JPH02155146A - Electron gun structure for microwave tube - Google Patents

Abstract

PURPOSE:To prevent the generation of the diode oscillation and to obtain high withstanding voltage characteristics by constructing the lower portion of the cathode supporting cylinder of an electron gun smoothly tapered or curved and larger in diameter than the upper portion of which, and the lower portion of the insulating cylinder smaller in diameter than the upper portion of which. CONSTITUTION:In a structure in which the outer surface of the cathode supporting cylinder 21 and the inner surface of the insulating cylinder 26 are faced to each other coaxially, the lower portion 21b of the cylinder 21 is made smoothly tapered or curved and larger in diameter than the upper portion 21a of which, and the lower portion 26b of the cylinder 26 connected to the stem portion is made smoothly tapered or curved and smaller in diameter than the upper portion 26a of which connected to the anode electrode 13 through metallic envelope 25 or the like. As the result, DC equipotential lines in the vicinity of the ceramic insulating cylinder 26 are generated as shown with broken lines E, so that the lines of electric force can be led out smoothly from the vacuum space to the outside of the tube with no local concentration of the energy. Thereby the generation of the diode oscillation can be made difficult and the withstanding voltage characteristics between the cathode and the anode can be improved to obtain high reliable performance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an electron gun assembly for a microwave tube, and particularly to improvements in the structure of a cathode support and an insulating cylinder surrounding the cathode support.

For example, a multi-cavity klystron, a traveling wave tube, a gyrotron, and other microwave tubes that cause an electron beam to travel generally in a straight line to oscillate or amplify microwaves are equipped with an electron gun structure that generates an electron beam.

Taking a 3 GHz band pulse klystron as an example, its microwave output is about several MW to about 100 MW, and its operating voltage reaches about 100 kV to about 450 kV. The conventional electron gun assembly has a structure as shown in FIG. The operation of the klystron will be outlined with reference to the same figure. The electron beam emitted from the electron emitting surface 12, which is a concave spherical surface of the impregnated cathode 11, is accelerated by an accelerating voltage applied between the cathode and the anode electrode 13, which also serves as the body, and is accelerated by the body provided downstream of the beam. It passes through a high frequency section consisting of a human powered cavity, an intermediate cavity, an output cavity, and a drift tube connecting them (all not shown), and interacts with the high frequency excited from the input cavity between them to have an amplification effect. Contribute to

Around the cathode 11, there is a Wehnelt electrode 1 at the same potential.
4 are arranged close to each other, and both are fixed and held on the upper part 15a of the cathode support cylinder 15. The cathode support cylinder 15 extends downward in the drawing while maintaining a constant diameter, and its lower part 15b is fixed by brazing to a cathode terminal 16 made of a thick metal ring that forms a part of the stay member, making it independent. The heater embedded in the cathode is connected to a rod-shaped heater power supply body 17. A cylindrical metal container 18 having the same potential as the anode electrode is provided surrounding the cathode and Wehnelt electrode, and an insulating cylinder 19 made of ceramic having a constant diameter is hermetically soldered to the lower end of the container, and the lower end of this insulating cylinder is connected to the cathode. It is also hermetically soldered to the terminal 16. Note that the reference numeral 20 in the figure indicates a corona ring.

In this way, the cathode support cylinder 15 and the insulating cylinder 19 are
A coaxial, axially extending insulating cylinder provides electrical isolation between the quad and the anode electrode.

(Problem to be Solved by the Invention) As shown in Figure 3, in the Lystron electron gun structure, the cathode and anode electrodes have a diode structure, so when a high DC voltage is applied between them, It is well known that the electron beam in this part operates in a space charge limited region, and that depending on the electron travel time, a negative component occurs in the resistance of this diode. Note that the transit time of electrons depends on the voltage applied to the cathode and anode, that is, the accelerating voltage, and the resistance component of the diode is the value obtained by differentiating the voltage between the two with the induced current induced between the two by the beam current.

Due to such negative resistance, an oscillation phenomenon occurs in this portion, which modulates the electron beam, adversely affecting the normal high frequency amplification function, and making the operation of the talistron unstable.

This phenomenon is called diode oscillation, and is theoretically thought to occur when the following conditions are met.

(1) A sufficiently large negative resistance is generated in the electron beam between the cathode and the anode.

(2) Forming a resonant circuit with a resonant frequency and a high Q value that meet the conditions in (1) above.

(3) The resonant circuit and the electron beam are strongly coupled in terms of high frequency.

Conventionally, measures have been taken to suppress this diode oscillation. That is, changing the travel time of the electron beam between the cathode and the anode to avoid meeting the above conditions;
Efforts are being made to lower the resonance frequency. However, the former method is difficult to implement because the perveance of the electron gun tends to deviate from the optimum value. The latter is also difficult to implement because it poses constraints on ensuring sufficient voltage resistance characteristics. Another possibility is to place a high-frequency absorber inside the electron gun structure to reduce the Q value of the resonant circuit, but the absorber may become a gas emission source or the withstand voltage characteristics may not be sufficient. There is a tendency that there is no such thing.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electron gun assembly for a microwave tube that eliminates the above-mentioned disadvantages, can suppress diode oscillation with a relatively simple configuration, and has sufficient withstand voltage characteristics.

[Structure of the Invention] (Means for Solving the Problems) In the present invention, one of the cathode support cylinders coaxially faces each other on the inner and outer surfaces, and the lower part thereof has a diameter in a smooth curved or tapered shape with respect to the upper side. A microwave tube electron gun in which the other insulating cylinder has an upper part joined to the anode electrode, and a lower part joined to the stem part has a smooth tapered or curved shape and has a small diameter. It is a structure.

(Function) According to the present invention, the cathode, the accelerating anode, and the structure in the vicinity constitute a resonant circuit with a high Q value, so that the diode oscillation phenomenon does not occur and the withstand voltage performance is sufficient. A microwave tube electron gun structure is obtained.

(Example) Examples thereof will be described below with reference to the drawings.

The same parts as in Figure 3 are designated by the same symbols.

As shown in FIG. 1, the electron-emitting cathode 11 and the Wehnelt electrode 14 are held at the illustrated upper end 21a of the cathode support cylinder 21 fixed to the stem portion. The heater for heating the cathode has legs 22 attached to two chains of a coaxial cylindrical heater power supply body 23 and a flexible ribbon 2.
They are electrically connected via 4. Wehnelt electrode I
4 has a substantially spherical funnel-shaped portion 14a, and an inner surface 25a of a metal container 25 surrounding the funnel-shaped portion 14a has a curved surface substantially concentric with the funnel-shaped portion 14a. This makes the equipotential lines in this part evenly distributed.

Therefore, the ceramic insulating cylinder 26 for electrically insulating between the cathode 11 and the anode electrode 13 has a larger diameter at the anode side upper part 26a shown in the figure and a tapered smaller diameter at the cathode side lower part 26b. and are vacuum-tightly soldered to each other by thin-walled metal rings 27 and 28 for sealing. The cathode support cylinder 21 located coaxially inside the insulating cylinder 26 has a lower end 21b having a smooth taper shape and a larger diameter from the middle of the inner region of the insulating cylinder 26 with respect to the upper end 21a on the cathode side. , is screwed and fixed near the outer peripheral edge of the cathode terminal 16 made of a thick metal ring. As a result, the cathode support cylinder 21 and the insulating cylinder 26 are configured to have opposite diameter dimensions. Several ventilation holes 21d are formed in the tapered portion 21e of the cathode support cylinder, and correspondingly, ventilation holes 23a are formed in the inner heater power supply tube 23 to reduce the exhaust conductance to the metal υF trachea 29. It's getting bigger. A lower end corona ring portion 25b of the metal container 25 and an external corona ring 30.31 are provided so as to sandwich the soldered portion of the upper portion 26a of the insulating cylinder 26 from the inside and outside. Further, a lower corona ring 32 is attached so as to surround the outside of the soldered portion of the lower portion 26b of the insulating cylinder.

When assembling, a structure is assembled in which the cathode 1 with a built-in heater and the Wehnelt electrode 14 are integrally assembled together with the cathode support cylinder 21 and the heater power supply body 23;
The metal container 25 and the assembled structure of the insulating cylinder 26 are positioned with their central axis and axial height at predetermined dimensions, and are vacuum-tightly connected at the first edge arc weld Bl. Then, these are hermetically joined to the structure surrounding the anode electrode 13 at the second edge arc weld B2, and the outer corona rings 30, 31 on the outer periphery thereof are fitted. This makes it relatively easy to assemble.

As a result of an electronic computer simulation of the electron gun structure of a pulsed klystron having such a structure, the DC equipotential lines near the ceramic insulating tube were as shown in FIG. 2. That is, since the cathode supporting cylinder has a large diameter at the bottom and the insulating cylinder has a small diameter at the bottom, the lines of electric force very smoothly exit from the vacuum region to the outside of the tube. This is obvious when compared with the equipotential line E in the conventional structure shown in FIG. In the conventional structure, the range where the electric potential is approximately equal is unnecessarily large, especially in the lower part of the insulating cylinder, and energy tends to concentrate in this part, which tends to cause a resonant circuit. This tends to cause undesired pre-dipole oscillation. On the other hand, in the case of the present invention, the potential is distributed more evenly over the entire area of the insulating cylinder, and the equipotential lines pass through the insulating cylinder almost at right angles, so that the energy is not concentrated in one part. A resonant circuit with a high Q value is less likely to occur.

Therefore, according to the present invention, the pre-dipolar oscillation phenomenon occurs inside the electron gun assembly, and the withstand voltage characteristics between the cathode and the anode are also superior to the conventional structure, resulting in highly reliable operation. can get.

In the above embodiments, the diameter of the cathode support cylinder or the insulating cylinder is tapered from the top to the bottom, but the diameter is not limited to this, and it may be formed into a smooth curve. or a combination thereof.

[Effects of the Invention] As described above, according to the present invention, the cathode, the anode, and the structure in the vicinity constitute a resonant circuit with a high Q value, so that the diode oscillation phenomenon does not occur, and A microwave tube electron gun structure with sufficient voltage resistance can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a main part showing an embodiment of the present invention, FIG. 2 is a half sectional view schematically showing equipotential lines thereof, and FIG. 3 is a longitudinal sectional view of a main part showing a conventional structure. II... Cathode, 13... Anode electrode, 21.
...Cathode support tube, 21c...Tapered part of support tube,
2B... Insulating tube, 2Ba... Upper part of insulating tube, 26b
...lower part of the insulation tube.

Claims (1)

[Scope of Claims] An electron-emitting cathode, a cathode support cylinder whose upper part supports the cathode and whose lower part is fixed to a stem member, an anode electrode arranged downstream of the beam of the cathode and having a beam passage hole; An electron gun assembly for a microwave tube, comprising an insulating tube that is spaced apart and coaxially disposed on the outer periphery of the cathode support tube, has an upper end connected to the anode electrode, and a lower end of the other end joined to the stem member. The supporting cylinder has a lower part with a smooth taper or curved shape and a larger diameter than the upper part, and the insulating cylinder has an upper part joined to the anode electrode and a lower part joined to the stem part. An electron gun structure for a microwave tube characterized by having a smooth tapered or curved shape with a small diameter.