Simulation of Direct‐Current Microdischarges for Application in Electro‐Thermal Class of Small Satellite Propulsion Devices

Abstract

Microdischarges are miniature non-equilibrium plasma discharges with characteristic dimensions of ∼10's-100's µm and relatively high operating pressures of ∼10's-100's Torr. Microdischarges possess several unique properties that have been exploited in a number of new applications. We have recently proposed a microdischargebased electro-thermal class of microthrusters for small satellite propulsion. These devices utilize intense gas heating in microdischarges to preheat a propellant gas stream before it is expanded in a micronozzle to produce thrust; thereby improving specific impulse of the device over a conventional cold gas microthruster. This paper addresses direct-current microdischarge phenomena in a flowing gas stream. A two-dimensional, selfconsistent, fluid model of a helium microdischarge in a bulk gas flow is developed. For relatively high current/power levels considered in this study, the microdischarge operates in an abnormal glow mode with positive differential resistivity. Increasing discharge pressures for fixed power and bulk flow rates results in a decrease in charged species densities and the electron and gas temperatures. Also the discharge becomes increasingly constricted with increasing pressures, resulting in a more normal glow mode-like operation. Increasing bulk flow rates results in exactly the same trends as increasing pressures. For given input power and pressure, there exists an optimum flow rate for which the average outlet gas temperature from the discharge is a maximum. An increase in input electrical power results in an almost linear increase in the gas temperatures; this property of microdischarges is the key feature that is exploited in our microdischarge-based thruster concept.

Simulation of Direct-Current Surface Plasma Discharge Phenomena in High-Speed Flow Actuation

“…The discharge model used in this paper is based on a 2-D selfconsistent multispecies multitemperature continuum description of the plasma [24], [25]. The individual species number densities (n k ) in the discharge are determined by the species continuity equation…”

“…The convection-diffusion terms in the above governing equations are discretized in space using a hybridpower law scheme that is equivalent to the Scharfetter-Gummel exponential scheme [38]. Temporal discretization is performed using a fully implicit approach, and the nonlinear system of governing equations is solved using the Newton's approach [24], [25].…”

Microplasma thruster powered by X-band microwaves

“…The electromagnetic thrusters rely on the plasma acceleration via interaction of the current and magnetic fields: micro pulsed plasma thrusters. 31,32 The electrothermal thrusters rely on the plasma/gas heating via plasma discharge followed by supersonic plasma/ gas expansion through de Laval nozzles: micro arcjet thrusters, 33,34 hollow cathode thrusters, 35 and plasma thrusters using dc microdischarges, 36,37 ac/rf microcavity discharges, 38,39 capacitively coupled rf discharges in a dielectric tube, [40][41][42][43][44][45][46][47] and microwave discharges. 48,49 We have developed a mm-scale microplasma thruster of the electrothermal type with azimuthally symmetric surface wave-excited plasmas (SWPs), [50][51][52][53][54][55][56][57][58] consisting of a microplasma source followed by a converging-diverging micronozzle as schematically shown in Fig.…”

Modeling of Mode Transition Behavior in Argon Microhollow Cathode Discharges

“…Microdischarges have gained considerable interest in the plasma community over the past decade 1–6. As the name suggests, these discharges are generated in small geometries with characteristic dimensions of tens to hundreds of micrometers.…”

“…These properties of microdischarges open up possibilities for new applications. Indeed, novel uses of microdischarges have been proposed in photonics,2 environmental applications,3 chemical analysis,4 and micropropulsion 5, 6. Basic understanding of these discharges is still limited in part because of their small size, which makes the application of conventional plasma diagnostics difficult.…”