Electromagnetic Effects in the Near Field Plume Exhaust of a Micro-Pulsed Plasma Thruster
AIR FORCE RESEARCH LAB EDWARDS AFB CA PROPULSION DIRECTORATE WEST
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In this work we present a model of the near field plasma plume of a Pulsed Plasma Thruster PPT. As a working example we consider a micro-PPT developed at the Air Force Research Laboratory. This is a miniaturized design of the axisymmetric PPT with a thrust in the 10 micro-N range that utilizes TeflonTrademarksup Trademark as a propellant. The plasma plume is simulated using a hybrid fluid-PIC-DSMC approach. The plasma plume model is combined with TeflonTrademark ablation and plasma generation models that provide boundary conditions for the plume. This approach provides a consistent description of the plasma flow from the surface into the near plume. The magnetic field diffusion into the plume region is also considered and plasma acceleration by the electromagnetic mechanism is studied. TeflonTrademark ablation and plasma generation analyses show that file TeflonTrademark surface temperature and plasma parameters are strongly non-uniform in the radial direction. The plasma density near the propellant surface peaks at about 10exp 24cu m in the middle of the propellant face while the electron temperature peaks at about 4 eV near the electrodes. The plume simulation shows that a dense plasma focus is developed at a few millimeters from the thruster exit plane at the axis. This plasma focus exists during the entire pulse, but the plasma density in the focus decreases from about 2x10exp 22cu m at the beginning of the pulse down to 0.3x10exp 22cu m at 5 microsec. The velocity phase is centered at about 20 kms in the axial direction. At later stages of the pulse there are two ion populations with positive and negative radial velocity. Electron densities predicted by file plume model are compared with near field measurements using a Herriot Cell technique and very good agreement is obtained.
- Electric and Ion Propulsion