Data-driven analysis of breathing mode and ion-transit mode in 2D hybrid Hall thruster simulations

A data-driven modal analysis of low frequency oscillations in a SPT-100-like Hall thruster in the 1--100 kHz range is presented. The used data were generated with a two-dimensional (axial-radial) particle-in-cell (PIC)/fluid simulation code. While proper orthogonal decomposition is unable to uncouple the different dynamics successfully, (higher order) dynamic mode decomposition (HODMD) cleanly isolates the breathing and ion-transit-time modes. Additionally, it facilitates separating transients from the attractors in the data. Thus, the resulting HODMD components can be clustered into two distinct groups with multiple harmonics, enabling the reconstruction of the dynamics of the breathing and ion-transit modes. We show that each plasma variable exhibits a different behavior in each cluster (global oscillations or traveling-wave oscillations), and their amplitudes and frequencies depend on the thruster operating point. This work illustrates the potential of the applied techniques to dissect more complex physics of Hall thrusters and other devices.