JPS61181038A - Electron gun for electron tube - Google Patents

Abstract

PURPOSE:To heighten dielectric strength, by providing a heater electrode inside the outer end of an electrically-insulating cylinder provided between an anode and an electrode for a heater and a cathode so as to serve as a vacuum enclosure, and by providing an electrically-insulating thin tube between the exterior of the cylinder and the vicinity of the heater electrode located in the cylinder. CONSTITUTION:A heater electrode 7 and an electrode 5 for a heater and a cathode are provided inside the outer end of an electric insulator 4. An electrically-insulating tube 12 is provided. The length of a Wehnelt cylinder can be reduced to diminish the temperature difference between the cylinder and the electrode 5 and the rise in the temperature of the inner end of the cylinder to suppress vacuum discharge. A volume from which gas is evacuated in a gas evacuation process can be also reduced to shorten the time which it takes to perform the process. When an electron gun is dipped in insulating oil, the electrically-insulating tube 12 made of Teflon or the like acts to remove air out of the gun to wet the electrode 5, an electric insulator 6 and the heater electrode 7 with the insulating oil so as to transfer heat out well. The cooling property and dielectric strength of the electron gun are thus enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to the structure of an electron gun for an electron tube such as a straight dust klystron or a traveling wave tube.

(Prior Art and its Problems) FIG. 3 is a schematic cross-sectional view of a typical structural example widely used as an electron gun for an electron tube. The cathode 3 is heated to a predetermined temperature by the heater 8, a potential difference is applied between the anode 1 and the cathode 3, and an electron beam 9t- is extracted. Reference numeral 2 denotes a focusing electrode for shaping the electron beam 9, which will hereinafter be referred to as a Wehnelt electrode.

An insulator 4 is provided between the anode 1 and the cathode 30 to provide a potential difference (hereinafter referred to as beam voltage) t. Further, an insulator 6 is provided between the heater electrode 7 and the heater m-cathode electrode 5 in order to heat the heater 8 by energizing it. In addition, since the space from which the electron beam is extracted must be kept in a vacuum, an insulator 4, a heater/cathode electrode 5
, the insulator 6, and the heater electrode 7 are all part of the vacuum envelope. The heat generated by the heater 8 is used to maintain the temperature of the cathode 3, but most of the heat, except for that which is dissipated by radiation, is transferred to the Wehnelt electrode 2t, reaches the heater-cathode electrode 5, and is surrounded by the vacuum envelope. released outside. Due to this heat transfer, the end of the Uenel upper electrode 2 closer to the anode 1 becomes considerably high in temperature.

By the way, the insulator 4 needs to have a length so that no edge discharge occurs when a beam voltage is applied. In recent years, as electron tubes have become more powerful, electron guns with higher beam voltages have become required, and some have even exceeded 100 kV. In such an electron gun, the length of the insulator 4 is 20
In the structure shown in FIG. 3, the internal volume of the electron gun becomes large and the time required for the evacuation step in the electron tube manufacturing process becomes longer. In addition, in such electron guns with high beam voltage, atmospheric discharge often occurs between the electrodes that are in contact with the atmosphere, so they are often immersed in insulating oil, but when the electron tube is operating, the Wehnelt electrode 2 is Because of its length, the temperature difference between the electrode and the heater cathode electrode 5, which serves as the discharge end, becomes large, and the temperature of the part of the Wehnelt electrode 2 near the anode 1 becomes high, causing a vacuum discharge that may impede the operation of the electron tube or cause it to be destroyed. Things happen gradually.

The present invention eliminates the drawbacks of the conventional technology and has a beam acceleration voltage of several tens of kV.
The purpose of this invention is to facilitate manufacturing and improve the withstand voltage characteristics between the beam focusing electrode and the anode in an electron gun with high voltages ranging from several hundred kV to several hundred kV.

(Means for Solving the Problems) The present invention has a heater electrode, a heater/cathode electrode, and an anode, and the space between the heater electrode and the heater/cathode electrode and between the heater/cathode electrode and the anode also serves as a vacuum envelope. The heater electrode is provided inside the lower end of the insulating cylinder, which also serves as a vacuum envelope, between the heater/cathode electrode and the anode, and It is characterized in that a thin insulator tube is provided between the vicinity of the heater electrode inside the insulating cylinder and the outside of the insulating cylinder. This tube removes the air that existed near the heater electrode inside the insulating cylinder when the electron gun was immersed in insulating oil.
, serves to prevent damage caused by contact between heater cathode electrodes, heater electrodes, etc. and insulating oil.

(Embodiment) FIG. 1 is a diagram showing an embodiment of the present invention. The difference from the conventional example shown in FIG. 3 is that the heater electrode 7 and heater cathode electrode 5 are provided inside the lower end of the insulator 4 and that an insulator pipe 12 is installed. Since the length of the rainbow Wehnelt electrode can be shortened in this configuration, the temperature difference with the heater cathode electrode 5 can be reduced, the temperature rise at the tip of the Wehnelt electrode can be reduced, and vacuum discharge can be suppressed. Moreover, the volume to be evacuated in the evacuation process can be reduced, and the time required for the evacuation process can be shortened. Furthermore, when the electron gun is immersed in the insulating oil such as a deflon pipe, the air inside escapes and the heater/cathode electrode 5, insulator 6, and heater electrode 7 are also wetted with the insulating oil. The short length of the Wehnelt electrode fully takes advantage of the heat dissipation.

FIG. 2 shows another embodiment of the present invention, in which the effects of the present invention are even more remarkable.

An anode 1 is insulated from an electron tube body 10 by an insulator 11.

(Effects of the Invention) As described above, according to the present invention, it is possible to shorten the evacuation process time in manufacturing an electron gun, and to obtain an electron gun with excellent heat radiation and pressure resistance.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional view of one embodiment of the present invention, Fig. 2 is a schematic cross-sectional view of another embodiment of the present invention, and Fig. 3 is a schematic cross-sectional view of a typical structure of a conventional electron gun. . l... Anode, 2... Wehnelt electrode,
3... cathode, 4... insulator, 5...
... Heater cathode electrode, 6 ... Insulator, 7 ... Heater electrode, 8 ... Heater, 9 ... Electron beam, lO. ...Electron tube body, 11...Insulator, 12...
Insulator Noku Eve.

Claims (1)

[Claims] It has a heater electrode, a heater cathode electrode, and an anode,
In an electron gun in which the heater electrode and the heater cathode electrode and the heater cathode electrode and the anode are insulated by an insulator that also serves as a vacuum envelope, the heater electrode is insulated between the heater cathode electrode and the anode. An electron gun for an electron tube, characterized in that a thin tube is provided inside the lower end of an insulator that also serves as a vacuum envelope, and between the vicinity of the heater electrode and the outside of the insulator.