Numerical modeling of a pulsed plasma thruster

Summary form only given, as follows. Numerical simulations of a pulsed plasma thruster (PPT) were conducted to provide insight into the plasmadynamics and to provide the initial conditions required for plume studies. The approach was to validate a numerical model by comparing computed results with experimental data. The MACH2 computer code was chosen for these studies and the ablation rate of the Teflon propellant was obtained from an optically thin radiation model developed at UTSI. The data used for model validation was the Burton and Bushman (1999) experiments made with a "capillary" configuration where a hollow cylinder of Teflon was clamped between a brass anode and a conical boron nitride nozzle. The mass loss and impulse bit were reported, as well as the capacitor energy and energy efficiency, electron number density, electron temperature, and Mach number in the exhaust plume. These experimental values were used to select radiation parameters used in the ablation model. A typical example of the numeric simulation five microseconds into the discharge gives a maximum calculated temperature of 10 eV in the capillary that decreases both axially and radially to about 2 eV at the nozzle exit. The maximum density occurs at the capillary wall in the relatively cool ablated Teflon products. There is a strong radial density gradient in the capillary corresponding to the temperature gradient, but throughout the nozzle expansion the gradient is primarily axial. The current pulse is essentially complete in ten microseconds, and during this time electromagnetic forces accelerate a small amount of plasma. However, most of the impulse is produced by expansion of the residual high-pressure plasma during the next 50 to 100 microseconds. The simulations indicate that approximately 90 per cent of the total impulse is thermal, which agrees well with the value reported by Burton.