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Emission parameters of a hot cathode in a low pressure discharge


I.K. Belova – Ph.D.(Phys.-Math.), Associate professor, Chair “Software, information technologies, and applied mathematics”, Kaluga branch of the Bauman MSTU
E.O. Deriugina – Ph.D.(Eng.), Associate professor, Chair “Computer systems, complexes, and networks”, Kaluga branch of the Bauman MSTU

In the number of science and technology areas high intensity gas - discharge devices that use heavy-current discharge with thermionic (white-hot) cathode (hot cathode) are widely adopted. Among them, the most typical are the ionic gas-discharge lasers, in which voltaic arcis used for their excitation. Hot cathode in these devices should provide high electrons density to create aheavy-current low-pressure arc and low level nebulization with heavy ion bombardment of the surface for a few thousand hours. The usage in gas-discharge ion lasers at ionized thermal cathodes gases designed for other devices classes didn’t allow us to provide durability more than 50…100 hours. So the problem of creating low dispersing cathodes with durability of several thousand hours of reliable and durable devices. Hot cathode is the central node of gas discharge laser, with its parameters the influence of other factors on its main parameters is traced: the physical processes, providing heating, operating temperature reaching time, emission current, durability. When the gas pressure at the surface of the cathode changes, the space charge structure could reallocate, resulting in an increase of the emission current. Studies have proved that the increase in the emission current is more for gases with a greater relative atomic mass. In the moment of reaching the operating cathode temperature are porous metallic sponge coated with the active substance, the active substance filling the pores of the sponge and is a chemical compound interacting with the metal sponge (reductant) allocates free barium, which activates the cathode. In operation process of the aluminate and aluminosilicate cathode active substance react with the matrix tungsten forming core barium tungstate, free barium and other reaction products. Free barium diffuses to the surface and reduces cathode work function. Forming tungstates have high dielectric properties, and concatenating (partially) matrix metal, increase cathode resistivity during its operation. The main inhibiting factor of the hot cathode is the formation of antungstate tungstate and other products of the reaction, obstructing diffusion of aluminum silicate to tungsten matrix. Another factor that slows down this reactions is avarage cathode temperature reduction, due to an increase in its electrical resistance.

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May 29, 2020

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