JPH01309241A - Hollow cathode - Google Patents

Abstract

PURPOSE:To make it possible to maintain the discharge securely even though the gas flow is little and to reduce the drawing-out voltage of electrons by providing a gas pressure increasing device opposing to a cathode disk. CONSTITUTION:Between the first keeper electrode 5 and a keeper cover 7, the second keeper electrode 10 is provided, and an anode as a gas pressure increasing device is composed of the second keeper electrode 10 and the first keeper electrode 5. As a result, a part of the gas flow passing through the first keeper electrode 5 strikes the second keeper electrode 10, and the gas pressure is raised not only near the second keeper electrode 10, but also near the first keeper electrode 5. Consequently, the gas is utilized effectively, the stability of discharge is improved even when the gas flow is little, and the cathode lowered voltage of discharge is lowered by the increase of the gas pressure to reduce the drawing-out voltage of the electron flow.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a hollow cathode that generates a high-density electron flow by gas discharge.

[Conventional technology]

FIG. 3 is a partial cross-sectional view showing a conventional hollow cathode. In the figure, 1 is a discharge forming gas for forming a gas discharge, 2 is a cathode pipe that guides this discharge forming gas 1, and 3 is an electron emissive material. A discharge cathode made of metal, which is installed along a part of the inner peripheral surface of the cathode pipe. This discharge cathode 3 is heated by the ion city 5, and since the higher the temperature, the easier it is to emit electrons, it has a heat-retaining structure. Reference numeral 4 denotes a cathode disk having a fine hole in the center serving as a gas and electron ejection hole 4a, which is hermetically sealed to one end of the cathode pipe 2. 5
is a keeper electrode having an orifice 5a facing the cathode disk 4 and serving as an anode for forming a discharge, and has a heat shielding effect. 6 is a keeper support that forms an appropriate gap between the keeper electrode 5 and the cathode disk 4; 7 is a keeper cover that holds the thinly formed keeper electrode 5 on the keeper support 6; and 8 is a keeper cover that maintains the keeper potential from the cathode. The insulated pipe 9 for floating is a collector into which some of the electrons in the discharge plasma flow, and the collector 9 does not necessarily have to be a tangible electrode, for example, a hollow cathode for the purpose of neutralizing the intermediate charge of the ion beam. When emitting electrons from an ion beam, the ion beam becomes the collector. Further, a heating means is provided for the discharge cathode 3 and the cathode disk 4 to facilitate the start of discharge, but the heating means is omitted for the sake of simplicity.

Next, the operation will be explained. When the discharge forming gas 1 is flowed into the cathode pipe 2 and a positive voltage is applied to the keeper electrode 5, a gas discharge is formed between the keeper electrode 8i5, the cathode disk 4, and the discharge cathode 3. When a gas discharge is formed, some of the electrons in the discharge plasma flow into the keeper electrode 5 and the other part flow into the collector 9.

Although the electron flow extracted from the hollow cathode does not have good beam quality in terms of energy distribution or focusing, a high-density electron flow can be obtained because the space charge of the electrons is relaxed by the plasma.

Now, the mission of the hollow cathode is to draw out the electron flow to the outside of the keeper electrode 5, so the electron flow flowing into the keeper electrode 5 becomes a reactive current, that is, a loss, but unless a certain amount of current flows, a stable discharge can be maintained. I can't.

Since the ejection holes 4a of the cathode disk 4 are minute holes, the gas flow becomes a jet flow downstream of the cathode disk 4, and the gas flow becomes a jet flow.
In the vicinity of , the pressure distribution is biased towards the central axis (Fig.
a), see Figure 4(b)). Since the keeper electrode 5 is an anode that maintains discharge, the vicinity of the non-porous portion of the keeper electrode 5 must also have an appropriate gas pressure. However, in order to increase the gas pressure in the non-porous part (periphery) of the keeper electrode 5, it is necessary to increase the gap between the cathode disk 4 and the keeper electrode 5.
Alternatively, it is necessary to make the orifice 5a of the keeper electrode 5 smaller, but if the gap is made larger, not only will the electric field decrease even at the same voltage (keeper voltage), but the positive column will become longer and the potential will drop within the positive column. In this case, the keeper voltage increases. On the other hand, if the diameter of the orifice 5a of the keeper electrode 5 is made smaller, the current density becomes higher for the same extraction electron current (collector current), leading to an increase in the extraction voltage. There was a limit to the improvement of characteristics by adjusting the gap alone.

(Problems to be Solved by the Invention) Since the conventional hollow cathode is configured as described above, the collector voltage may not be lowered sufficiently by adjusting the position of the keeper electrode or the orifice diameter of the keeper electrode, or the gas flow rate may There have been problems such as not being able to sustain the discharge stably when the discharge is small.

This invention was made to solve the above-mentioned problems, and it is a hollow cathode that can maintain stable discharge even when the gas flow rate is low, and can sufficiently extract electrons even when the electron extraction voltage is low. The purpose is to obtain.

[Means to solve the problem]

The hollow cathode according to the present invention is provided with gas pressure increasing means facing the cathode disk for substantially increasing the depth of the orifice of the anode so as to increase the gas pressure around the anode.

(Function) In the hollow cathode of the present invention, by providing the gas pressure increasing means opposite to the cathode disk, the gas pressure near the keeper electrode is increased, and the discharge is reliably maintained even when the gas flow rate is low. , and the electron extraction voltage can also be lowered.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a sectional view showing an embodiment of the present invention. In FIG. 1, the same or equivalent components as in FIG. 3 are designated by the same reference numerals, and redundant explanation will be omitted. In FIG. 1, 10 is a second keeper electrode provided between the first keeper electrode 5 and the keeper cover 7;
The keeper electrode 5 constitutes an anode as a gas pressure increasing means. Also, the orifice 10a of the second keeper electrode 10
The diameter of is 1 to the diameter of the orifice 5a of the first keeper electrode 5.
It is formed 1.5 times larger. 11 is the first keeper electrode 5
and the second keeper electrode 10.

Next, the operation of this embodiment will be explained. In this embodiment, since the anode is constituted by the first keeper electrode 5 and the second keeper electrode 10, a part of the gas flow that has passed through the first keeper cover 5 collides with the second keeper electrode 10. death,
The gas pressure not only near the second keeper electrode 10 but also near the first keeper electrode 5 increases. As a result, the gas is used effectively, and the stability of the discharge is improved even when the gas flow rate is small.In addition, due to the increase in gas pressure, the cathode drop voltage of the discharge is reduced, resulting in the extraction voltage of the electron flow ( collector voltage) decreases.

In the above embodiment, the second keeper electrode 10 is provided, the first keeper electrode 5 and the second keeper electrode 10 constitute an anode, and the gas pressure is increased to substantially increase the orifice depth of the anode. As shown in FIG. 2, an expansion tube 12 is connected to the orifice 5a of one keeper electrode 5.
Even if the anode is constituted by the keeper electrode 5 and the expansion tube 12, the same effects as in the above embodiment can be obtained. In addition, the expansion tube 12
Instead, it may be a straight tube, and the orifice 5
If the depth of a is formed to be about 0.5 to 2.0 times the orifice diameter, the same effect as in the above embodiment can be obtained.

Further, in the above embodiment, a gas pressure increasing means is provided which constitutes an anode by the first keeper electrode 5 and the second keeper electrode 1o and substantially deepens the orifice depth of the anode. As a means, even if the orifice diameter of the keeper cover 7 is made smaller, the same effect as in the above embodiment can be obtained.

(Effects of the Invention) As described above, according to the present invention, since the second keeper electrode is provided, the stable sustainability of the discharge is improved even when the gas flow rate is small, and the extraction voltage of the electron flow is also reduced. This effect can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the present low cathode according to an embodiment of the present invention, FIG. 2 is a sectional view of a hollow cathode showing another embodiment of the invention, and FIG. 3 is an example of a conventional hollow cathode. The cross-sectional view and FIG. 4 are explanatory diagrams showing the flow of gas near the keeper electrode. 2 is a cathode pipe, 3 is a discharge electrode, 4 is a cathode disk, 4a is an ejection hole, 5 is a first keeper electrode, and 10 is a second keeper electrode as a gas pressure increasing means. In addition, in the figures, the same reference numerals indicate the same or corresponding parts. Patent Applicant Mitsuru Electric Co., Ltd. Agent Patent Attorney 1) Hiroshi Sawa 1989-(2 others) 2nd rI! J (a)

Claims (1)

[Claims] A discharge cathode provided along the inner circumferential surface of a cathode pipe that guides discharge forming gas, a cathode disk joined to one end of the cathode pipe and having a gas and electron ejection hole in the center, and this cathode circle. In a hollow cathode comprising an anode having an orifice substantially coaxially with the plate, gas pressure increasing means is provided to substantially increase the depth of the orifice of the anode so as to increase the gas pressure around the anode. A hollow cathode characterized by: