JPS6025857B2 - electron gun - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron gun using a high-temperature heated cathode, and has the feature that the position of the electron emitting part, that is, the tip of the cathode does not displace even after long-term use. A stable electron beam can be obtained without adjustment.

For the cathode constituting the electron gun, a diluted lanthanum compound, in particular a six-shelf lanthanum compound, is used, and various structures have been proposed for devices to support this cathode.

A typical example is a device as shown in Fig. 1, in which pyrolytic graphite 2 is brought into contact with both sides of a six-shelf lanthanum cathode 1 to serve as a heat generating and support material, and a conductive electrode is formed from the outside to form a pair of electrodes. It is formed by sandwiching the compression ring between sections 3 and 4. In this structure, the cathode 1 is a Wehnelt cylinder 5.
Although the cathode base 7 is adjusted by adjusting screws 8 around it in order to locate it in the center of the opening 6 of the cathode base 7, the heat generated by the heat generating member is naturally transmitted to the guide member, causing plastic deformation in the material. There is a drawback that the cathode tip position shifts to the left or right after long-term use. In the present invention, the cathode is not sandwiched between the pair of guide members, but rather the cathode is placed around the center electrode that supports the cathode and the heating element via an insulator.
The present invention provides an electron gun having a structure in which a cylindrical external electrode is provided, and according to this device, even if the cathode is displaced in the vertical direction, that is, in the axial direction, the cathode does not deviate from the center of the bag and is not unevenly distributed. It is possible to maintain a stable electron beam for a long period of time. The configuration of the embodiment device of the present invention will be explained with reference to FIG.

1 is a six-shelf lanthanum cathode, and its part is a heating element 22
It is iron-filled inside. The heating element 22 is made of pyrolytic graphite which is electrically and thermally anisotropic, and is preferably arranged so that its layered structure is horizontal in the figure.

Reference numeral 23 denotes a center electrode made of a high-melting point metal, which contacts and supports the bottom surface of the heating element, and is disposed in a European-style cylindrical insulator 26 with sufficient dimensional accuracy, and further includes a conductive spring 24. is constantly oppressed upward by

That is, the spring 24 is configured such that its elastic force is adjusted by the adjustment screw 38 via the conductive sliding base 39. Reference numeral 27 denotes an annular heat-resistant metal plate that fixes the upper surface of the heating element 22 against the pressing force of the spring, and its outer periphery 28 is fixed to the upper surface 32 of the outer electrode 31 by spot welding or the like. A cathode protrudes into the hole 30 without contacting the disk, and the inner circumferential portion of the ring contacts the upper surface of the heating element 22 to define the spatial position of the heating element and therefore the cathode, and the center electrode 23 A current path is formed between the electrode 31 and the outer peripheral electrode 31.

The base flange 35 of the outer peripheral electrode is fastened to a cylindrical pedestal 35 fixed to the base 7 by a coupling 34. The device of the present invention is constructed as described above, and the insulator 26, the outer peripheral electrode 31, etc. are all arranged concentrically and in close contact with each other around the center electrode, especially the cathode chip. Although it may be displaced in the vertical direction due to thermal expansion, it does not change in the horizontal direction, and the
Since the beam does not deviate from the center of the beam, it is possible to emit an electron beam stably for a long period of time. Furthermore, the device of the present invention has a structure in which the insulator that defines the position of the central electrode that supports the cathode and the heating element is iron-mounted within the cylindrical pedestal, so that the position of the cathode is automatically determined and the position of the cathode is After the position of the cathode is set at a predetermined position, the outer peripheral electrode is iron-coupled to the insulator and screwed to the pedestal by means of a coupling, so there is no risk that the position of the cathode will change, and therefore manufacturing and adjustment are easy. There is an effect that can be done. Note that the heating element in the present invention is not limited to pyrolytic graphite, but can be applied not only to graphite substances having high anisotropy but also to other heating materials.

Also, an annular metal plate 27 and an outer electrode 31 that press the heating element
It may be a single piece, ie a cap-like part with a central entrance.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional device, and FIG. 2 is a sectional view of the device of the present invention. 22 is a heating element, 23 is a center electrode, 27 is an annular metal plate,
31 is a peripheral electrode. Figure 1 Figure 2

Claims (1)

[Scope of Claims] 1. A center electrode supporting a heating element to which a cathode is bonded is fitted and superimposed within a cylindrical insulator, and an outer circumferential electrode is fitted onto the outer periphery of the insulator and is fixed to the outer circumferential electrode. An electron gun characterized in that the upper surface of the heating element is brought into contact with the lower surface of the inner circumference of the annular metal plate, and the center electrode is always pressed upward by a spring. 2. The electron gun according to item 1, wherein the lower end of the spring is in contact with the conductive sliding base, and the elastic force can be adjusted by an adjustment screw. 3. The electron gun according to item 1 or 2, wherein the annular metal plate and the outer peripheral electrode are integrated. 4. The electron gun according to any one of items 1 to 3, wherein the insulator surrounding the center electrode and the peripheral electrode are formed of a cylindrical body and are disposed in close contact with each other.