Hall2De Simulations with a First-principles Electron Transport Model Based on the Electron Cyclotron Drift Instability

摘要

After several years of effort that combined a wide range of plasma measurements in a 6-kW laboratory Hall thruster and r-z numerical simulations with HalI2De, the spatial variation of the anomalous collision frequency needed in Ohm's law to produce the observed thruster behavior has now been isolated. This numerical solution is used here to test the validity of a first-principles model of the anomalous transport in these devices before such model is implemented self-consistently in r-z fluid codes like HaI12De. The first-principles model employs quasi-linear theory and is based on the hypothesis that the Electron Cyclotron Drift Instability (ECDI) excites ion acoustic turbulence that, in turn, enhances the effective collision frequency in these devices. We find that an idealized model of the ECDI with Maxwellian velocity distributions for electrons and singly-charged, main-beam, cold ions (T_i=0.07 eV) is insufficient to explain the expected variation of the anomalous collision frequency both in the interior and exterior of the acceleration channel. When warm ions (~0.5-3 eV) are accounted for, the ECDI model in the channel interior appears more promising but fails by orders of magnitude in the near plume region due to the much higher Landau damping of the ion acoustic waves there. This implies that either (a) one or more processes allow the ECDI instability to remain uninhibited by classical Landau damping or, (b) that a different instability (or instabilities) altogether, also insusceptible to Landau damping, is/are active in this region. A previous hypothesis, that convection of wave energy generated by the ECDI in the channel plays a significant role in the near plume, is not supported by the results of the simulations.