JPS59196546A - Electron beam device - Google Patents

Abstract

PURPOSE:To obtain a device having higher insulating performance by lowering the strength of an electric field of the triple junction part according to the shape of the contacting part of an insulator and a conductor. CONSTITUTION:The base of the cylindrical projecting part 20 provided on a shield electrode 2 is closely contacted with the base of the hollow part 30 (the surface of an insulator in the hollow part) while being composed in such measure as leaving a gap of an appropriate size on the part, in which the shield electrode 2 and an insulator 3 are facing, other than said closely contacted part. Thereby, there is no electric field accelerating electrons accelerated by an electric field Ea above the figure so that said electrons are puzzled near the triple junction part 10 thus generating the electric field in the opposite direction to the electric field Ea due to field-effect of said electrons so as no more to be able to generate electron avalanche while causing no creepage flush circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron beam device, and particularly to the structure of an insulator that holds a cathode portion.

Figure 1 is a cross-sectional view showing the structure of the cathode part of a conventional electron beam device. ) is a container, (5) and (6) are flanges, (7) is a vacuum space, (8) is an insulating medium, and (9) is a stopper. Cathode part (
1) and the container (4) constitute a coaxial cylinder, with (1) being the inner cylinder and (2) being the outer cylinder. Therefore, insulator (3)
The shape of is a coaxial cone. Cathode part (11 is a hot cathode for electron beam generation, a lead wire for heating power supply, and a Wehnelt electr for beam electronic control.
ode ), etc., and a negative polarity high DC voltage is applied. The container (4) is grounded and the insulator (3)
) is the flange (5).

(6) is fixed to the container (4), the hot cathode (1) and the shield electrode (2) are held through the hole in the central axis, and these are fixed by the fastener (9). The cathode section (the hot cathode etc. in 11 is provided in the upper part of Fig. 1 and is not shown in the drawing, but the electron beam generated from this hot cathode is in the vacuum space (7) as shown in Fig. 1). The insulating medium (8) may be a vacuum, gas, liquid, etc. depending on the capacity and structure of the device.

Figure 2 is a diagram showing equipotential lines and electric field strength in the lower right part of the cross section of Figure 1. In the figure, the same symbols as in Figure 1 indicate the same parts, dotted lines are equipotential lines, and arrows are attached. The solid line is the electric field strength at the base of the arrow. Since the cathode part (1), the shield electrode (2), and the container (4) are conductors, the inside of the conductor is kept at an equal potential, and the surface thereof forms an equipotential surface. The surface potential of the shield electrode (2) is expressed by the equipotential surface (the equipotential line in the cross section shown in FIG. 2) with the surface potential of the 1001 container (4) set as 0%. Electric field strength is the ratio of potential change (i.e., potential gradient) corresponding to a minute distance change in the direction perpendicular to the equipotential lines, and it is often said that the potential gradient in a dielectric is inversely proportional to the permittivity. It is a well-known place.

In the case shown in Figure 2, the problem is the junction between the p,14 body and two types of dielectric materials with different permittivity, that is, the so-called triple junction.
This is the point shown in Figure 2 (10) at the cathode section +11 compared to the triple junction section 00.
Since the power line from the shield line #IL (2) directly enters the insulator (3) near the area, the strength of the electric field becomes relatively small as shown in Fig. 2Eb. Also, in the triple junction part (closer to the outer edge of the shield electrode (2) than 10), due to the shape of the shield electrode (2), the equipotential lines become as shown in the figure, and the electric field strength is as shown in Figure 2 Ec. On the other hand, in the triple junction section (10), the power line enters the insulator (high dielectric constant) through an extremely thin vacuum layer (low electric constant), so a relatively large portion of the potential change is caused by this thin layer. It occurs in a vacuum layer, and the potential change inside the insulator becomes smaller.

The electric field at the triple junction (11) is shown in Figure 2E.
It becomes larger as shown in a. In the part shown in Fig. 2 Ed, the distance between the 100% and 90% equipotential lines is the smallest, and the electric field Ed becomes larger, but this is not a problem because the withstand voltage between the electrodes in vacuum is large.

Now, if the electric field E at the triple junction is large, the electrons existing in the vicinity (electrons emitted by the high electric field Ea, electrons evaporated from the insulator (3), or unevenly distributed electrons) etc.) are sufficiently accelerated by the electric field EIL, resulting in an electron avalanche, which eventually leads to creeping flash at the triple junction □0.

If an attempt is made to reduce the strength of the electric field Ea by increasing the diameter of the shield electrode (2), the outer edge of the shield electrode (2) and the container (4) will become closer and Ed will increase, causing the shield electrode (2) and the container to (4) Discharge between.

The conventional device has the above-mentioned drawbacks, and the present invention was made to eliminate these drawbacks. The purpose of this invention is to provide an electron beam device with a reduced shape and higher insulation performance.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 3 is a sectional view showing an embodiment of the present invention, in which the same reference numerals as in FIG. 1 indicate the same or corresponding parts, and the shield electrode (
2) is a cylindrical protrusion provided in the insulator (3), and (to) is a cylindrical hollow portion provided in the insulator (3). The bottom surface of the protruding part is the bottom surface of the hollow part (insulator (3) in the hollow part).
(surface), and the dimensions are such that a gap of an appropriate size remains in the part other than this close contact part where the shield electric wire 1ffj1 (2) and the insulator (3) face each other. .

FIG. 4 is a diagram showing the electric field in a part of the cross section of FIG. 3, and the electric field conditions at the triple junction α0 are substantially the same as those in FIG. 2, so the electric field strength Ea is It will not be lower than Ea shown in FIG. However, in order for the creepage 1'71 circuit to occur along the insulator (3), the electrons accelerated by the electric field Ea must pass through the insulator (3) and reach the container (4). However, in the shape shown in Figure 3, there is no electric field that accelerates the electrons accelerated by Ea upwards (on the paper), so these electrons stop near the triple junction (10) and the electrons An electric field in the opposite direction to the electric field E8 is generated due to the electric field effect, and it is no longer possible to cause an electron avalanche, and no surface flashing occurs.Furthermore, the electric field inside the insulator (3) (3
) is kept at a sufficiently small value from the value that causes through-hole dielectric breakdown, so there is no risk of through-hole dielectric breakdown occurring.

As described above, according to the present invention, the insulation performance of the electron beam device can be improved by changing the shape of the insulator.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing a conventional device, Figure 2 is a diagram showing equipotential lines and electric field strength in a part of the cross section shown in Figure 1, and Figure 3 is a sectional view showing an embodiment of the present invention. , FIG. 4 is a diagram showing the electric field strength in a part of the cross section shown in FIG. 3. (1)... Cathode part, (2)... Shield electrode, (3
)... Insulator, (4)... Container, (7)... Vacuum space, (10... Triple junction part, (A)... Circular protrusion, (C)... ... Gap, (G) Kawauchi's cylindrical hollow part. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent Masuo Oiwa 259- ('J aircraft Fig. 4

Claims (1)

[Claims] A cylindrical cathode part to which a negative direct current high pressure is applied as an electron beam radiation source, a coaxial cylinder outside the coaxial cylinder with this cathode part as an inner cylinder (a grounded container constituting a fi11 cylinder, An electron device comprising: a coaxial conical insulator for holding the cathode part in the container; and a shield electrode for mitigating an electric field provided to relieve a potential gradient in the vicinity where the insulator contacts the cathode part. In the beam device, a conical protrusion that is coaxial with the axis of the cathode part and has a larger outer diameter than the outer diameter of the cathode part is provided on the side of the shield electrode facing the insulator, and A cylindrical hollow part that is coaxial with the axis of the cathode part and has a larger outer diameter than the outer diameter of the cylindrical protrusion is provided on the side facing the shield electrode, and the bottom surface of this cylindrical hollow part and the The shield electrode is configured so that the bottom surface of the cylindrical protrusion is in close contact with the bottom surface of the shield electrode, and a gap is maintained between the shield electrode and the insulator facing the shield electrode in a portion other than the contact portion. electron beam equipment.