ZARM MPD multi-Region Foam

Peng Liang

Before the plasma is fully ionized, deviations form kinetic equilibrium are rather common, especially in the fringes of arcs and close to electrodes. As the mobility of electrons in the plasma is much larger than that of ions and atoms, it's easily understood that the kinetic energy gained from electric field will be transferred during ion-electron and atom-electron collision from electrons into atoms and ions. Furthermore, due to the relatively small mass of electrons, the energy exchange in-between will be rather inefficient, so the temperature of electrons will be much higher than that of atoms and ions especially when the electric field strength is high.

Different from the local thermodynamics equilibrium (LTE) achieved in fully ionized plasma, the non-equilibrium case requires temperatures of both (electron Te and heavy particle Th) for defining the plasma state. Based on the OpenFoam built-in solver ChtMultiRegionFoam, which is designed to handle heat transfer between solids and fluids, we set out to add new transport equations concerning two-temperature models in the plasma region and at the same time taking ionization-recombination equilibrium and ambipolar transport of particles into account, under the assumption that the temperature of atoms and ions are the same and the argon atoms are only singly ionized thus the number density of electrons and ions are also the same. The Poisson equation will be carefully implemented into the sheath layer of both electrodes' vicinity where two-temperature model is no more applicable. The goals of all the implementations are to get a good view of electron production during discharge especially near the electrodes and the overall temperature and electrical potential distribution of our MPD thruster to achieve a better thermal design and management.