JPH0473896A - Plasma generating device - Google Patents

Abstract

PURPOSE:To efficiently generate a spatially uniform and stable plasma by providing an anode having a number of holes formed therein to surround a first cathode, and providing a second cathode to surround the anode. CONSTITUTION:An anode 2 having a number of holes is provided to surround a filament 1, and a cylindrical cathode 3 is provided to surround the anode 2. Thus, thermions repeat reciprocating motion through the holes of the anode 2 in a space regulated by the filament 1 and the cathode 3, whereby the operating gas injected through an injection pipe 9 is reacted with the thermions and electrolyzed to form ions, forming a plasma. Thus, a spatially uniform and stable plasma can be efficiently generated with a small power source capacity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a plasma generation device that generates highly ionized, high-density plasma.

[Prior Art] As a plasma generation device, a device is known that generates plasma by ionizing a working gas with electrons (thermoelectrons) having sufficient kinetic energy.

In this case, in order to increase the ionization efficiency in the working gas, it is necessary to increase the effective flight length of the thermoelectrons in the working gas.

By the way, as methods for increasing the effective flight length of thermoelectrons, there are (a) a method using an electric field and a magnetic field, and (b) a method using only an electric field.

In the plasma generator using an electromagnetic field (a), a driving force in the cross product direction of an electric field and a magnetic field is applied to thermoelectrons in an operating gas atmosphere to cause the thermoelectrons to move in a trochoidal manner. This causes the working gas to undergo direct current discharge within the electromagnetic field, turning it into plasma.

However, in the plasma generating device (a) that uses an electromagnetic field, plasma can be generated efficiently by the electromagnetic field, but since a magnetic field is used, the plasma density becomes non-uniform, and furthermore, due to the effects of the electric and magnetic fields, plasma can be generated efficiently. However, the drawback is that the plasma drifts and noise is generated.

Next, a plasma generating apparatus using only an electric field (b) will be explained with reference to FIG. 6.

This type of plasma generator has a filament 1 (first
a cathode), an anode 2 provided near the filament 1 and kept at a positive potential, and a cathode 3 (second cathode) provided at a position facing the anode 2 and kept at the same potential as the filament 1. It is equipped with Note that the anode 2 has mesh-like holes.

In use, first, the inside of the vacuum container (not shown) is evacuated. A working gas to be turned into plasma is injected into a vacuum container. A voltage is applied between the anode 2 and the cathode 3 to create an electric field, causing the hot electrons from the filament 1 to move within the electric field. That is, within the vacuum container, the thermoelectrons emitted from the filament 1 move back and forth (vibrate) through the holes in the anode 2 within a space defined by the filament 1 and the cathode 3. At this time, the thermoelectrons collide with the working gas to ionize the working gas and turn it into plasma.

[Problems to be Solved by the Invention] However, in this type of plasma generator, each electrode faces each other, so the plasma generated between each electrode becomes spatially non-uniform, and becomes unstable. The drawback was that the generation efficiency was not good.

Therefore, a technical object of the present invention is to provide a plasma generation device that generates spatially uniform, stable, and efficient plasma.

[Means for Solving the Problems] According to the present invention, a first cathode that emits thermoelectrons;
an anode installed at a distance from the first cathode, and a second cathode installed at a distance from the anode, defined by the first cathode and the second cathode. In a plasma generation device that vibrates the thermoelectrons in space and generates plasma by interaction between the thermoelectrons and a working gas, the anode is disposed so as to surround the first cathode, and the anode is arranged so as to surround the anode. A plasma generating device characterized in that the second cathode is provided is obtained.

[Example] Hereinafter, a plasma generator according to an example of the present invention will be described with reference to the drawings.

Referring to FIGS. 1 and 2, the plasma generation device according to the present invention includes a filament 1 (cathode of ji!1) that emits thermoelectrons when heated, and a cylindrical anode 2 surrounding the filament 1. and a cylindrical cathode 3 (second cathode) surrounding the anode 2. These filament 1, anode 2, and cathode 3 are housed in a vacuum container 10. What is filament 1 and cathode 3?
The anode 2 is kept at the same negative potential, and the anode 2 is kept at a positive potential. The vacuum container 10 is provided with lead terminals 6.7 and 8, and the filament 1, anode 2, and cathode 3 are connected to a filament power source 4 and a discharge power source via the lead terminals 6.7 and 8 as shown in the figure. 5. Further, the vacuum container 10 is provided with an injection tube 9. The injection tube 9 is used when injecting the working gas to be turned into plasma into the vacuum container 10 .

Note that the cylindrical anode 2 has a large number of holes formed in a mesh shape, and these holes are formed in, for example, a slit shape or a grid shape.

In use, first, the inside of the vacuum container 10 is evacuated to a high vacuum (for example, 10-' Torr or less). Thereafter, the pressure of the working gas is injected into the vacuum container 10 through the injection pipe 9, so that the pressure inside the vacuum container 10 is 5×10 −5 to I×1.
0-2 Torr. Then, a discharge (DC) voltage of 110 V is applied from the anode power source 5 between the anode 2 and the cathode 3 to cause a discharge current of 30 A to flow, while a filament voltage of 35 V is applied from the filament power source 4 to flow a filament current of 30 A to cause the filament to Heat 1. Thermionic electrons emitted from the filament 1 fly out radially toward the anode 2, pass through the holes in the anode 2, and approach the cathode 3. And the thermionic electrons are at the cathode 3
It is repelled by the air, and then reverses and heads towards the anode 2. In this way, the thermoelectrons repeatedly move back and forth through the holes in the anode 2 within the space defined by the filament 1 and the cathode 3, so that the working gas injected from the injection tube 9 interacts with these thermoelectrons. Then, it is ionized and becomes ions, forming a plasma.

Referring to FIG. 3, when comparing the conventional example and the embodiment of the present invention, it is found that in the embodiment of the present invention, the electron temperature is higher than before and high-density plasma is generated even at a lower discharge voltage than before. I know what I can do.

With this configuration of the present invention, the efficiency of generating plasma is improved compared to the conventional method, and the operating gas pressure can be increased by up to 5x.
It becomes possible to generate a discharge even in a high vacuum of 10-' Torr.

Although cylindrical anodes and cathodes were used in the embodiments described above, anodes and cathodes such as those shown in FIGS. 4(a), (b), and (C) may also be used.

Fig. 4(a) shows a triangular cylindrical anode and cathode, Fig. 4(b) shows a square cylindrical anode and cathode, and the fourth
In Figure (C), an octagonal cylindrical anode and cathode are used. In any case, a cylindrical anode may be arranged to surround the filament, and a cylindrical cathode may be arranged around this anode. Alternatively, semicylindrical anodes and cathodes may be used as shown in FIGS. 5(a) and 5(b).

[Effects of the Invention] As explained above, according to the present invention, an anode having a plurality of holes is provided to surround a first cathode, and a cylindrical second cathode is further provided to surround this anode. Because of this provision, thermoelectrons can be confined in the space defined by the first cathode and the second cathode. As a result, there is an effect that plasma can be generated spatially uniformly, stably, and efficiently with a small power supply capacity.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a plasma generator according to an embodiment of the present invention;
2 is a cross-sectional view of the main part taken along line AA in FIG. 1, FIG. 3 is a comparison diagram between the conventional example and the embodiment of the present invention, and FIG.
Figures (a), (b), and (c) show other embodiments of Figure 2, and Figures 5 (a) and (b) show still other embodiments of Figure 2. FIG. 1 and FIG. 6 are diagrams showing a conventional plasma generation device. 1... Filament (first cathode), 2... Anode, 3... Cathode (second cathode), 4...
・Filament power source, 5...Discharge power source, 6.7.8・
...Lead terminal, 9...Injection tube, 10...Vacuum container. Figure 1 Figure 2 Figure 3 Figure 4 (CL)

Claims (1)

[Claims] (1) comprising a first cathode that emits thermoelectrons, an anode installed at a distance from the first cathode, and a second cathode installed at a distance from the anode,
In the plasma generation device, the anode vibrates the thermionic electrons in a space defined by the first cathode and the second cathode, and generates plasma by the interaction between the thermionic electrons and the working gas. A plasma generating device characterized in that the second cathode is arranged so as to surround the first cathode, and the second cathode is arranged so as to surround the anode.