Non-intrusive tools for electric propulsion diagnostics

This paper reports about the advances in non-intrusive diagnostic systems for ion thruster engines undergoing at Aerospazio Tecnologie. Among the various optical diagnostics developed and applied in electric propulsion, laser-induced fluorescence (LIF) is a powerful, non-intrusive and species selective technique. It is capable to bring knowledge, where other techniques cannot be applied, as for example in the ionization region. Thanks to its selectivity to a given species, LIF can provide valuable information also about the neutrals. Another important topic is the occurrence of regular plasma oscillation in Hall thrusters channel, being correlated in different complex ways with performance of the thruster. In particular, it has been demonstrated that rotating inhomogeneity in the plasma ring (also termed rotating spokes) can be one of the principal mechanisms explaining quantitatively the anomalous electron transport in the discharge channel. Since the electron transport affects directly the efficiency in Hall thrusters, the characterization of plasma oscillation results in a valuable tool to assess the conditions for optimal thruster operation. The ultra-fast imaging technique offers the chance for a non-intrusive optical diagnostics of the plasma oscillation with high spatial and temporal resolution. In this paper, we propose a new approach to this technique to obtain higher frequency resolution and higher contrast by optical filtering. Both techniques are successfully applied as diagnostic tools of Aerospazio 200 W Xenon fed Hall effect thruster.