Study of plasma dynamics in the HET relying on global thruster characteristics parameterized with discharge voltage

Abstract

A prototype of krypton Hall-effect thruster (HET) of 0.5 kW nominal power and a dedicated diagnostic system for ion current collection were designed in the laboratory of plasma space propulsion (PlaNS) of the Institute of Plasma Physics and Laser Microfusion (IPPLM) in Warsaw. The diagnostic system consisting of a collimated Faraday Cup (FC) and a Planar Probe with Guarding Ring, named also Faraday Probe (FP) was intended to capture both temporal and spatial ion current variation, allowing to analyze not only ion current dynamics locally but also to estimate the total ion current value and a plasma jet divergence. Reliable engine operation provided by stability of plasma in a discharge channel of the thruster is unambiguously reflected in the oscillations of the discharge current. The so-called breathing mode, categorized as ionization instability with frequencies in the range of 10–30 kHz, is commonly recognized in the HET’s discharge current. Rising of instabilities makes it difficult to increase the specific impulse effectively by just simply attempting to operate thruster in high-voltage regime because it may result in very irregular thruster functioning and often to ceasing of plasma. Discharge current oscillations should also be strongly reflected in the ion current. Indeed, a similar to discharge current behavior was observed in the recorded FC and FP ion current signals. By changing thruster operating conditions, like discharge voltage and magnitude of B-field, transitions between smooth and oscillating current regimes were examined. Studying the ion current dynamics seems particularly important, since it is predicted that the control of discharge instabilities may be crucial to improve the performance of HETs in the future.

Searching for Chaotic Behavior in the Ion Current Waveforms of a Hall Effect Thruster

“…Keeping the main operating parameters unchanged, i.e. a krypton mass flow rate of 0.8 mg/s and a coils current ratio of I inn / I out = 7.0 A / 4.0 A (leading to a magnetic field of up to * 500 G in the thruster channel), the discharge voltage was varied in the range 300-700 V. Other coils current ratios are not considered in this paper and have been reported in other works [25,26]. A comparison of thruster performance with krypton and xenon can be found in [27,28].…”