JPS60157148A - Electron generator unit - Google Patents

Abstract

PURPOSE:To reduce discharge holding voltage by forming a gap that is connected to the inner part of an electron emission body between the partial circumference surface of a pipe type electron emission body and the electron emission body holding tool in a hollow cathode type electron generation unit. CONSTITUTION:A cathode disk 4 is arranged so as to be opposed to a keeper electrode 1 and airtightly connected to a cathode pipe 3. Besides, a hollow cathode type electron generation unit is formed by providing a pipe type electron emission body 6 held in the pipe 3 with a holding tool 10 and then a heating heater 7. In this case, the holding tool 10 uses a holding tool 101 so that a gap can be formed by providing a step section (A) on the circumferential surface of the electron emission body 6, and the plasma 12 generated in the cathode pipe 3 can flow in the gap. As a result, since the circumferential surface of the electron emission body 6 can also be used as the electron emission surface, the emission electron amount can be increased and the discharge holding voltage and power consumption can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron generating device that uses a hollow discharge cathode to increase the efficiency of gas discharge and extracts electrons through the discharge.

Conventionally, as a device that generates electrons, temperatures of 1000℃~
Thermionic cathodes, which utilize thermionic emission from a cathode heated to 2500°C, are most commonly used. This is because the configuration is simple and the operation is reliable.

In addition, a field emission type electron gun is sometimes used to obtain a narrow and well-focused electron beam. Electron guns that use gas discharge are also called plasma electron guns.

Although it is not a high-quality electron beam in terms of electron energy uniformity and convergence, it is possible to obtain a high-density electron beam, so it can be used to heat and melt materials using an electron beam, and as an electron source in an ion source device. In addition, it is often used for purposes that require a large current, although the quality of the beam does not matter much.

A hollow cathode is a type of electron source that uses gas discharge, and the cathode part is made hollow with a pipe etc.
This is an electron source with improved thermal efficiency.

In addition, part or all of the cathode pipe is made of a material with a low work function.
Structures made of so-called electron-emitting materials to further improve efficiency are also frequently used. Furthermore, for the same reason, a structure in which an electron-emitting material is inserted into the cathode pipe is also used. FIG. 1 shows a schematic structure of the main parts of a conventional hollow cathode type electron generator. In the figure, (1) is a discharge sustaining anode plate, also called a keeper electrode (
There is an electron extraction hole (2) in the center (hereinafter referred to as keeper electrode), 4 (3) is a cathode pipe, (4) is a cathode disk hermetically sealed to the cathode pipe (3), and the keeper electrode ( 1)
A fine hole (5) was drilled in the husband while he was facing her. This fine hole (5) is arranged approximately coaxially with the electron extraction hole (2) of the keeper electrode (1). (6) is a pipe-shaped electron emitter, which is held on the cathode pipe (3) by a holder aO.

Further, the holder αO is fixed to the cathode pipe (3) by a suitable support (11). (7) is a heater for heating the cathode, and is insulated and held by a heat-resistant insulating layer (8) such as an ARv.

Next, referring to FIG. 2, the operation of the conventional hollow cathode type electron generator will be described. To start up the hollow cathode, a discharge forming gas (9) is first introduced from the cathode pipe (3). This gas flows towards the keeper electrode (1) through the micrometering orifice (5) of the cathode disk (4). Next, a current is passed through the cathode heater (7) to heat the cathode pipe (3) and cathode disk (4), and at the same time apply a positive escape pressure of several hundred volts to the keeper electrode (1). When the temperature reaches around 1000°C, gas discharge occurs between the negative disc (4) and the keeper electrode (1) due to thermionic electrons generated from the cathode disc (4). Since the hot electrons only act as a trigger for the start of discharge, an electron flow of about microamperes is sufficient.After the start of discharge, the pipe-shaped electron emitter (6) and the keeper The current is now maintained between the electrodes (1), and even if the cathode heater (7) is no longer energized, the discharge is maintained between the electrodes (1). 1) The applied voltage is 10~
decreases to aOV. On the other hand, since the voltage of the keeper electrode (1) is positive, electrons flow toward the keeper electrode (1), and most of them flow into the keeper electrode (1).
A portion is emitted to the outside through the electron extraction hole (2) in the center of the keeper electrode.

Next, the mechanism for maintaining the discharge of the hollow cathode will be explained with reference to Fig. 2. In the figure, the a force is plasma.

Generally, in a sustained discharge space, most of the space is usually composed of plasma. It is known that in plasma, the electron density and ion density are almost equal, and the electric field is close to zero. However, near the cathode, the electric field disturbs the equilibrium condition between electron density and ion density, and the ion density increases. In addition, since the boundary between this equilibrium part and the non-equilibrium part is usually quite clear, this boundary surface is a plasma boundary surface,
The area between the plasma interface and the cathode is called the ion sheath, and it is known that most of the discharge sustaining voltage is applied to the ion sheath. The thickness of this ion sheath can be approximately expressed as λn-(EoMTe/e Ine) ''.Here, the entrance is the thickness of the ion sheath, %EO is the dielectric constant, K is the Boltzmann coefficient, and Te is the electron temperature, e is the electron charge, and n6 is the electron density.

Now, if the condition of 2λD<<J is satisfied, the plasma formed by the discharge between the cathode disk (4) and the keeper electrode (1) will pass through the micropores (5) of the cathode disk (4). It can enter the cathode pipe (3) and reach the inner cylinder of the pipe-shaped electron emitter (6). Here, Di is the diameter of the micropore (5). On the inner surface of the pipe-shaped electron emitter (6), 2
Secondary electrons are emitted, but because the work function of the surface is low and the pipe-shaped electron emitter (6) is almost confined by the cathode pipe (3) and cathode disk (4), the ions The combination of conditions such as high efficiency of heating by impact leads to active electron emission. As a result, the discharge sustaining voltage decreases, and the discharge continues even if the power supply to the cathode heater is stopped.

Now, the discharge sustaining voltage is one of the important characteristic values of the hollow cathode, and by keeping this voltage low, not only the power consumption is reduced, but also the ion energy is reduced, which causes damage to the cathode surface due to ion bombardment. becomes less,
The life of the hollow cathode can be extended.

An electron generating device using a hollow cathode constructed in this manner has a low keeper voltage, that is, a discharge sustaining voltage, and thus has low power consumption and a considerably long life. However, when this hollow cathode type electron generator is used, for example, in an ion engine as a space propulsion engine, it is often not sufficient in terms of power consumption and service life, and the discharge maintenance voltage is needed to be lowered even further. For this reason, the inventors first
The pipe-shaped electron emitter (6) and the cathode disk (
It was announced that the discharge sustaining voltage can be lowered by arranging the electrodes 4) with a gap of, for example, α3N, instead of placing them in close contact with each other.

The present invention is a further development of this.

By devising the shape near the pipe-shaped electron emitter,
Furthermore, it is an object of the present invention to provide an electron generator with improved discharge sustaining voltage characteristics, long life, and low power consumption.

Hereinafter, one embodiment of the present invention will be described based on FIG. 3.

In the figure, (101) is an improved holder,
It is held on the outer peripheral surface of the pipe-shaped electron emitter (6). Further, a stepped portion A is provided on the inner surface of the tip portion of the holder (101) so as to create a gap on the outer circumferential surface of the pipe-shaped electron emitter (6). For other components, please refer to Section 1.
It is similar to the figure.

In the hollow cathode type Y electron generating device according to the present invention configured in this way, the thickness of the ion sheath is the same as in the prior art.
) is smaller than the gap between the outer peripheral surface of the holder (101') and the inner surface of the holder (101'), it is thought that the plasma in the cathode vibe will enter into the gap.

As a result, the area where the plasma and the electron emitter face each other increases, the amount of emitted electrons increases, and the discharge sustaining voltage decreases.

The present invention is devised so that the outer circumferential surface of the pipe-shaped electron emitter can also be used as an electron emitting surface.

In the description of one embodiment of the present invention, a step is provided on the inner surface of the holder, but it goes without saying that even if a step is provided on the outer circumferential surface of the pipe-shaped electron emitter (6), the same or similar effective. In addition, the pipe-shaped electron emitter (6) is held only on the upstream side of the electron flow, so that the pipe-shaped electron emitter (6)
A gap may be created directly between the cathode pipe (3) and the cathode pipe (3).

As described above, in the present invention, the outer peripheral surface of the pipe-shaped "zeon emitter" is used as an electron emitting surface, so that the discharge sustaining voltage is reduced, and as a result, power consumption is reduced. Since the ion energy is lowered, the damage to the cathode surface due to ion bombardment is reduced, and the life of the hollow cathode can be extended.

Furthermore, since the enlargement of the electron emitting surface means that the current density on the electron emitting surface is reduced, the life characteristics can also be improved as a result.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the main part of a conventional device, FIG. 2 is an explanatory diagram of its operation, and FIG. 3 is a sectional view of the main part of a device according to an embodiment of the present invention. (1)...Keeper electrode, (2)...Electron emission window,
(3)... Cathode pipe, (4)... Cathode disk, (5
)...Micropore, (6)...Pipe-shaped electron emitter, (
7)...Cathode heater, (8)...Insulating layer (9)
...Gas, 01...Holder, (1013...Holder % (11)...Support, 0■...Plasma In addition, the same symbols in the figure indicate the space or corresponding part, respectively. . Agent Masuo Oiwa

Claims (2)

[Claims] (1) A keeper electrode that has an electron emission hole in the center and acts as an anode for sustaining the discharge, a cathode pipe that faces the keeper electrode and is placed approximately coaxially with the electron emission hole, and this cathode. A cathode disk that is hermetically sealed to the pipe and has a fine hole in the center, a pipe-shaped electron emitter inserted into the above cathode pipe near the cathode disk, and a pipe-shaped electron emitter that holds the pipe. a holder, and a mechanism capable of supplying discharge forming gas into the cathode pipe, between the cathode part composed of the corner plate disk and the pipe-shaped electron emitter and the keeper electrode. , in a hollow cathode type electron generating device configured to draw out electrons from the electron emitting hole by forming a sustained gas discharge, the outer circumferential surface of at least a part of the pipe-shaped electron emitting body and the holder; Between,
An electron generating device characterized in that a gap communicating with the inside of the pipe-shaped electron emitter is formed. (2) The electron generating device according to claim 1, wherein the gap is formed on the side near the cathode disk of the pipe-shaped electron emitter.