Investigation of plasma and radial ion flow parameters in the vicinity of the spt exit plane

Аuthors

Kim V. P.^*, Merkur'ev D. V.^*, Sidorenko E. K.^*

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: riame4@sokol.ru

Abstract

Results of the plasma potential, temperature of electrons, radial ion flow density and ion energy experimental study in the vicinity of the stationary plasma thruster (SPT) model exit plane are represented in this paper. This SPT model with external accelerating channel diameter of 85mm was developed at RIAME MAI and operated with discharge voltages of (300-800)V and mass flow rates through the mentioned channel of 2.1mg/s and 2.5 mg/s of Xenon. Plasma parameters were measured by several flat electrostatic probes positioned in the vicinity of the thruster exit plane along different radial directions and at the same distance fr om the thruster axes corresponding to the typical distance of cathode position from the mentioned axes. Energy of ions in the vicinity of thruster exit plane was measured by the retarding potential analyzer (RPA). It is shown that character of the plasma parameter dependence on the discharge voltage changed significantly with the increase of the mass flow rate through the thruster accelerating channel from 2.1 mg/s to 2.5 mg/s and that the mean energy of ions was around (80-120) eV and weakly dependant on the discharge voltage within the range of the discharge voltages of (300-800) V. Thus, energy of ions in radial ion flows moving in the vicinity of the thruster exit plane is sufficient to sputter structural elements such as cathode.
There were considered the possible mechanisms of ion generation with relatively high energy discovered in the radial ion flows and it is shown that elastic scattering of the accelerated ions on neutrals can not provide the measured level of the ion current density. Estimations show also that the acceleration of ions appeared near the exit of the accelerating channel by the potential drop in plasma volume due to the electron pressure gradient can not result in the measured energy of ions. Therefore it is concluded that the main source of such ions could be an exit part of the accelerating layer positioned outside the accelerating channel of the studied SPT model wh ere the lines with constant potential near the boundary of the main flow can have configuration causing an acceleration in radial directions of ions appeared near the mentioned boundary.

Keywords:

stationary plasma thrusters, operation modes, vicinity of the thruster exit plane, radial ion flows, plasma parameters, energy of ions

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