Modeling of Microdischarges for Use in Microthrusters

Summary form only given. Microdischarges having characteristic dimensions of 100s of mum at pressures of 10s to 100s of torr are being investigated for use as sources of thrust for small satellites. These devices are capable of generating up to mN of thrust using non-contaminating propellants such as rare gases or hydrogen. The class of device of interest includes cylindrical multistage discharges with or without nozzles. The dominant mode of propulsion is by imparting thermal energy to the neutral gas by the discharge. Innovative designs may also take advantage of transfer of momentum from ions to the neutral gas. In this talk, this class of microdischarge will be computationally investigated using a 2-dimensional plasma hydrodynamics model having an unstructured mesh to resolve non-equilibrium electron, ion and neutral transport using fluid equations. Sheath accelerated, beam-like electrons are addressed using a Monte Carlo simulation. A compressible Navier-Stokes module provides the bulk fluid velocities and temperatures. Changes in surface properties are addressed with a surface site-balance model. Results from a parametric investigation of pressure (a few 10s to 100s of torr) and geometry will be discussed for rare gas mixtures with the goal of maximizing the velocity of the exhaust at the exit plane. Velocities of up to 100s m/s have been predicted in the throats of the devices with plasma densities of 10¹³-10¹⁴ cm^-3 at pressures of 50 torr with a back pressure of 30 torr