Propagation and Evolution of the Electron Cyclotron Drift Instability in a Hall Thruster: Fitting Experimental Data and Analytical Models*

Plasma oscillations in the acceleration region and near-field plume of a magnetically shielded Hall thruster are identified as the electron cyclotron drift instability. Using a high speed electrostatic probe diagnostic, spatially resolved dispersion relations are measured. At the acceleration region, distinct cyclotron resonances are observed between 3-20 MHz. In the near-field plume the resonances are still evident, but spectral power becomes dominant around 100-500 kHz, associated with the sharp appearance of a linear ion acoustic like wave. The experimental dispersion is fitted to linear analytical models and agreement between the measured and theoretical dispersion is demonstrated. The growth of the low frequency oscillations is characterized and shown to agree with recent non-linear simulations of the electron cyclotron drift instability.