Electromagnetic Effects in the Near Field Plume Exhaust of a Micro-Pulsed-Plasma Thruster

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A model is presented of the near-field plasma-plume of a pulsed plasma thruster (PPT). As a working example, a micro-PPT developed at the U.S. Air Force Research Laboratory is considered. This is a miniaturized design of the axisymmetric PPT with a thrust in the 10-µ N range that utilizes TeflonTM as a propellant. The plasma plume is simulated using a hybrid fluid‐particle-in-cell direct simulation Monte Carlo approach. The plasma plume model is combined with Teflon 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. Teflon ablation and plasma generation analyses show that the Teflon surface temperature and plasma parameters are strongly nonuniform in the radial direction. The plasma density near the propellant surface peaks at about 10 24 m −3 , whereas the electron temperature peaks at about 4 eV near the electrodes. The plume simulation shows that a region with high density is developed at a few millimeters from the thruster exit plane at the axis. This high-density region exists during the entire pulse, but the plasma density decreases from about 2 × × 10 22 m −3 at the beginning of the pulse down to 0.3 × × 10 22 m −3 at 5 µs. The velocity phase is centered at about 20 km/s in the axial direction. At later stages of the pulse, there are two ion populations with positive and negative radial velocity. Electron and neutral densities predicted by the plume model are compared with near-field measurements using a two-color interferometer, and good agreement is obtained.