JPH08250782A - Impregnated cathode body structure - Google Patents

Abstract

PURPOSE: To improve the service life and reliability of an impregnated cathode body structure used for the discharge tube of an Ar ion laser tube, etc., by preventing the deformation and short-circuiting of a cathode when the cathode is heated and reducing the current density and lowering the operating temperature by increasing the surface area. CONSTITUTION: An impregnated cathode body structure 5 is constituted by burying a heater 2 in the substrate 1 of an impregnated cathode composed of porous tungsten having a porosity of 20% as a heating source with an alumina insulator 3 and impregnating the body structure 5 with an oxide 4 having a composition of 4BaO, CaO, Al2 O3 by melting the oxide 4 in a hydrogen atmosphere.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an Ar ion laser tube, K
The present invention relates to an impregnated cathode assembly for a discharge tube such as an r-ion laser tube, and more particularly to a cylindrical impregnated cathode assembly capable of obtaining a high current density and having a long life and high reliability.

[0002]

2. Description of the Related Art A cathode structure used for an Ar ion laser tube requires a high current density.
HEATED TUNGSTEN DISPENSER CATHODES FOR ION LASER
An impregnated cathode structure having the structure discussed in "APPLICATION" (LASER JOURNAL NOV / DEC '1969) is used.

FIG. 4 shows Ar having an example of a conventional cathode structure.
FIG. 5 shows a schematic structure of an ion laser tube, and FIG. 5 shows a structure of a conventional impregnated cathode structure.

The Ar ion laser tube shown in FIG. 4 has a spiral shape made of tungsten and has an outer diameter of 13 mm and an inner diameter of 10 mm.
By the discharge generated by applying a high voltage through a thin tube 8 made of an insulating material between the impregnated cathode 6 and the anode 7 made of copper and having a pipe shape with a central portion passing through and an outer diameter of 10 mm and an inner diameter of 2 mm. Ar gas is ionized and a laser output is generated by its population inversion and optical resonance. If the output direction is blocked by the cathode 6 in this optical resonance system, optical resonance occurs and a laser output 9 cannot be obtained. Therefore, as shown in FIG. An impregnated cathode assembly 11 is used. The laser output 9 is taken out through a central portion 10 of the impregnated cathode structure 11 shown in FIG.

[0005] An impregnated cathode assembly 11 shown in FIG. 5 is made of an oxide containing barium in pores of a heat-resistant porous metal base 12 made of tungsten, usually BaO, CaO, Al ₂ O _2.
Is a substrate having a structure impregnated with a compound 13 consisting of A
The impregnated cathode assembly 11 used in the r-ion laser tube is constructed by applying an electric current directly to the tungsten, which is the base metal, to produce about 1100
It is a direct heating type cathode that heats up to ℃ and emits thermoelectrons.The cathode structure is exposed to the plasma atmosphere and the cathode structure has a spiral shape. A large temperature gradient occurs at. Due to this temperature gradient, there is a problem that the base metal is deformed during the operation of the Ar ion laser tube, the wire is disconnected or short-circuited, and the plasma discharge is stopped. Was expanded to 1 mm or more to prevent the plasma discharge from stopping due to deformation.

As described above, in the conventional structure, it is necessary to widen the winding pitch of the spiral shape to 1 mm or more.
It is impossible to increase the surface area of the cathode structure that effectively contributes to maintain the above-mentioned large-current plasma discharge. The lower the current density of the impregnated cathode, the lower the operating temperature. Therefore, it is essential to increase the surface area of the cathode structure in order to prolong the life and increase the current. According to the experimental results, if the current density is reduced to 1/2, the operating temperature of the cathode becomes 3
It has been found that the temperature can be lowered by 0 ° C., and the life is extended twice by this temperature reduction.

As a hollow cathode assembly, for example, Japanese Patent Application Laid-Open No. 1-187747 discloses a technique of hollowing the cathode assembly in order to prevent the cathode from being damaged by ion bombardment as shown in FIG. . This avoids and prevents ion bombardment damage of gas molecules ionized by electron collision in a low vacuum. A hollow 15 is provided in the center of the cathode 14 and electrons 18 focused by the Wehnelt electrode 16 and the anode 17 collide with gas molecules, and ionized gas ions collide with the center of the cathode by the electric field between the Wehnelt electrode 16 and the anode 17. . A hollow structure is used to prevent damage to the cathode due to the collision. In addition, the surface of the hollow 15 of the cathode 14 is a smooth surface without undulations, and the heating filament is provided separately from the cathode assembly 14.

On the other hand, the hollow structure of the cathode structure of the Ar ion laser, which is always exposed to ion bombard in a plasma atmosphere, maintains optical resonance, and has a completely different purpose from the hollow structure for avoiding ion bombardment. Become
In the Ar ion laser tube, ion bombardment is always generated by plasma discharge, and the electron beam generated by the anode 17 and the Wehnelt electrode 16 is not focused by the electric field as shown in FIG. 6, so the ion bombardment is concentrated on the center of the cathode surface. There is no such thing. Therefore, ion bombardment cannot be avoided by using a central structure in an Ar ion laser tube.

Further, Japanese Unexamined Patent Publication No. 2-162633 discloses a technique in which a hollow cathode assembly 19 as shown in FIG. 7 is coated with a brazing material 20 on the outer peripheral surface thereof which does not contribute to electron emission. This is intended to prevent oxygen gas and barium released from the impregnated cathode structure 16. The impregnated cathode assembly used in the Ar ion gas laser tube is brazed because it emits electrons from the entire inner and outer surfaces of the cathode, unlike the cathode that takes out electrons only from the inner surface of the cathode shown in FIG. Since the surface area of the cathode that contributes to plasma discharge is reduced, the life is shortened. The hollow-structured cathode shown in FIG. 7 has the same structure as that of the hollow-structured cathode because the purpose is to take out electrons only from the inner surface of the cathode, but the purpose is completely different. Further, the inner and outer surfaces thereof are smooth surfaces without irregularities, and the heater is exposed outside the hollow cylinder.

[0010]

As described above, the impregnated cathode structure used in the conventional Ar ion laser tube is a direct heat type cathode in which the cathode structure is processed into a spiral coil shape, and a current is directly passed through to heat. Due to the structure, there were the following various problems. 1) Since tungsten, which is a cathode base metal and is a very hard and difficult-to-cut material, is processed into a helical coil shape, it is susceptible to processing vibration, is very difficult to machine, and breaks during processing due to crystalline metal. There is a problem that it is easily broken. 2) Due to the helical structure, it is very fragile and susceptible to vibrations in post-processing operations such as welding, impregnation, and assembly, so that it must be handled carefully. 3) Since the impregnated cathode assembly is constantly heated to about 1100 ° C. during the operation of the Ar ion laser, a temperature gradient is generated at the center and both ends of the spiral cathode assembly during operation, and the impregnated cathode assembly is deformed. Then, there is a problem that short-circuit and disconnection occur, and the plasma discharge stops. 4) In order to prevent a short circuit due to deformation of the spiral shape, it is necessary to set the winding pitch to 1 mm or more. As a result, the dimensions of the cathode and the electron emission area become larger than necessary, and a large current cannot be obtained. Therefore, the current density of the impregnated cathode must be increased. There is a problem that the increase of the current density causes a decrease in reliability such as a short life and a large deformation rate due to the increase of the impregnation type negative temperature.

Accordingly, the present invention has been made in view of the above-mentioned problems of the prior art, and in an impregnated cathode assembly used for a discharge tube such as an Ar ion laser tube, deformation and short circuit of the cathode due to heating are prevented, and the surface area is increased. The purpose of the present invention is to extend the life of the impregnated cathode assembly and increase its reliability by reducing the current density and the operating temperature.

[0012]

In order to achieve the above-mentioned object, an impregnated cathode assembly according to the present invention comprises an inner and outer peripheral surface of a hollow cylindrical porous refractory metal material for securing a laser beam path. Are formed in a concavo-convex shape, a cylindrical heater is buried in the inside of the base to heat the base, and the holes of the base are impregnated with an electron-emitting substance containing barium.

In the impregnated cathode structure, the inner diameter of the base is preferably 1 mm or more so that the laser beam can pass without loss, and the heater is embedded in the base with an insulating material. The heater is held and insulated, and the heater is made of a refractory metal material containing tungsten or molybdenum, or a conductive material containing carbon, and the porous refractory metal material is tungsten alone or molybdenum. , A rhenium, iridium, osmium, ruthenium, scandium, and yttrium.

[0014]

In the impregnated-type cathode assembly of the present invention constructed as described above, the cathode substrate is replaced by a conventional spirally-heated direct heating type cathode, and an inner and outer peripheral surface has an uneven shape and a heater is embedded inside. By using the hollow cylindrical cathode as described above, vibration resistance is improved, machining is facilitated, and a function of preventing cracking and breaking of the cathode substrate in the work of the subsequent process is provided.

Further, by forming the cathode into a hollow cylindrical shape having irregularities on the inner and outer peripheral surfaces, deformation and short circuit of the cathode structure due to heating during operation are prevented, and the cathode can be easily changed only by changing the mechanical dimensions of the irregularities. It is possible to increase the surface area.

Further, not only the problem of the conventional impregnated cathode structure but also the prevention of deformation and short-circuit, the electron emission portion also exists in a portion corresponding to the interval between the winding pitches of the conventional spiral cathode structure. Due to this, the increase in the surface area has the effect of significantly reducing the operating temperature and greatly improving the reliability such as long life.

[0017]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a sectional view showing the structure of an embodiment of an impregnated cathode structure according to the present invention, FIG. 2 is a sectional view of a base which is a main part of the cathode structure shown in FIG. 1, and FIG. 6 is a flowchart for explaining a manufacturing process of the impregnated cathode structure shown in FIG.

The impregnated cathode structure 5 shown in FIG. 1 has a hollow cylindrical body shown in FIG. 2 in which inner and outer peripheral surfaces of a hollow refractory body shown in FIG. The cathode base 1 has a shape, and a spiral heater 2 is embedded in the inside of the cathode base 1 with an insulator 4.

The impregnated cathode assembly 5 is manufactured by the following steps.

As shown in FIG. 3, first, the average particle diameter is 5 μm.
Porous tungsten having a porosity of 20% is manufactured by pressing and molding the tungsten powder of (1) (step S1). The pores of the porous tungsten are impregnated with acrylic resin or copper (Step S2).

Next, porous tungsten impregnated with acrylic resin or copper was formed on a lathe with irregularities on the inner and outer peripheral surfaces as shown in FIG. 2 and an inner diameter of 8 mm and an outer diameter of 12 mm having a space for embedding a heater inside. The cathode substrate 1 is machined (step S3). At this time, the acrylic resin or copper plays a role of a cutting auxiliary oil for cutting tungsten, which is a difficult-to-cut material. Further, when processing with a lathe, the chucking of the lathe is performed reliably because the cathode structure is not a helical shape as in the prior art, and it is possible to prevent breakage and cracking of porous tungsten due to rotational vibration during cutting.

After machining, the cathode substrate 1 is heat-treated to remove unnecessary acrylic resin or copper (step S4).

Then, the heater 2 serving as a heating source is buried in the inside of the cathode base 1 using alumina 3 as an insulator (step S5). Further, 4BaO, CaO, Al ₂ O ₃
Is heated and melted in a hydrogen atmosphere to impregnate the pores of the cathode substrate 1, and a large amount of excess impregnating material adheres to the surface of the cathode structure 1 after the impregnation. The impregnating material is scratched mechanically by tweezers or the like (step S7).

The impregnated cathode assembly manufactured as described above is
Since the inner and outer peripheral surfaces are formed of a hollow cylindrical substrate having irregularities, FIG.
Compared to the conventional spiral-shaped impregnated cathode structure shown in
It is resistant to vibrations during processing, and is unlikely to cause defects such as breakage. Similarly, in an assembling operation in a post-process, it is resistant to vibration and easy to handle.

Further, since the electron-emitting portion is present up to the portion corresponding to the interval between the winding pitches, the surface area of the cathode assembly can be approximately doubled even with the same volume and the same axial length. Even if the same current is obtained by the effect of increasing the surface area, the current density can be halved.
The life can be doubled. And since it does not adopt a helical shape, it is deformed during operation heating, and there is an advantage that defects such as short circuit and disconnection do not occur.

Further, the inner diameter of the hollow portion of the cathode assembly is limited by the beam diameter of the laser beam passing through the hollow, and it is necessary to be 1 mm or more in view of the assembly accuracy of the laser tube.

Since the heater embedded in the cathode structure needs to heat the cathode structure to 1000 ° C. or higher, the same effect can be obtained by using a high melting point material such as molybdenum or carbon other than tungsten, which is conductive. Needless to say, the porous high-melting metal material is not limited to tungsten alone as well as molybdenum,
It goes without saying that a similar effect can be obtained even with a tungsten alloy containing at least one of rhenium, iridium, ruthenium, scandium and yttrium.

[0029]

As described above, according to the present invention, the hollow cylindrical impregnated cathode structure having the inner and outer peripheral surfaces having the uneven shape and having the heater embedded therein is provided. It has the effects of preventing cracking and breaking of the substrate, and preventing deformation and short circuit defects due to heating during operation.

Further, since the surface area can be easily increased only by changing the unevenness size of the inner and outer peripheral surfaces, there is an effect that the current density can be reduced, the operating temperature can be reduced, and the reliability can be improved due to the long life. .

[Brief description of drawings]

FIG. 1 is a sectional view showing the configuration of an embodiment of an impregnated cathode structure according to the present invention.

FIG. 2 is a sectional view of a base which is a main part of the cathode structure shown in FIG.

FIG. 3 is a flowchart for explaining a manufacturing process of the impregnated cathode structure shown in FIG.

FIG. 4 is a diagram showing a schematic configuration of an Ar ion laser tube having an example of a conventional cathode structure.

FIG. 5 is a view showing the structure of a conventional impregnated cathode structure.

FIG. 6 is a schematic sectional view of the configuration of an electron beam generator disclosed in Japanese Patent Application Laid-Open No. 1-187747.

FIG. 7 is a schematic cross-sectional view of a hollow cathode disclosed in JP-A-2-162633.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cathode base 2 Heater 3 Insulator (alumina) 4 Oxide (impregnated material) 5 Impregnated cathode structure

Claims (5)

[Claims] An inner and outer peripheral surface of a hollow cylindrical porous high melting point metal material for securing a laser beam path is formed in an irregular shape, and a cylindrical shape is provided inside the substrate for heating the substrate. An impregnated cathode assembly having a structure in which a heater is embedded and holes of the base are impregnated with an electron-emitting substance containing barium. 2. The impregnated-type cathode assembly according to claim 1, wherein an inner diameter of the substrate is 1 mm or more so that a laser beam can pass therethrough without loss. 3. The impregnated cathode assembly according to claim 1, wherein the heater is embedded, held, and insulated inside the base by an insulating material. 4. The impregnated-type cathode assembly according to claim 1, wherein the heater is made of a refractory metal material containing tungsten or molybdenum, or a conductive material containing carbon. 5. The method according to claim 1, wherein the porous high melting point metal material is composed of tungsten alone or a tungsten alloy containing at least one of molybdenum, rhenium, iridium, osmium, ruthenium, scandium and yttrium. The impregnated cathode structure according to claim 1.