RU2092949C1 - Cathode board for fast-flow gas laser - Google Patents

Abstract

FIELD: laser equipment. SUBSTANCE: device has separate cathodes which have extended emitters which go outside of cathode housing. When potential difference between adjacent cathode is generated due to heterogeneity of gas in main discharge gap, probability of break down along gas between emitters is greater than along longer distance between housings of cathodes. This results in ignition of discharge between extensions of emitters. This discharge by-passes this potential difference and prevents space between electrodes against breakdown. EFFECT: increased reliability. 8 cl, 4 dwg

Description

 The invention relates to quantum electronics and can be used to create electric-discharge lasers with transverse pumping of gas.

 A device for a discharge chamber for a gas laser is known, in which the cathode board is assembled from a set of individual cathodes with independent cooling by water and power supply [1] The disadvantage of this board is the large number of vacuum-water connections, leading to low laser tightness, lower efficiency and reliability.

 A discharge chamber device is also known in which this drawback is absent [2] In this chamber, the cathode board consists of a set of rows consisting of several cathodes each, and the cathodes of one row have a common cooler isolated from them. In this design, the number of vacuum-water compounds is sharply reduced.

 However, this solution has a significant drawback. When a potential difference appears between adjacent cathodes in a row, which occurs when the main discharge is cotraged, that is, when an arc is ignited between one of the cathodes and the anode, a discharge occurs between these cathodes, as a rule, on the insulating surface of the cooler, as a result of which the insulation breaks as between cathodes, and between the cathodes and the cooler, and the cathode row fails.

 To prevent breakdown between the cathodes on the insulated surface of the cooler, the gap between them is filled with an insulating compound. However, the insulating compound is not reliable enough for long-term operation, because due to the appearance of microcracks or delamination of the insulation due to shrinkage of the compound or resulting from aging of the material, there is a possibility of breakdown between the cathodes. In addition, such a chamber is difficult to manufacture and requires the use of organic compounds in the vacuum cavity of the laser, which is undesirable due to significant gas evolution from the volume of the compound, which can lead to a decrease in the energy resource parameters of the gas laser.

 The invention solves the problem of increasing the durability and reliability of the discharge chamber, simplifying its manufacture.

 This is achieved by the fact that the occurrence of overvoltages between the cathodes by a breakdown between them is not prevented, but rather, an early breakdown is possible in a safe zone. For this, the cathodes are made with elongated emitters protruding beyond the cathode body. In this case, in the case of the appearance of a potential difference between adjacent cathodes, arising due to the inhomogeneity of the gas medium in the main discharge gap, and when this potential difference reaches a value greater than the breakdown voltage between the protrusions of the emitters, but less than the breakdown voltage between the cathodes, between the protrusions of the emitters a discharge is ignited, which shunts this potential difference and, thus, protects the gap between the electrodes from breakdown, and therefore, the insulating material from destruction. UV radiation emanating from this discharge is shielded from the heat sink surface by a dielectric gasket, and in this case no gluing of this gasket to the cooler is required.

The dimensions of the protruding part of the emitter and the gap between the emitters should be selected from the condition L> l ≥ d _min ,
Where
L is the distance between the cathodes;
l distance between the ends of the emitters;
d _{min is the} distance between the two electrodes at which the minimum breakdown voltage is realized at the working gas pressure and the given material of the emitters.

Для упрощения изготовления катодного узла целесообразно выполнять катодный узел составным. При этом эмиттер можно изготавливать из эрозионностойкого и дугостойкого материала, например из молибдена или вольфрама, а корпус катода из материала с высокой теплопроводностью, например из алюминиевого сплава. В случае, когда катод делается из алюминиевого сплава, его можно также анодировать для уменьшения вероятности пробоя между катодами.The breakdown voltage between the two electrodes also depends on the pressure and composition of the gas mixture and on the material of the electrodes and is described by the Paschen curve (Yu. P. Raizer. Gas discharge physics. M. Nauka, 1987, p. 323). For each gas-material pair, for a certain value of the product of pressure and the distance between the electrodes (p • d) _min , the minimum value of the breakdown voltage U _{t min} is reached such that the discharge does not light up at a lower voltage. When the value of the product of pressure by the distance between the electrodes is smaller or larger than (p • d) _min , the breakdown voltage increases. Thus, for each given pressure, it is possible to determine the value of d _min at which U _{t min} is realized. So, for example, for copper electrodes and air: at (p • d) _min 1 torr • cm, then at p 20 torr

To simplify the manufacture of the cathode assembly, it is advisable to make the cathode assembly composite. In this case, the emitter can be made of an erosion-resistant and arc-resistant material, for example, of molybdenum or tungsten, and the cathode body of a material with high thermal conductivity, for example, of an aluminum alloy. In the case where the cathode is made of an aluminum alloy, it can also be anodized to reduce the likelihood of breakdown between the cathodes.

 To increase the likelihood of breakdown between the emitters, the protruding tips of the emitters can be made of material with a lower breakdown voltage, which is the same with a higher secondary emission coefficient in some way, for example, by plasma spraying, to apply coatings of such material to the ends of the emitter. A high secondary emission factor lowers the breakdown voltage between emitters. Materials with a high secondary emission coefficient are platinum, silver, etc.

To increase the stability of the discharge and prevent contact of the discharge with the dielectric (facing ceramic), the emitter can be made multilayer, for example, of three layers. Moreover, the materials of these layers to choose from the conditions U _b > U ₀ ,
Where
U _{0 is the} cathodic potential drop for the central layer, for example, for nickel U ₀ 226 V for air (Reiser Yu.P. Gas discharge physics. - M. Nauka, 1987, p. 369);
U _b cathodic potential drop for the lateral layer, for example, for copper U _b 370 V for air (ibid.).

 In this case, the discharge will burn on the central layer of the emitter, and the lateral layers will limit the discharge at the cathode and increase the heat removal from the central layer. It is also possible that the central layer of the emitter has no protrusions, which simplifies its manufacture.

 In FIG. 1 shows a layout of cathode elements; in FIG. 2 - cathode elements, a longitudinal section; in FIG. 3 cathode element, cross section; in FIG. 4 cathode element in the case of a cathode row with a tube cooler, cross section.

 The cathode board is assembled from cathode elements 1, each of which consists of an emitter 2, placed between two parts of the cathode body 3. The cathode body is mounted on a heat sink surface 4 covered with a dielectric layer. The outer walls of the cathode body are lined with a high-temperature dielectric layer 5. Between the surface of the heat sink 4 and the protrusions of the emitter 7, which can be made of material with a lower breakdown voltage, there is a gasket made of a lightproof dielectric 8.

 A variant is possible when the cathode row has a cooler in the form of a tube 10, which is covered by parts of the cathode casing 3. This option is simple and has less laborious manufacturing. The design work is to create a uniform and stable discharge in the active zone of an electric discharge laser. Using this design can improve the durability and reliability of the discharge chamber.

Claims (8)

1. The cathode board of a fast-flowing gas laser, consisting of several rows, each of which is assembled from several cathodes isolated from each other, including a housing with external walls lined with a discharge-resistant dielectric and protruding into the flow emitter, independently connected to a power source and having a common, insulated electrically a cooler from them, characterized in that the emitters are made longer than the cathode body, and the distance between the ends of the emitters of adjacent cathodes is selected from the ratio I am
L> l ≥ d _min ,
where L is the distance between the cathodes;
l distance between the ends of the emitters;
d _{min is the} distance between two emitters,
at which the minimum breakdown voltage is realized at the working gas pressure and the given material of the emitters.  2. The circuit board according to claim 1, characterized in that the cooler is a tube that covers parts of the cathode body.  3. The board according to claim 1 or 2, characterized in that between the ends of the emitters and the dielectric coating of the cooler is placed a lightproof shield made of dielectric.  4. Fee for claims. 1 to 3, characterized in that the cathode is made integral, moreover, the cathode body is made of a material with high thermal conductivity, and the emitter is made of an alloy with high arc resistance and erosion resistance.  5. Fee for claims. 1 to 4, characterized in that the protruding ends of the emitters are coated with a material with a high coefficient of secondary emission.  6. Fee for claims. 1 to 5, characterized in that the emitter is made multilayer, for example of three layers, and the side layers are made of material with a greater cathodic potential drop than the central layer.  7. The board according to claim 6, characterized in that the central layer of the emitter is made without protruding ends.  8. The board according to claim 4, characterized in that the cathode body is made of aluminum alloy with subsequent anodizing.

Images