JPS60177533A - Electron gun with grid for microwave tube - Google Patents

Abstract

PURPOSE:To extremely minimize an electron beam disorder by bringing a shielding grid electrode in contact with a cathode so that the angle formed by the shielding grid electrode and a normal of the cathode face may be within a specific range. CONSTITUTION:A shielding grid electrode 2 is made of a material having thermal resistance, electric conductivity while being hard to emit electrons, for instance, pyrotechnic graphite. The shielding grid electrode 2 is attached to the cathode 1 while being equipotential to the cathode 1. The angle formed by a normal of the cathode face and the shielding grid electrode 2 is 67.5 deg. or smaller than that and larger than 0 deg.. Thereby, the shielding grid electrode can be given a beam shaping function thus being able to realize an electron gun having small disorder of the beam and uniform distribution of the cathode radiation current density.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of a grid electrode in a grid-equipped electron gun for a microwave tube.

A microwave tube is an electron gun that emits and forms an electron beam.
It consists of a high-frequency circuit that interacts with the electron beam and amplifies the high-frequency power, a collector that captures the electron beam after interaction, and a focusing device that focuses the electron beam. To operate a microwave tube in pulses, a control grid electrode is often provided near the cathode in order to control the radiation current from the cathode with small voltage changes. By applying the potential without this electrode as the voltage of the control grid electrode, beam disturbance during microwave tube operation is reduced.

Further, in order to prevent the control grid electrode from being burned out due to radiation current from the cathode, a shielding grid electrode having the same potential as the cathode is usually provided between the control grid electrode and the cathode.

However, because of this shielding grid electrode, the peripheral potential distribution is disturbed, and the shape of the electron beam is greatly disturbed. If the beam disturbance is large, the beam will enter the high frequency circuit,
This may cause heat distortion, damage the circuit, or reduce efficiency. To reduce beam turbulence, it is necessary to place the shielding grid electrode as close to the cathode as possible; however, to prevent the shielding grid electrode from melting due to the heat of the cathode, it is usually necessary to place the shielding grid electrode between the cathode and the shielding grid electrode. are spaced apart.

Such a structure has the disadvantage of large beam disturbance. In order to overcome this drawback, a structure in which a portion of the cathode is coated with pyrotic graphite to form a thin lattice has also been published. (G, J, M
i-ram and 8. L, Llen, IgDM
'l'echnical Dige-st, 290
-292.1979). However, the potential distribution between the cathode and the control grid electrode remains affected by the thin grid, and the beam disturbance is not sufficiently reduced.

The present invention provides a grid-equipped electron gun for a pulse-operated microwave tube that has a grid structure in which the disturbance of the electron beam is extremely small. In the electron gun with a grid of the present invention, a shielding grid electrode contacts the cathode, and the angle between the shielding grid electrode and the normal to the cathode surface is equal to or smaller than 67.5 degrees, and is 0 degrees. Yoshi is also big! It is assumed to be an rf signal.

By forming the shielding grid [& in this way, the disturbance of the electron beam becomes extremely small, and the distribution of the radiation current density at the cathode becomes uniform.

FIG. 1 shows the vicinity of the cathode of a prior art electron gun with a grid, where 1 is the cathode, 2 is a thin grid electrode, 3 is a control grid electrode, and 4 is a playback orbit. FIG. 2 shows an example of a grid electrode viewed from a plane perpendicular to the central axis. Normally, grid electrodes are made in a shape that is close to axial symmetry, but in order to provide an annular electrode,
It has radial spokes.

Since the inside grid electrode is set at the same potential as the one used for static elimination, the potential distribution near the cathode is disturbed and the electron orbits are also disturbed.

FIG. 3 shows the vicinity of the cathode of the electron gun with a grid according to the present invention.

The shielding grid electrode is made of a material that is heat resistant, conductive, and does not easily emit electrons, such as birotin, silica, or graphite. The grid electrode is attached to the cathode and has the same potential as the cathode. The angle between the normal to the cathode surface and the Jahei grid electrode is 67.5°, or even smaller. By setting the potential value observed at the position of the control grid electrode when there is no shielding grid electrode or control grid vL pole as the potential value of the control grid electrode, an undisturbed electron beam can be generated as shown in Figure 3. can get. The shape of the grid electrode viewed from a plane perpendicular to the central axis does not necessarily have to be nearly axially symmetrical, but may be the same as that shown in FIG. 2.

The reason why a beam with little disturbance can be obtained by adopting such a structure will be explained.

Typically, the grid 141. An electron gun without a pole consists of an anode, a cathode, and a Wehnelt electrode, as shown in FIG. 5 is an anode, and 6 is a Wehnelt electrode.

The role of the Wehnelt electrode is to shape the beam and to make the radiation current density from the cathode uniform.

It is known that if the Wehnelt electrode is made at an angle of 67.5 degrees to the normal to the cathode surface, beam disturbance will be minimized and the distribution of the radiation current density from the cathode will be even. There is. Therefore, the idea behind the grid-equipped electron gun is to provide the shield grid electrode with a uninel (t&) function to reduce beam disturbance and make the distribution of the cathode radiation current density uniform.

Figure 5 is an enlarged view of one of the inner grid electrodes.
indicates the electron emitting surface of the cathode. In FIG. 5, when the thickness of the Jahei lattice electrode is reduced, the potential at a fixed point a on the empty 1ul near the end of the electron emitting surface of the cathode increases. The number 67.5 degrees is the value when t is sufficiently large, and when s t is small, the angle between the normal to the cathode surface and the Jahei lattice 1 pole is made smaller than 67.5 degrees. ,
It is necessary to lower the potential at point a and make it the same value as when t is sufficiently large.

As explained above, the shielding grid IK pole is attached on the cathode surface, and the angle between the normal to the polar surface and the shielding grid electrode is larger than O, and is equal to or smaller than 67.5 degrees VC. By making the shielding grid electrode small, the shielding grid electrode can be given a beam shaping function, and an electron gun with small beam disturbance and a uniform cathode emission current density distribution can be realized.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 shows the vicinity of the cathode of an electron gun using a conventional insulator grid 1tL pole and a control grid mechanism. FIG. 2 shows an example of a shielding or control grid electrode as viewed from a plane perpendicular to the central axis. FIG. 3 shows the vicinity of the cathode of an electron gun having a barrier grid electrode according to the present invention. Figure 4 shows the structure of an electron gun without grid electrodes. FIG. 5 shows the shielding grid 1 according to the present invention! An enlarged view of an example of a pole (Z). 1... Cathode, 2... Shielding grid electrode, 3... Control grid electrode, 4... Electron orbit, 5... Anode, 6... Wehnelt electrode, 7... Electron emitting surface of the cathode. 1st leap? 4th ward camellia map 5

Claims (1)

[Claims] In a grid-equipped electron gun for a microphone solar wave tube consisting of a cathode, an anode, a Wehnelt electrode, a shielding grid electrode, and a control grid electrode, the shielding grid electrode is in contact with the cathode, and the line between the shielding grid electrode and the normal to the cathode surface is An electron gun with a grating for a microwave tube, characterized in that the angle formed is equal to or smaller than 67.5 degrees, and larger than 0 degrees.