JPH11213947A - Cathode for discharge tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharge tube having a long life and high output. SOLUTION: Porous tungsten is impregnated with an oxide containing at least Ba, a flat part 6 is formed at the tip of the porous tungsten, a hole 2 is formed in the center of the flat part 6 to form an impregnation type cathode 1, and the surface of the impregnation type cathode 1 except for the inside of the hole 2 is covered with a film 3 made of a high melting point metal or an alloy of the high melting point metal. By selecting the high melting point metal from tungsten, molybdenum, iridium, ruthenium, rhenium, and osmium, the tip of the cathode is durable to heat and displays good heat diffusing capability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge tube such as an arc discharge tube having a large load on a cathode, and more particularly to a cathode used for a high-power discharge tube of 500 W or more.

[0002]

2. Description of the Related Art In a discharge tube having a large load on a cathode, such as an arc discharge tube, an impregnated cathode or a thorium tungsten (Tr-W) cathode having a sharpened tip is used. For a discharge tube of 500 W or more, which is a discharge tube, a thorium tungsten cathode having high thermal stability is used. This is because in the impregnated cathode, the impregnating agent was remelted and spouted onto the surface layer, and the cathode was destroyed and could not be used.

As shown in FIG. 4, a thorium-tungsten cathode 5 is used by providing a flat portion 6 at a tip having a large heat load.

Nevertheless, since the electron emission ability of thorium tungsten is still low, the discharge voltage rises during discharge and heats the cathode more than necessary. As a result, the tip of the cathode is deformed in several hundred hours. As a result, the discharge characteristics deteriorate. That is, there is a problem that the life of the cathode is shortened when the output is increased.

An object of the present invention is to solve the above problems and extend the life of the cathode with a simple structure.

[0005]

In order to achieve the above object, a cathode for a discharge tube according to the present invention is a cathode for a discharge tube used for a high-output discharge tube having a flat portion at the tip. And an impregnated cathode obtained by impregnating porous tungsten with an oxide containing at least Ba having pores having openings in the flat portion, and a surface of the impregnated cathode excluding at least the inside of the pores. And a coating of a high melting point metal or an alloy of the high melting point metal applied.

The high melting point metal is suitable as any one of tungsten, molybdenum, iridium, ruthenium, rhenium and osmium.

In addition, the diameter of the flat portion is 500 W or more and 100
In a discharge tube of less than 0 W, 0.5 mm to 2 mm, 1 mm
In a discharge tube of 000 W or more, 1.0 mm to 5 mm
The size of the opening of the hole in the flat portion,
The discharge tube of 500 W or more and less than 1000 W has an area ratio of 10% to 70%, and the discharge tube of 1000 W or more has an area ratio of 10% to 90%.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. However, in a plurality of drawings, the same or corresponding components are denoted by the same reference numerals, and the description thereof will not be repeated.

FIG. 1 and FIG. 2 are views showing an embodiment of a cathode for a discharge tube according to the present invention, and show a front cross section and a flat portion plane, respectively. In the drawing, 1 is an impregnated cathode, 2 is a hole provided in the impregnated cathode 1, 3 is a coating applied to the impregnated cathode 1, 4 is a lead to which the impregnated cathode 1 is fixed, and a is a flat portion 6.
And b indicates the diameter of the hole 2.

The impregnated cathode 1 is formed by impregnating porous tungsten with an oxide containing at least Ba. The impregnated cathode 1 is formed in a truncated conical shape having a flattened tip as shown in FIG. A hole 2 is formed. The depth of the holes 2 needs to be formed in a range in which a temperature at which the electron emitting ability of the impregnating agent is sufficiently exerted at the time of discharge is given, and a depth of 1 mm or more is required to fill the gap. The holes may be made to penetrate the entire length of the cathode. Such an external shape can be formed by compression molding of tungsten powder performed before forming porous tungsten by sintering and its mechanical processing. The impregnating agent is generally used (Ba:
CaO: Al ₂ O ₃ ) = (4,1,1), (6,1,1)
2), (5, 3, 2) and the like can be adopted.

The coating 3 is formed by adding tungsten to the impregnated cathode 1.
It is formed by sputtering from 0 to 500 μm, and is formed over the surface excluding the inside of the hole 2. At the time of this sputtering, it is not necessary to particularly mask the holes 2, and even if the target material adheres to the inside of the holes 2, the amount is such that the electron emission is not affected.

The lead 4 is made of Mo or the like, and the impregnated cathode 1
And also serves as an extraction electrode to the outside,
An impregnated cathode 1 is fixed to the tip by fitting brazing or caulking.

Next, the operation of the cathode in this embodiment will be described below. First, when a high voltage is applied to the impregnated cathode 1 through the lead 4 to start discharging, the cathode temperature rises due to local self-heating at the tip, the electron emission capability is improved, and high current, low voltage operation is performed. In the state of arc discharge. By this heating, Ba diffuses on the porous tungsten crystal through the holes 2 and diffuses into the flat portion of the impregnated cathode 1. Thereby, the electron emission capability of the flat portion is further improved, and a stable discharge operation is performed.

The Ba diffused through the holes 2 as described above is adsorbed on the coating 3 adhered to the flat portion, and electrons are emitted from the portion to become a bright spot of discharge. This luminescent spot is in a range in which Ba diffuses from the opening of the hole 2 and spreads on the coating 3, that is, B
It is determined by the diffusion range of a.

In the conventional cathode, it is necessary to control the bright spot diameter by its tip angle, and when it is desired to reduce the bright spot diameter, it is necessary to reduce the tip angle. However, there was a problem that the tip was overheated. For this reason, high-power discharge tubes, etc., have a large tip angle,
Instead of dissipating heat, the design value is such that the bright spot diameter increases. However, in the present embodiment, since the bright spot diameter is determined by the diffusion range of Ba, the tip angle can be increased even when the bright spot diameter is reduced, and the thermal load on the cathode tip can be reduced. it can.

In the discharge tube cathode of the present invention, the tip of the impregnated cathode is greatly related to its output. When the tip has a conventional sharpened structure, the catastrophic breakdown may occur due to the above-mentioned thermal harm. Therefore, the present invention flattens the tip of the impregnated cathode to prevent thermal destruction of the cathode tip.

In the cathode of the present invention, the surface to which heat is most frequently input is covered with a sputtered film, so that the impregnating agent is prevented from being blown out of the surface, and necessary Ba is diffused from the inside, which does not reach a high temperature, through holes. Therefore, it has a more thermally stable structure. Since the flat portion provided at the tip of the cathode becomes a luminescent spot at the time of discharge and becomes a portion to receive heat input, it is necessary to secure a sufficient area to prevent the breakdown of the cathode. According to the experience and experiments of the inventors, a discharge tube having an output of 500 W or more has a flat portion diameter a of 0.5 mm to 2 mm, 1 mm or less.
The discharge tube of 000 W or more is set to 1.0 mm to 5 mm, and the size of the opening of the hole in the flat portion is determined by the area ratio (b / a) ×
100), it is 1 for a discharge tube with an output of 500 W or more.
It was suitable as 0% to 70% and 10% to 90% at 1000 W or more.

It should be noted that not only one hole is provided in the flat portion, but a plurality of holes may be provided as shown in FIG. Also in this case, it is desirable to satisfy the above-mentioned conditions of the flat portion diameter and the hole opening area ratio.

Although the embodiment has been described above, the present invention is not limited to this, and various modifications can be made. For example,
In the above embodiment, the coating applied to the surface of the impregnated cathode was made of tungsten (W). However, other high-melting metals, for example, molybdenum (M
o), iridium (Ir), ruthenium (Ru), rhenium (Re), osmium (Os), and the like. Further, among these high melting point alloys, those having a melting point sufficiently higher than the temperature at the time of operating the cathode, such as iridium-tungsten (Ir-W) and rhenium-tungsten (Re-W), may be used.

[0020]

As described above, the discharge tube cathode of the present invention uses an impregnated cathode in which holes are formed in the flat portion at the tip and a coating of a high melting point metal is provided on the surface thereof. A sufficient thermoelectron emission surface can be formed in the tube, and the heat load can be reduced by efficiently transmitting generated heat from the surface to the cathode body. Therefore, stable discharge characteristics can be obtained even in a high-power discharge tube.

In particular, when any of tungsten, molybdenum, iridium, ruthenium, rhenium and osmium is used as the refractory metal, it can withstand the heating of the cathode tip well and exhibit good heat dissipation.

The diameter of the flat portion is 0.5 mm to 2 mm for a discharge tube of 500 W or more, and 1.0 mm to 5 mm for a discharge tube of 1000 W or more, and the ratio of the opening area of the holes in the flat portion is 500 W to less than 1000 W. 10% to 70% for a discharge tube of 10% and 10% to 90% for a discharge tube of 1000 W or more, which is resistant to thermal destruction, withstands long-term discharge, and has a reliable and sufficient area of electron emission. Face can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a view showing a flat portion of the embodiment shown in FIG. 1;

FIG. 3 is a diagram showing another embodiment of the present invention.

FIG. 4 is a view showing one step of a method of manufacturing a semiconductor device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Impregnation type cathode 2 Void 3 Coating 4 Lead 5 Thorium tungsten cathode 6 Flat part

Claims (3)

[Claims] In a cathode for a discharge tube used for a high-power discharge tube, porous tungsten is impregnated with an oxide containing at least Ba having a flat portion at the tip and a hole having an opening in the flat portion. A cathode for a discharge tube, comprising: an impregnated cathode formed as described above; and a coating of a high-melting-point metal or an alloy of the high-melting-point metal applied to a surface of the impregnated-type cathode except for at least the inside of the pores. . 2. The cathode for a discharge tube according to claim 1, wherein the high melting point metal is any one of tungsten, molybdenum, iridium, ruthenium, rhenium, and osmium. 3. The flat part diameter is 500 W or more and 1000 W or more.
Less than 0.5 mm to 2 mm, 100
In a discharge tube of 0 W or more, the width is 1.0 mm to 5 mm, and the size of the opening of the hole in the flat portion is 10% to 70% in an area ratio of the discharge tube of 500 W or more and less than 1000 W, and 1000 W or more. 3. The discharge tube cathode according to claim 1, wherein the discharge tube has an area ratio of 10% to 90%.