Modeling of the Plasma Waveguide on the Basis of the Pulse-Periodic High-Pressure Cesium Discharge
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Modeling of the Plasma Waveguide on the Basis of the Pulse-Periodic High-Pressure Cesium Discharge F. G. Bakshta, * and V. F. Lapshina, b, ** a
b Emperor
Ioffe Institute, St. Petersburg, 194021 Russia Alexander I St. Petersburg State Transport University, St. Petersburg, 190031 Russia *e-mail: [email protected] **e-mail: [email protected] Received October 11, 2019; revised October 11, 2019; accepted October 11, 2019
Abstract—Modeling of the pulse-periodic high-pressure cesium discharge on the basis of the radiative gas dynamic equations is executed. Calculation results of radial profiles of the plasma temperature, energy losses on radiation, electron densities and radial velocity of motion are given to various instants from the beginning of a current pulse. It is shown that the discharge under study makes it possible to create almost completely ionized plasma in the hot near-axis area. In this area, electron density increases from the axis to the wall of the tube and the radial profile of concentration has a shape close to parabolic. The time of existence of a plasma waveguide is equal to tens of microseconds, its radius is about a millimeter and the electron density on its axis is about 1017–1018 cm–3. Also, mechanisms of a plasma waveguide formation in the discharge are discussed in the paper. Keywords: low-temperature plasma, gas discharge, cesium, radiative gas dynamics, plasma waveguide DOI: 10.1134/S1063780X20080024
INTRODUCTION A high-pressure pulse-periodic discharge (PPD) in alkali metal vapors has been studied for a long time, first of all, as a source of visible and infrared radiation [1–4]. In this connection, the PPD combustion modes optimal from the point of view of using this discharge as a radiator have been considered previously. The results of the theoretical and experimental studies of such PPD modes in cesium were presented in [5–7]. In this work, we study a high-pressure PPD in cesium in order to show the possibility of designing a plasma waveguide on its basis. Plasma waveguides are designed for channeling the high-power laser radiation and are plasma channels, in which the electron density near the axis increases with radius. At the present time, plasma waveguides based on capillary discharges have been studied well enough and they are widely used [8, 9]. The specificity of the waveguide on the basis of PPD in cesium is the substantially longer duration of its existence, the lower plasma temperature, the larger channel radius and the relative ease of the implementation. STATEMENT OF WORK The discharge under study is implemented in a sapphire tube (Al2O3) with an internal radius of R ~ 2–
3 mm and a length of 8–10 cm. In this work, the steady-state combustion is considered, when a current pulse of a given shape I(t) and the amplitude Imax of up to 500 A and highly is passed periodically with a frequency of ν ~ 200–1000 Hz through a weakly ionized plasma that either cools after a previous current pulse or is specially supported by a standby discharge with the current I0 ~
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