Temporal Anti-Aliasing Method for High Speed Imaging of Hall Effect Thrusters

A temporal anti-aliasing technique for detecting plasma oscillations beyond the Nyquist limit of high-speed diagnostics is applied to imaging datasets taken of the Advanced Electric Propulsion System (AEPS) Engineering Test Unit 2 (ETU2) operating at the 600 V, 12.5 kW condition in Vacuum Facility 5 (VF-5). The theoretical underpinnings of the algorithm are presented, and the technique is first demonstrated on synthetic data. Spectral analysis of high-speed imaging data is performed at multiple sampling frequencies. In addition to global and cathode-localized modes, potentially aliased frequencies are identified and cross-checked against camera artifacts, leading to the detection of a 1.46 MHz global mode. This temporal anti-aliasing technique thus demonstrates potential to extend the frequency range of diagnostics beyond their Nyquist limit by combining datasets through a Bayesian inference framework.