Numerical investigation and modeling of stationary plasma thruster low frequency oscillations

The origin of the oscillations in the range 1-100 kHz, which have been observed during the working of stationary plasma thruster (SPT) is not well understood until now. The purpose of this paper is first to clarify the nature of these oscillations and second to propose an explanation using the concept of current instabilities proposed by Buneman. To reach this objective, a spectral study of the linear instabilities has been performed with a stationary quasineutral hybrid model. These computations show unambiguously a relationship between the nonlinear oscillations that appear in the transient simulation and the growth rate of the linear model. A simplified model is also derived, which highlights the role played by the coupling between the electric field and the ion current leading to Buneman's instabilities. This study suggests to reduce the amplitude of the oscillations controlling the growth rate of the linear mode by modifying the profile of the magnetic field inside the SPT channel. Numerical simulations illustrate the performances of the improvement