JPH03159045A - Electric field emitting electron gun - Google Patents

Abstract

PURPOSE:To prevent damage of an emitter by coating a conductive member on a part opposite to an acceleration electrode of an extracting electrode via an insulating member, and making the conductive member and the emitter the same potential. CONSTITUTION:An extracting electrode 2 is placed in the vicinity of an emitter 1, a conductive member 7 is coated on a part opposite to an acceleration electrode 3 of the extracting electrode 2 via an insulating member 6, and the conductive member 7 and the emitter 1 are made to have same potential. As a result, when an electric discharge occurs between the acceleration electrode 3 and the conductive member 7, the potential of the emitter 1 also rises temporarily to a potential of the acceleration electrode 3. In the meantime the potential of the emitter 1 becomes positive with respect to the potential of the extracting electrode 2 so that generation of electrons from the emitter 1 can be temporarily stopped and excessive electron emission between the emitter 1 and the extracting electrode 2 can be prevented. Thus damage of the emitter 1 can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a field emission type electron gun whose emitter is protected.

(Prior Art) FIG. 2 shows a schematic diagram of a conventional field emission type electron gun. In the figure, 1 is an emitter, 2 is an extraction electrode, 3 is an accelerating electrode kept at ground potential, 4 is an extraction voltage power source, and 5 is an accelerating voltage power source.

In such a field emission type electron gun, when a negative high voltage is applied between the emitter 1 and the extraction electrode 2 from the extraction voltage power source 4, electrons are extracted from the emitter 1. The extracted electrons are accelerated toward a target (not shown) by an acceleration electrode 3 to which a positive high voltage is applied from the acceleration voltage power source 5 between the electrons and the emitter 1.

(Problem to be Solved by the Invention) In such a field emission electron gun, since there is a high potential difference between the extraction electrode 2 and the accelerating electrode 3, discharge may occur between the two electrodes.

When such a discharge occurs, the potential of the extraction electrode 2 temporarily rises to the potential of the accelerating electrode 3.

As a result, excessive electron emission occurs between the extraction electrode 2 and the emitter 1, and as a result, the emitter 1 is damaged.

Furthermore, when such a discharge occurs, positive ions bombard the emitter 1, which also causes damage to the emitter 1.

The present invention was made to solve such problems.
The purpose of this invention is to provide a new field emission type electron gun designed to protect the emitter.

(Means for Solving the Problems) For this purpose, the present invention provides a field emission electron gun equipped with an emitter, an extraction electrode, an accelerating electrode, and a DC power source for applying a predetermined voltage to each electrode. was installed near the emitter, and a portion of the extraction electrode facing the accelerating electrode was coated with a conductive member via an insulating member, so that the conductive member and the emitter were at the same potential.

(Embodiment) FIG. 1 is a schematic diagram of a field emission type electron gun showing an embodiment of the present invention. In the figure, the same components as in FIG. 2 are denoted by the same numbers.

In FIG. 1, the extraction electrode 2 is arranged near the emitter 1 so that the plane perpendicular to the optical axis of the extraction electrode 2 approaches a virtual horizontal plane including the tip of the emitter 1. A portion of the extraction electrode 2 facing the accelerating electrode 3 is coated with a conductive member 7 with an insulating member 6 interposed therebetween. or,
The conductive member 7 is kept at the same potential as the emitter 1. The reason for shortening the distance between the emitter 1 and the extraction electrode 2 in this way is to lower the extraction voltage necessary to obtain a desired emission current. Further, by lowering the bowing voltage, the withstand voltage of the insulating member 6 is made easier.

In a field emission type electron gun having such a structure, there is a high potential difference between the conductive member 7, which is kept at the same potential as the emitter 1, and the accelerating electrode 3. For that reason, 2
When a discharge occurs between the two, the potential of the conductive member 7 temporarily rises to the potential of the accelerating electrode 3. Therefore, the emitter 1, which is kept at the same potential as the conductive member 7, also temporarily rises to the potential of the accelerating electrode 3.

Now, due to the discharge that occurs between the accelerating electrode 3 and the conductive member 7 in this way, the potential of the emitter 1 is temporarily reduced to the accelerating electrode 3.
Therefore, the potential of the extraction electrode 2 temporarily becomes a negative potential when viewed from the emitter 1. Therefore, during that time, electrons are no longer extracted from the emitter 1, so that excessive electron emission does not occur between the emitter 1 and the extraction electrode 2. During this time, the cause of the discharge disappears and the normal operating state returns. Moreover, since the emitter 1 has a positive potential relative to the extraction electrode 2 when the discharge occurs, collision of positive ions with the emitter can be avoided.

In order to prevent creeping discharge, the holes provided at the center of the insulating member 6 and the conductive member 7 are formed to widen toward the end, as shown in FIG.

(Effects of the Invention) The present invention provides a field emission electron gun equipped with an emitter, an extraction electrode, an accelerating electrode, and a DC power source for applying a predetermined voltage to each electrode, in which the extraction electrode is installed near the emitter. , the part of the extraction electrode facing the accelerating electrode was coated with a conductive member via an insulating member, and the conductive member and the emitter were set at the same potential, so that when a discharge occurred between the accelerating electrode and the conductive member, The potential of the emitter also temporarily rises to the potential of the accelerating electrode. Therefore, during that time, the potential of the emitter becomes a positive potential with respect to the potential of the extraction electrode, so the generation of electrons from the emitter can be temporarily stopped. Electron emission can be prevented. In addition, collision of positive ions with the emitter when a discharge occurs can be avoided.
Damage to the emitter can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a field emission type electron gun showing an embodiment of the present invention, and FIG. 2 is a schematic diagram of a conventional field emission type electron gun. 1... Emitter 2... Extraction electrode 3...
Accelerating electrode 4... Extraction voltage power source 5... Accelerating piezoelectric R6... Insulating member 7... Conductive member

Claims (1)

[Claims] In a field emission electron gun equipped with an emitter, an extraction electrode, an acceleration electrode, and a DC power supply for applying a predetermined voltage to each electrode, the extraction electrode is installed near the emitter, and the acceleration electrode of the extraction electrode A field emission type electron gun characterized in that a portion facing the emitter is coated with a conductive member via an insulating member, and the conductive member and the emitter are at the same potential.