Hybrid simulation of weakly-ionized rarefied arc-jet flowing supersonically along diverging magnetic field

Summary form only given. We report numerical simulation of supersonic helium plasma jet with neutral kinetics. Since the Knudsen number of the ion flow is larger than 0.01, the plasma flow has to be treated as a particle model. It is found that the ionization degree of the plasma is about 0.01 at most. Consequently, we should solve the kinetics of neutral particles simultaneously by a particle model. However, since the Debye length is about several mm, PIC scheme requires too fine discretization. As a result, we chose hybrid simulation, i.e., Direct Simulation Monte Carlo (DSMC) method for neutral particles and ions, and fluid method for electrons. Residual molecules in the vacuum chamber are also included as particles.We calculate number density, velocity, temperature and electric potential of charged particles and neutrals when the arc plasma flows out of the uniform magnetic field into lower pressure region in a steady state. As a result, we find the velocity increase just after passing the open magnetic field line, followed by deceleration due to collisions with residual molecules1. We also find the temperature increase during the deceleration. In these acceleration-deceleration phenomena, the velocity difference between neutrals and charged species are found, which also changes the electric potential. We discuss the mechanisms of potential formation along the plasma flow mainly by the pressure difference and the friction force between the charged particles and neutral species. The numerical results are, at least qualitatively, consistent with our previous experimental results2.