No. 2, in which only distance A was changed, and No. 4, in which only distance B was changed, have the same gap. However, compared to No. 1, in which distances A and B were not changed, No. 4 has a significantly lower surface electric field of the emitter 31, resulting in no electron emission, and no electron trajectory or focal spot size. This result indicates that No. 4, in which only the guard electrode 4 or the emitter 31 is operated, experiences drastic changes in the surface electric field of the emitter 31, making fine adjustment of the tube current difficult. In contrast, Nos. 2 and 3, in which only the grid electrode 7 of this embodiment is operated, achieve a desired electric field on the surface of the emitter 31, making fine adjustment of the tube current possible, compared to No. 4.

[0043] As described above, according to the field emission device 1 of this embodiment, the output characteristics of the field emission device 1 can be arbitrarily controlled by operating the grid electrode 7 using the single high-voltage power supply 11. It is believed that simultaneously moving the guard electrode 4 and the emitter 31 would produce the same effect as operating only the grid electrode 7, but the moving structure would be complicated. In contrast, according to the field emission device 1, the grid electrode 7 alone can be reciprocated by the grid electrode support 8 inserted into the insertion hole 92 of the grid electrode flange 9 shown in FIG. 3 , and the moving structure of the grid electrode 7 can be simplified.

[0044] DESCRIPTION OF SYMBOLS 1...Field emission device 2...Vacuum vessel 20...Vacuum chamber 21...Insulator 3...Emitter unit 30...Electron generating section 31...Emitter 32...Emitter support section 4...Guard electrode 5...Target unit 51...Target 6...Emitter unit support 61...Bellows 7...Grid electrode 70...Hole 71...Electrode main body 8...Grid electrode support 81...Bellows 82...Shielding section 9...Grid electrode flange 91...Insertion hole 92...Through-hole 10...Support holding section 11...High voltage power supply R1...Resistor 12...Insulating coupling 13...Drive conversion mechanism 14...Motor

Claims

1. An output adjustment mechanism comprising: an emitter unit supporting an emitter in a vacuum vessel; a target unit having a target facing the emitter in the vacuum vessel; a guard electrode provided on the outer periphery of the emitter in the vacuum vessel so as to be removably attached to the emitter; a grid electrode disposed between the emitter unit and the target; a grid electrode support extending from an electrode body of the grid electrode toward the emitter unit and supporting the grid electrode so as to be reciprocatable in the axial direction of the vacuum vessel; and a support holder holding the grid electrode support so as to be reciprocatable in the axial direction.

2. An output adjustment mechanism as claimed in claim 1, further comprising a grid electrode flange that is electrically connected to the grid electrode via a bellows through which the grid electrode support is inserted and seals one end of the vacuum vessel, wherein the grid electrode flange is formed with an insertion hole through which the guard electrode is inserted and sealed, and an insertion hole through which the grid electrode support is inserted.

3. The output adjustment mechanism according to claim 2, wherein the grid electrode support further comprises a shielding portion that shields the outer peripheral surface of one end of the bellows.

4. The output adjustment mechanism described in claim 1, characterized in that the support holding unit operates the grid electrode support so that the distance between the grid electrode and the guard electrode decreases when the tube current is increased, and so that the distance increases when the tube current is decreased.

5. The output adjustment mechanism according to claim 1, further comprising: a single power supply connected between the emitter unit and the target unit; and resistors connected between the emitter unit and the grid electrode and between the target unit and the grid electrode.

6. The output adjustment mechanism according to claim 1, further comprising an emitter unit support that supports the emitter unit so that it can reciprocate in the axial direction.

7. A field emission device comprising the output adjustment mechanism according to claim 1.

8. A method for controlling the output of a field emission device equipped with the output adjustment mechanism described in claim 1, characterized in that the support holding unit controls the tube current by adjusting the distance between the grid electrode and the guard electrode by operating the grid electrode support.

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