Evaluation and Active Control of Clustered Hall Thruster Discharge Oscillations

While preliminary experiments with a cluster of four Busek 200-Watt (BHT-200-X3) Closed Drift Hall thrusters indicate reasonable performance scalability from single thruster experiments, cluster plume interactions are believed to give rise to an increased ion energy spectrum as well as cross-talk and synchronization between the thruster discharges. Recent experiments with a higher power cluster of four 600-Watt (BHT-600) Hall thrusters have exhibited similar clustering behavior. Discharge voltage and current characteristics are studied in detail with frequency magnitude and phase analysis from low frequencies up to 100 kHz. Modulation of the electromagnetic circuit current provides data for the analysis of multiple correlations between the various signals, thereby quantifying all interdependencies. Accentuation and shifting of various modal features (including the so called “breathing” mode) are observed in the clustered configuration. We are then motivated to provide active stabilization of the observed oscillations in an effort to improve thruster lifetimes, overall efficiency, and performance. After identification of the thruster cluster system, various models and control algorithms are developed to provide stabilizing feedback control to the clustered Hall thrusters. Application of this control in real time has shown reductions in the discharge oscillations during thruster startup and steady operation.