Experimental study of radiofrequency cathode-neutralizer

Аuthors

Smirnov P. E.^*, Khartov S. A.^**, Kashulin A. P.^***

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

*e-mail: paulsmyt93@gmail.com
**e-mail: skhartov@ya.ru
***e-mail: ap-k@list.ru

Abstract

High specific impulse and low mass-flow rate of ion thrusters (IT) make them increasingly popular choice as a spacecraft propulsion system. Recent missions demonstrate the efficiency of these thrusters in such missions as orbit correction and exploration of Solar system. Moreover, there are many developing ideas of creating spacecraft with IT for wider spectrum of missions. However, IT needs to have a longer operation time, due to the small thrust (about several mN).

As a rule, such thrusters failure occurs due to the destruction of Ion Optics electrodes or failure of electron source. IT needs electron sources as a main cathode (for plasma producing), and as a cathode-neutralizer (to neutralize potentials of ion beam). Hollow cathodes are most used devices for Ion propulsion applications, due to low gas consumption and high electron current density.

Application of lanthanum hexaboride or tungsten with BaO impregnating as an emitter material, leads to the necessity of strict sustenance of hollow cathodes operational parameters. Interaction of emitter material with a small quantity of poison gas leads to its surface contamination and, as a consequence, to decreasing of the recoverable current even down to zero. It leads to more requirements to the gas purity, and hollow cathode handling prior to its placement in space. Moreover, to ensure effective operation, the emitter should be heated up to 0.6-0.8 of its melting temperature by the external heater, which, in turn, causes the emitter material evaporation (life span reduction), power consumption increase and longer cathode start-up procedure.

The problems of high reliability of traditional electron sources for ion thrusters led the authors to the idea apply them as cathode with plasma high-frequency discharge. In such device, plasma is generated and sustained by radiofrequency induction discharge. The absence of “loaded” (high temperature, powerful flows of charged particles) electrodes eliminates all problems of the cathode long-term operation provision. As with hollow cathode, the bulk plasma volume acts as an electron emitter, which allows generate high electron currents. The article describes the scheme of the prototype of this device, and the results of its experimental development. Currents generated by the high-frequency cathode were achieving up to 1.7 A at the input power of 120 W. Effectiveness evaluation of the high-frequency cathode is presented.

Keywords:

electron source, radiofrequency discharge, ion thruster cathode, cathode-neutraliser

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