JPH073771B2 - Static magnetic field superimposing electron gun - Google Patents

Description

The present invention relates to a thermionic emission type electron gun using a permanent magnet.

[Prior Art] Generally, there are an electron gun of a field emission type and a thermionic emission type, and a thermionic emission type electron gun heats a filament to radiate thermoelectrons, and a reverse bias is applied by a bias electrode. The beam current amount is controlled. An electric field is formed between the filament and the bias electrode to form a crossover of the electron beam emitted from the filament, which is regarded as a light source. When using this type of electrostatic lens,
Its characteristic is that it has a large aberration coefficient. Therefore, a magnetic field lens has been used instead of the electrostatic lens to improve the aberration coefficient. Generally, the use of a magnetic field lens has an effect that a sharp magnetic field can be obtained.

Luminance is one of the characteristics of the light source, but the ideal luminance value determined by the filament material actually deteriorates depending on the lens system used. That is, if the aberration coefficient is large, the ideal value of the brightness determined by the filament material is deteriorated.

Therefore, the magnetic field superposition type electron gun introduces a magnetic field lens having a small aberration coefficient to the lens action in the vicinity of the electron gun, which is conventionally formed only by an electrostatic lens, and reduces the aberration coefficient in the vicinity of the light source to reduce the electron gun. Various characteristics such as shown in FIG. 3 have been considered in order to improve the characteristics of (1) in the region where the probe diameter is large, that is, the angle of view of the light source is large. First, as shown in FIG. 3 (a), the lens portion formed by the coil 11 and the yoke 12 is provided in the low pressure portion outside the vacuum chamber 2, and as shown in FIG. 3 (b). It is known that a lens portion formed of the coil 11 and the anode 13 serving also as the yoke is provided in a high pressure portion in the vacuum chamber 2 in a state of being floated by an insulator 1 '.

[Problems to be solved by the invention]

However, although it is easy to manufacture a lens power source for the magnetic field superposition type electron gun shown in FIG. 3 (a), since the voltage is as high as 100 KV, the chamber diameter D of the electron gun must be sufficiently large to prevent discharge. However, there is a problem that the magnetic field is broad because the magnetic field is applied from a place with a certain distance. Therefore, as shown in FIG. 3B, a method of providing a magnetic field lens having a power source on the high voltage side near the light source is adopted. However, since this method has a lens near the filament,
Although the magnetic field is applied effectively, the power transmission transformer of the high-pressure tank (not shown) needs to have a large capacity in order to supply power to the lens because it is provided in the vacuum and high-voltage parts. However, there are problems in manufacturing such as the addition of a lens power source such as a stabilizer and an increase in the number of core wires of the high voltage cable, which complicates the processing of the terminal for inputting the lens power.

Therefore, it is an object of the present invention to provide an electron gun that effectively superimposes a magnetic field and can concentrate a strong magnetic field in the vicinity of a light source, like the magnetic field lens, and solves the above problems.

[Means for solving problems]

Therefore, the static magnetic field superposition type electron gun of the present invention has a thermionic emission type filament introduced into a vacuum chamber, a cylindrical bias electrode disposed in the vacuum chamber surrounding the thermionic emission type filament, A conductive ring-shaped magnetic body that is concentrically attached to the inner periphery of the end of the bias electrode and forms an opening, an anode that is arranged to face the thermionic emission type filament through the opening, and the ring-shape. A ring-shaped permanent magnet is provided on the anode side of the magnetic body so as to be concentric with the opening and gradually extend beyond the opening.

[Action]

By using a magnetic field lens made of a permanent magnet instead of the magnetic field lens made of an electromagnet, it is possible to solve the above-mentioned problems such as no need to provide a power source in the case of an electromagnet. Further, the surface facing the anode is in a high voltage state, and in the case of a sintered body such as a permanent magnet, the surface is rough, so that discharge is likely to occur. In the present invention, a problem such as electric discharge is solved by disposing a magnetic material, such as iron, which is easily surface-processed, on the surface facing the anode.

〔Example〕

 Embodiments will be described below with reference to the drawings.

FIG. 1 is a sectional view showing an electron gun section of the present invention, and FIG.
It is a figure which shows the magnetic flux intensity in each position on the optical axis of the electron gun part of this invention.

In the figure, 1 is an insulator, 2 is a chamber, 3 is an anode, 4 is an exhaust hole, 5 is an opening, 6 is a filament, 7 is a bias electrode, 8 is a magnetic material, 9 is a permanent magnet, and 10 is an opening. .

In the cylindrical vacuum chamber 2 exhausted through the exhaust hole 4,
A filament 6 connected to a filament power source and a lead wire connected to a bias power source are introduced from the upper surface of the chamber and insulated from the high voltage portion by the insulator 1. Then, a cylindrical bias electrode 7 is provided so as to surround the filament 6 and the end portion of the conductive wire connected to the bias power source.
, And the end of the lead wire connected to the bias power source is connected to the bias electrode 7. Further, the anode 3 having the opening 5 on the bottom surface of the vacuum chamber 2 is arranged so as to face the filament 6 to form a high-voltage portion.

Inside the other end of the bias electrode 7 attached to the insulator 1, a ring-shaped permanent magnet 9 is concentrically assembled with a ring-shaped magnetic body 8 having an opening 10 in the center, and attached. . As shown in FIG. 1, the ring-shaped magnet 9 is incorporated in the magnetic body 8 so as to be disposed on the anode 3 side, and the magnetic body 8 is incorporated in the vicinity of the opening 10. The ring-shaped magnetic body 8 is made of, for example, iron having conductivity, and the surface facing the anode 3 is preferably the anode 3
It is formed parallel to the surface and is extremely smooth to prevent discharge. The tip of the filament 6 is arranged so as to face the vicinity of the opening 10 of the ring-shaped magnetic body 8 so that a strong magnetic field is concentrated on the tip of the filament 6.

A magnetic field distribution chart formed by the electron gun thus formed is shown in FIG. The horizontal axis shows the distance on the optical axis from the tip of the opening 10 of the magnetic body 8, and the vertical axis shows the magnetic flux intensity at each position on the optical axis. As shown in FIG. 2, the magnetic flux is strongly concentrated near the tip of the opening 10 of the magnetic body 8.

The tip portion of the bias electrode 7 may be curved and extended to support the ring-shaped permanent magnet 9 portion.

〔The invention's effect〕

The present invention can solve the manufacturing problems in the case of the magnetic field lens by the electromagnet by adopting the magnetic field lens by the permanent magnet instead of the magnetic field lens by the conventional electromagnet,
In addition, it is possible to form an effect that a magnetic field lens with small aberration can be formed as in the case of the magnetic field lens in which the lens power source can be arranged near the filament. Also,
With the same beam diameter, there is also an effect that the beam capture angle can be increased.

[Brief description of drawings]

FIG. 1 is a sectional view showing an electron gun section of the present invention, and FIG.
FIG. 3 is a diagram showing the magnetic flux intensity at each position on the optical axis of the electron gun portion of the present invention, and FIG. 3 is a sectional view showing a conventional magnetic field superposition type electron gun portion. In the figure, 1 is an insulator, 2 is a chamber, 3 is an anode, 4 is an exhaust hole, 5 is an opening, 6 is a filament, 7 is a bias electrode, 8 is a magnetic material, 9 is a permanent magnet, 10 is an opening, 11 Is a coil, 12 is a yoke, and 13 is an anode that also serves as a yoke.

Claims (1)

[Claims] 1. A thermoelectron emission type filament introduced into a vacuum chamber, a cylindrical bias electrode disposed in the vacuum chamber surrounding the thermoelectron emission type filament, and concentric with an inner circumference of an end portion of the bias electrode. -Shaped conductive ring-shaped magnetic body that is attached in a circular shape and forms an opening, an anode that is arranged to face the thermionic emission type filament through the opening, and the opening on the anode side of the ring-shaped magnetic body. A static magnetic field superposition type electron gun including a ring-shaped permanent magnet that is concentrically incorporated with the opening except the portion.