JPH0568065U - Electron beam generator - Google Patents

Abstract

(57) [Abstract] [Purpose] It is an object to prevent the dielectric strength of an insulating spacer supporting a high-voltage conductor from being lowered by a magnetic field that suppresses the pinch effect of an electron beam. [Yusashi] A yoke is installed inside the high-voltage conductor, and the insulating spacer penetrates the yoke. A closed magnetic circuit is formed using this yoke. The magnetic field is not applied to the insulating spacer by passing the magnetic flux through the closed magnetic circuit.

Description

[Detailed description of the device]

[0001]

[Industrial application]

 The present invention relates to an electron beam generator.

[0002]

[Prior Art]

 In this type of electron beam generator, it is already known that an electron beam is generated by applying a high voltage pulse between a cathode and an anode arranged in a vacuum. FIG. 2 shows the conventional structure, 1 is a vacuum tank, 2 is an anode supported by a support conductor 3 provided in the tank 1, and 4 is a cathode supported by a high voltage conductor 5. Is.

The high-voltage conductor 5 is supported by a disk-shaped insulating spacer 7 attached to the tank 1. The outer end of the high-voltage conductor 5 penetrates the insulating spacer 7, and a high-voltage pulse from a high-voltage pulse power source 8 connected between the outer end of the high-voltage conductor 5 and the tank 1 causes the cathode 4 and the anode 2 to pass. The voltage is applied between them. An insulating medium is stored outside the insulating space 7.

When a high-voltage pulse is applied between the cathode 4 and the anode 2 as described above, electrons are field-emitted from the metal protrusions on the surface of the cathode 4, and the current causes the metal protrusions to be turned into plasma and cathode plasma to be generated. It is formed. A high-current electron beam is extracted by this plasma. For example, it is generally performed to extract an electron beam of several kA to several tens kA by applying a pulse voltage of several 100 kV to 100 ns.

In such a high-current electron beam, the pinch effect causes the beam to converge on the central part, which may make it impossible to obtain a beam having a large area and a uniform distribution. It becomes inconvenient for use such as irradiation. Therefore, conventionally, an electromagnet 10 is arranged outside the tank 1 to generate a longitudinal magnetic field (axial magnetic field) between the cathode 4 and the anode 2 so that the electron beam is forced to advance in the axial direction. I try to prevent a pinch. The dotted line shows the magnetic flux.

However, according to such a configuration, since the magnetic field is generated in the entire vacuum portion in the tank 1, the magnetic flux passes across the insulating space 7, and the creeping portion on the vacuum side has its axial direction and radial direction. It will be exposed to the magnetic field (direction toward the outer circumference). In this case, since the magnetic field in the radial direction is in the same direction as the electric field between the cathode 4 and the tank 1, it promotes vacuum creeping discharge on the creeping surface of the insulating spacer 7. As a result, the dielectric strength of the insulating spacer 7 is reduced.

Also, the axial magnetic field causes so-called E × B drift in the circumferential direction in the creeping portion, and secondary electron emission and the like due to electron collision with the creeping surface increases. This also reduces the dielectric strength of the insulating space 7.

[0008]

[Problems to be solved by the device]

 It is an object of the present invention to prevent a decrease in dielectric strength at a vacuum side creeping surface of an insulating spacer supporting a cathode even when a longitudinal magnetic field is formed in order to suppress a pinch effect of an electron beam.

[0009]

[Means for Solving the Problems]

 The present invention supports the first yoke and the anode inside the high-voltage conductor supporting the cathode, which is supported through the insulating spacer, so as to penetrate the insulating spacer. A second yoke is provided inside the support conductor, and a third yoke that magnetically bridges the first yoke and the second yoke is provided outside the tank. The yoke is characterized in that a closed magnetic circuit is formed and a permanent magnet is provided in the closed magnetic circuit.

[0010]

The anode and the cathode are positioned to face each other in the magnetic circuit, and the vertical magnetic field in the magnetic circuit suppresses the pinch effect of the electron beam. Since the first yoke is arranged so as to pass through the insulating spacer, there is almost no magnetic flux that intersects the insulating spacer, and therefore the magnetic field hardly acts on the vacuum side creeping portion. This prevents the dielectric strength of the insulating spacers from decreasing.

[0011]

【Example】

 An embodiment of the present invention will be described with reference to FIG. In addition, the same reference numerals as those in FIG. 2 indicate the same or corresponding portions. The high-voltage conductor 5 supported so as to pass through the insulating space 7 is hollow, and the first yoke 11 is arranged inside thereof. The yoke 11 also penetrates the insulating spacer 7, and the permanent magnet 12 is installed at the outer end thereof. The cathode 4 is supported on the tip of the high-voltage conductor 5.

The support conductor 3 that supports the anode 2 at the tip is also hollow, and the second yoke 13 is disposed inside the support conductor 3. A permanent magnet 14 is installed between the outer end of the yoke 13 and the tank 1.

A third yoke 15 is arranged outside the tank 1. The tip of the yoke 15 extends to the outside of the insulating spacer 7 and magnetically bridges the permanent magnet 12 and the permanent magnet 14. The yokes 11, 13 and 15 form a closed magnetic circuit. The anode 2 and the cathode 4 are located in this closed magnetic circuit, and the permanent magnets 12 and 14 are arranged.

In the above structure, the magnetic flux generated by the permanent magnets 12 and 14 passes through the closed magnetic circuit as shown by the dotted line. As a result, a vertical magnetic flux is generated between the anode 2 and the cathode 4, which suppresses the pinch effect of the electron beam. As a result, the electron beam can be uniformly generated and propagated in a large area.

On the other hand, since the outer end of the yoke 11 and the permanent magnet 12 are outside the insulating spacer 7, the magnetic flux passing between the yoke 15 and the yoke 11 rarely crosses the insulating space 7. .. Even if there is some leakage flux, it is extremely small compared to the conventional example. As a result, the creeping surface of the insulating space 7 on the vacuum side is not adversely affected by the application of the magnetic field, and the original high dielectric strength can be maintained.

The yoke 15 in the illustrated example is arranged so as to surround the entire tank 1 and is axisymmetric, but if the cross-sectional area is such that it is not magnetically saturated, it is asymmetrical. May be.

[0017]

[Effect of the device]

 As described above, according to the present invention, when suppressing the pinch effect of the electron beam by the magnetic field, it is avoided that the insulating spacer supporting the high voltage conductor impairs the dielectric strength due to the magnetic field. It has the effect of maintaining dielectric strength.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a sectional view of a conventional example.

[Explanation of symbols]

 1 Tank 2 Anode 3 Support Conductor 4 Cathode 5 High Voltage Conductor 7 Insulating Spacer 8 High Voltage Pulse Power Supply 9 Electron Beam 11 First Yoke 12 Permanent Magnet 13 Second Yoke 14 Permanent Magnet 15 Third Yoke

Claims (1)

[Scope of utility model registration request] 1. A vacuum tank is provided with a cathode supported by a high voltage conductor and an anode supported by a support conductor, and a high voltage pulse is applied between the cathode and the anode. An electron beam generator for generating an electron beam by means of supporting the high-voltage conductor through an insulating spacer supported by the tank, and penetrating the insulating spacer inside the high-voltage conductor. A second yoke inside the support conductor, and a third yoke magnetically bridging the first yoke and the second yoke outside the tank. And a permanent magnet is provided in the closed magnetic circuit, the closed magnetic circuit is formed by the first to third yokes.