We present experimental results on the characterization of ID-Hall, a double stage Hall thruster with an inductively coupled magnetized ionization stage. This first experimental prototype of ID-Hall operates in a low power regime, typically below 400 W. The purpose of this work is not only to study the properties of ID-Hall and provide directions for optimization but also, and more generally, to study the relevance of the double stage concept with respect to important physical issues such as current oscillations and anomalous electron transport. We present experimental measurements of the current–voltage characteristics, extracted ion beam current (Faraday cup measurements), and ion energy and angular distribution functions (RPA measurements) in single and double stage regimes of operation, as a function of DC voltage and RF power. The results demonstrate that ions can be extracted from the inductive RF ionization stage even under conditions where the applied DC voltage is not sufficient to ionize the gas flow, i.e., ID-Hall can indeed operate in a double stage regime. At intermediate voltages, the overshoot observed in the current–voltage characteristics of single stage thrusters disappears in double stage operation, indicating a decrease in anomalous electron transport. Time-resolved and time-averaged ion energy distribution measurements show a coupling between ion energy, breathing mode oscillations, and the magnetic configuration of ID-Hall.

Hall thrusters are known to exhibit a large variety of instabilities. Their physical mechanisms have been identified at low (kHz) and intermediate (MHz) frequencies, even though they are still not fully understood. Furthermore, electromagnetic radiations generated by Hall thrusters, named “self-emission” of the thruster, have been measured from kHz to MHz as expected from the identified instabilities, but also at higher frequencies. The origin of the high frequency (GHz) self-emission remains for now unknown. Assessing this self-emission, that is important for understanding the physics of Hall thrusters as well as for electromagnetic compatibility issues with the spacecraft, is challenging. Another aspect that makes the understanding of the physics of Hall thrusters complex comes from the eventual coupling between instabilities, which has been recently suggested and observed. The aim of this paper is to explore the possibility of characterizing simultaneously instabilities in Hall thrusters on a broadband frequency range (from kHz to GHz) in situ, meaning in a conventionally used vacuum chamber where Hall thrusters are usually operated. We show in this paper that, despite the reverberant nature of the vacuum metallic chamber, useful information is extracted at low and intermediate frequencies and even at high frequency from the measurements done with an antenna in this environment.