Ion dynamic characterization using phase-resolved laser-induced fluorescence spectroscopy in a Hall effect thruster.

Significant information on the dynamics of the plasma constituents in Hall effect thrusters can be obtained using minimally intrusive techniques, such as laser-induced fluorescence (LIF) diagnostics. Indeed, LIF provides an excellent tool to determine the ion velocity distribution function with high spatial resolution. Even in a steady-state operation, recording time-resolved maps of the velocity distribution is relevant due to persisting time-dependent features of the thruster discharge. One of the preeminent phenomena that render the ion velocity distribution to be time dependent is commonly attributed to the breathing mode, characterized by pronounced oscillations in the discharge current. The goal of this work is to propose a new technique for plasma dynamic studies based on LIF spectroscopy with phase-resolution during the breathing period. For this purpose, the Hilbert transform is used to define the instantaneous phase of oscillation of the thruster current. Ion velocity distribution modification over assigned phases of oscillation is measured simultaneously and in real-time thanks to a fully numerical analysis of the data.

Measurement of XeI and XeII velocity in the near exit plane of a low-power Hall effect thruster by light induced fluorescence spectroscopy.

Near exit plane non-resonant light induced fluorescence spectroscopy is performed in a Hall effect low-power Xenon thruster at discharge voltage of 250 V and anode flow rate of 0.7 mg/s. Measurements of the axial and radial velocity components are performed, exciting the 6s(2)[3/2]2(o)→6p(2)[3/2]2 transition at 823.16 nm in XeI and the 5d[4]7/2→6p[3]5/2(o) transition at 834.724 nm in XeII. No significant deviation from the thermal velocity is observed for XeI. Two most probable ion velocities are registered at a given position with respect to the thruster axis, which are mainly attributed to different areas of creation of ions inside the acceleration channel. The spatial resolution of the set-up is limited by the laser beam size (radius of the order of 0.5 mm) and the fluorescence collection optics, which have a view spot diameter of 8 mm.

Note: An advanced in situ diagnostic system for characterization of electric propulsion thrusters and ion beam sources.

We present an advanced diagnostic system for in situ characterization of electric propulsion thrusters and ion beam sources. The system uses a high-precision five-axis positioning system with a modular setup and the following diagnostic tools: a telemicroscopy head for optical imaging, a triangular laser head for surface profile scanning, a pyrometer for temperature scanning, a Faraday probe for current density mapping, and an energy-selective mass spectrometer for beam characterization (energy and mass distribution, composition). The capabilities of our diagnostic system are demonstrated with a Hall effect thruster SPT-100D EM1.