Computational simulation of coupled nonequilibrium discharge and compressible flow phenomena in a microplasma thruster

Abstract

The microplasma thruster (MPT) concept is a simple extension of a cold gas micronozzle propulsion device, where a direct-current microdischarge is used to preheat the gas stream to improve the specific impulse of the device. Here we study a prototypical MPT device using a detailed, self-consistently coupled plasma and flow computational model. The model describes the microdischarge power deposition, plasma dynamics, gas-phase chemical kinetics, coupling of the plasma phenomena with high-speed flow, and overall propulsion system performance. Compared to a cold gas micronozzle, a significant increase in specific impulse is obtained from the power deposition in the diverging section of the MPT nozzle. For a discharge voltage of 750 V, a power input of 650 mW, and an argon mass flow rate of 5 SCCM (SCCM denotes cubic centimeter per minute at STP), the specific impulse of the device is increased by a factor of ∼1.5 to about 74 s. The microdischarge remains mostly confined inside the micronozzle and operates in an abnormal glow discharge regime. Gas heating, primarily due to ion Joule heating, is found to have a strong influence on the overall discharge behavior. The study provides a validation of the MPT concept as a simple and effective approach to improve the performance of micronozzle cold gas propulsion devices.

Thrust and Efficiency Performance of the Microcavity Discharge Thruster

“…The monomer Ar* metastable is the dominant radical in both the discharges although the relative concentration of the dimer metastable Ar 2 * to the monomer metastable is much higher in the micro DBD case compared to the classic DBD. We note that similar high densities of dimer ion and metastable species are reported in high-pressure DC microdischarges (Deconinck, 2009). …”

“…The electron densities are much lower (~10 ) in the classic DBD case but the sheath thickness is a much smaller fraction of the gas gap distance resulting in a well-defined bulk plasma region. For this case, the electron densities in the bulk plasma remain steady through the cycle at a nearly uniform value of about 6x10 Electron volumetric generation occurs through five different pathways in the highpressure argon chemical reaction mechanism used in this study (Deconinck, 2009). Electron-impact ionization of neutrals (Ar) and metastable argon (Ar*), Penning ionization of Ar*, Penning ionization of Ar 2 * and electron-impact ionization of Ar 2 * are the important pathways.…”

“…The plasma governing equations are solved over an unstructured mesh using a semi-implicit finite volume method. The model also uses finite rate argon chemistry (Deconinck, 2009) which will be described below. The electrons are assumed to have a different temperature compared to the heavy species.…”

“…The detailed chemistry and mobility calculations used in the model are described in (Deconinck, 2009) and (Deconinck, 2008). The ion diffusion coefficients are calculated using the Einstein relation, (4.6) The coefficient of thermal conductivity that appears in the gas energy equation is calculated as .…”

Recent advances in the modeling and computer simulations of non-equilibrium plasma discharges

“…Microdischarges are also the basis for a number of applications including plasma display panels [19], and as lighting sources [20]. Recently, novel application of microdischarges in plasma micropropulsion [21], as logic circuit elements [22], and as lattice elements in large arrays of microdischarges for plasma metamaterials/photonic crystals for the manipulation of electromagnetic waves [23], have been explored. This special issue presents two papers on microdischarges.…”