RU155777U1 - CONTROLLED DISCHARGE - Google Patents

Abstract

The utility model relates to the field of pulsed technology, to the formation of pulses of currents and voltages, namely to controlled arrester for switching high currents, for use as switches of capacitive energy storage. The technical result of the utility model is to reduce the laser radiation power for switching a spark gap. The technical result is achieved in that in a controlled arrester containing a pulsed laser, a focusing lens and a housing in which a cathode made of VNB-3 alloy and having a tip in the center is located, an anode made with a hole in the center and a transparent window for inputting the beam laser, a nonlinear crystal is installed between the laser and the collecting lens to convert part of the radiation of the first harmonic of the laser into radiation of the second harmonic, and the focusing lens is made of optical glass LK3 or LK6.

Description

Technical field

The utility model relates to the field of pulse technology, to the formation of pulses of currents and voltages, namely, to controlled arrester for switching high currents, for use as switches of capacitive energy storage.

State of the art

Known controlled arrester (Patent of the Russian Federation No. 2302053, H01J 7/64, 2006), containing opposing anode and cathode installed in a sealed insulation housing, piezoelectric sensors are installed inside the chamber, in which one of the electrodes is made wedge-shaped. The electrode has a large area, and its wedge-shaped does not give a high electron yield.

A known laser-controlled spark gap (Patent of the Russian Federation No. 1641161, H01T 1/20, 1994), comprising a housing in which two opposing electrodes are installed, one of the electrodes has a through hole in which a transparent window is installed on the path of the laser beam for input laser beam. The window is covered with a metallized film to create an avalanche flow.

The disadvantage of this arrester is the presence of an avalanche stream spraying electrodes and the walls of the arrester housing, which leads to abnormal breakdowns.

Known dischargers - two-electrode, rarely three-electrode, made in a glass or cermet. They usually use active cathodes: oxidized or thoriated tungsten, nickel coated with potassium or barium, alloys of tungsten, nickel and boron oxide or molybdenum and tungsten. The VNB-3 alloy is produced in the form of a tungsten rod with the composition: W - 92%; Ni - 4.5%; the remainder is boron oxide. СУО 021 048-722 ТУ, 1972. The cathode of VNB-3 alloy has low atomization and low work function. Pure metals are also used: tungsten, stainless steel, molybdenum, aluminum (Shustov MA, Protasevich ET Theory and practice of gas-discharge photography. Tomsk: TPU publishing house. 2001, p. 102-103). The disadvantage of this arrester having a flat cathode is its low efficiency.

Also known controlled arrester (Patent of the Russian Federation for utility model No. 119935, H01J 17/64, publ. 08/27/2012), comprising a housing in which are located: a window for inputting laser radiation; anode with a hole in the center for transmitting laser radiation; a cathode made of VNB-3 alloy containing tungsten 92%, nickel 4.5% and boron oxide 3.5%, and having a tip in the center, as well as a laser and a collecting lens for focusing laser radiation on the tip of the cathode. The specified utility model is selected as a prototype. As a rule, such schemes use a pulsed solid-state laser with a wavelength of 1.06 μm, operating in the modulated Q factor mode (Anisimov V.I., Davydov S.G., Dolgov A.N., Kozlovskaya T.I., Revazov V .O., Seleznev V.P., Yakubov R.Kh. The process of switching a vacuum spark gap with laser control // Uspekhi Applied Physics, 2014, v. 2, No. 6. P. 613-622). The disadvantage of the prototype is the relatively high laser radiation power for the process of switching a spark gap due to the high reflection coefficient of laser radiation by the cathode material at a laser wavelength.

The proposed utility model eliminates this drawback.

The technical result of the utility model is to reduce the laser radiation power for switching a spark gap.

Disclosure of a utility model.

The technical result is achieved in that in a controlled arrester containing a pulsed laser, a focusing lens and a housing in which a cathode made of VNB-3 alloy and having a tip in the center is located, an anode made with a hole in the center and a transparent window for inputting the beam laser. A useful model is distinguished by the fact that a nonlinear crystal is installed between the pulsed laser and the collecting lens to convert part of the radiation of the first harmonic of the pulsed laser to radiation of the second harmonic, and the focusing lens is made of optical glass LKZ or LK6.

A brief description of the drawings.

The essence of the utility model is illustrated in the drawing, which schematically shows a spark gap with laser control, where: 1 - housing of the spark gap; 2 - anode; 3 - cathode; 4 - a window for inputting laser radiation; 5 - pulsed laser; 6 - focusing lens, 7 - nonlinear crystal.

Implementation of a utility model.

The controlled arrester contains a pulsed laser 5, a focusing lens 6 and a housing of the arrester 1, in which there is a cathode 3 made of VNB-3 alloy and having a tip, an anode 2 made with a hole in the center, and a transparent window 4 for inputting the laser beam, between a non-linear crystal 7 is installed by a pulsed laser 5 and a focusing lens 6 to convert part of the radiation of the first harmonic of the laser into radiation of the second harmonic, the focusing lens is made of optical glass LKZ or LK6. As a nonlinear crystal, KDP, DKDP, LiIO ₃ , LiNbO ₃ , etc. crystals can be used.

For the formation of the breakdown process in the spark gap, it is necessary that the laser radiation power density absorbed by the cathode exceeds a certain threshold value necessary for the emission of electrons from the cathode surface, the evaporation of the cathode material, or the formation of plasma at its surface. When exposed to a powerful laser pulse, all three of these phenomena can be observed. If the effect is carried out at the wavelength of the first harmonic of the laser, then the absorbed power density of the laser radiation is determined by the equation

where q _p1 is the power density of the laser radiation absorbed by the cathode when exposed to the first harmonic wavelength;

q ₁ is the power density of the laser radiation [W / m];

R ₁ is the reflection coefficient of the cathode material at a wavelength of the first harmonic of the laser;

R _1l is the reflection coefficient from both surfaces of the lens 6 at the wavelength of the first harmonic of the laser;

R _1w is the reflection coefficient from both surfaces of the window 4 at the wavelength of the first harmonic of the laser;

S _1l is the area of the laser beam [m];

S _1p is the area of the laser beam of the first harmonic at the cathode [m ² ].

It is known that the reflection coefficient of metals nonlinearly depends on the wavelength of the incident radiation and decreases sharply for wavelengths shorter than 1 μm (V.V. Lebedeva. Experimental optics. - 3rd ed. - M .: Publishing House of Moscow State University, 1994. - 352 pp. Libenson MN, Yakovlev EB, Shandybina GD Interaction of laser radiation with matter - Part I. Absorption of laser radiation in matter, edited by V.P. Veiko, St. Petersburg: St. Petersburg State University ITMO, 2008 .-- 142 s).

A nonlinear crystal 7 installed in the optical circuit of the arrester between the pulsed laser 5 and the focusing lens 6 converts part of the radiation of the first harmonic of the laser λ ₁ into radiation of the second harmonic λ ₂ . The effect of laser radiation on the cathode is carried out simultaneously at two wavelengths λ ₁ and λ ₂ . In this case, the laser radiation power density absorbed by the cathode will be

where q _p2 is the power density of the laser radiation absorbed by the cathode when exposed to wavelengths λ _{1 of the} first and λ _{2 of the} second harmonic;

k is the conversion coefficient of the radiation of the first harmonic of the laser into the second;

R _1k is the reflection coefficient from both surfaces of the nonlinear crystal 7 at the wavelength of the first harmonic of the laser;

R ₂ is the reflection coefficient of the cathode material at a wavelength of the second harmonic of the laser;

R _2l is the reflection coefficient from both surfaces of the lens 6 at the wavelength of the second harmonic of the laser;

R _2w is the reflection coefficient from both surfaces of the window 4 at the wavelength of the second harmonic of the laser;

R _2k is the reflection coefficient from one surface of the nonlinear crystal 7 at a wavelength of the second harmonic of the laser;

S _2l is the area of the laser beam of the second harmonic;

S _2p is the area of the second-harmonic laser beam at the cathode.

The first term in equation (2) shows the contribution to the absorbed power at the laser cathode of the non-transformed first harmonic of the laser, and the second term is the contribution of the second harmonic of the laser.

To reduce reflection losses, it is advisable to use materials with the lowest possible reflection coefficients for manufacturing the input window 4 and the focusing lens 6. In addition, to ensure the approximate equality of the areas of the laser beams of the first and second harmonics at the cathode, it is necessary to use a material with a minimum refractive index dispersion coefficient to produce a collecting lens 6. Optical glasses LK3 and LK6 meet these requirements, in which the refractive indices for the wavelength of 1.06 μm are 1.4785 and 1.4614, respectively, and for the wavelength of 0.53 μm they are 1.4900 and 1.473, respectively (GOST 13659-78 Colorless optical glass. Physico-chemical characteristics. Main parameters), that is, they differ by less than 0.8%. Therefore, in equation (2) we can put

Assumptions (3) are due to the fact that the coefficient of reflection of radiation from an optical surface is determined by the relation (V.V. Lebedeva. Experimental optics. - 3rd ed. - M: Publishing house of Moscow State University, 1994. - 352 p.)

where n is the refractive index of the material at the corresponding wavelength, and the focal length of the collecting lens 6 and, therefore, the area of the laser beam at the cathode also depends on the refractive index of the lens material at the corresponding wavelengths. Therefore, at the minimum values of the differences in the values of the refractive indices, they can be neglected. Dividing (2) by (1) and performing the transformations, we obtain:

. Проведем оценки технического результата для катодов, выполненных из вольфрама, никеля и меди. В качестве нелинейного кристалла возьмем иодат лития LiIO₃, у которого показатель преломления для λ₁=1,06 мкм составляет 1,86, для λ₂=0,53 мкм составляет 1,901, а коэффициент k=0,4 (Качмарек Ф. Введение в физику лазеров. М.: Мир, 1980. - 540 с).The technical result is achieved when

. We will evaluate the technical result for cathodes made of tungsten, nickel and copper. As a nonlinear crystal we take lithium iodate LiIO ₃ , for which the refractive index for λ ₁ = 1.06 μm is 1.86, for λ ₂ = 0.53 μm it is 1.901, and the coefficient k = 0.4 (Kachmarek F. Introduction Laser Physics), Moscow: Mir, 1980 .-- 540 s).

Initial data taken from the literature (V.V. Lebedeva. Experimental optics. - 3rd ed. - Moscow: Publishing House of Moscow State University, 1994. - 352 pp .; Libenson MN, Yakovlev EB, Shandybina GD Interaction of laser radiation with matter, Part I. Absorption of laser radiation in matter, edited by V.P. Veiko, St. Petersburg: St. Petersburg State University ITMO, 2008. - 142 pp. And F. Kachmarek Introduction to Laser Physics. M .: Mir, 1980. - 540 p.) And the calculation results are presented in table 1.

The table shows that the absorbed power density of the laser radiation at cathodes from W is 2.4 times higher than the initial one, for a cathode from Ni - 1.16 times, from Cu - 2.75 times. This allows you to reduce the radiation power of a pulsed laser required for switching a spark gap. Since the VNB-3 alloy contains 92% tungsten, the reflection coefficients shown in table 1 for tungsten will be close to the reflection coefficients of the VNB-3 alloy.

The arrester operates as follows.

Before the start of the spark gap operation, a pulsed laser 5 is turned on. The tip of the cathode 3 made of VNB-3 alloy is the focus point of the laser beam. The beam of the pulsed laser 5 is directed to a nonlinear crystal 7, which converts part of the radiation of the first harmonic of the laser into the second harmonic. Focusing lens 6, the radiation of the first and second harmonics of the pulsed laser 5 through the input window 4 is focused on the tip of the cathode 3, where the breakdown processes are formed. The tip of the cathode 3 increases the field strength, reduces the work function of the electrons from the material in the emission zone, leads to an increase in the density of thermoelectrons, which ensure the formation of breakdown processes in the main interelectrode gap of the spark gap. After the formation of the conducting plasma channel between the anode 2 and the cathode 3, energy is transferred from the capacitive storage to the load.

The effect of the radiation of the first and second harmonics of the laser on the cathode leads to an increase in the laser radiation power density absorbed by the cathode, which reduces the laser radiation power for switching the spark gap.

Thus, the proposed technical solution differs from the prototype in the presence of new features and their mutual arrangement, which give the object new properties that are manifested in the technical result.

Claims (1)

A controlled arrester containing a pulsed laser, a focusing lens and a housing in which a cathode made of VNB-3 alloy and having a tip in the center is located, an anode made with a hole in the center, and a transparent window for inputting a laser beam, characterized in that between a nonlinear crystal is mounted with a laser and a focusing lens, and the focusing lens is made of optical glass LK3 or LK6.

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