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Experimental Characterization of High Frequency Instabilities within the Discharge Channel of a Hall Thruster

Knoll, AK and Cappelli, M (2009) Experimental Characterization of High Frequency Instabilities within the Discharge Channel of a Hall Thruster In: 31st International Electric Propulsion Conference, 2009-09-20 - 2009-09-24, Ann Arbor, Michigan.

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This study examines the detailed dispersion properties of high frequency (1- 15 MHz) plasma fluctuations within a Hall thruster. The results reveal the existence of two strong modes in this frequency range, which are predominantly axially propagating, with weaker azimuthal waves near the exit and near field region. Both modes show generally similar dispersion characteristics. Each propagates predominantly towards the anode within the discharge, and towards the cathode in the near field. Each is characterized by low wavenumber cut-offs (near 4.5 MHz and 10.5 MHz respectively). In all cases, within the channel, the results seem to be only weakly dependent on axial position, indicating that these disturbances are highly non-local. The wavenumber lies within a range of 100-700 rad/m, and the phase velocities fall in the range of 105 5x105 m/s. The azimuthal components near the exit of the discharge have phase velocities approaching the azimuthal electron drift velocity, but their dispersive characteristics fall short of what is expected for a typical beam plasma mode. We suspect that the because the frequency of these waves lie close to the lower-hybrid resonance, that these waves are the result of an interaction between the lower hybrid waves and the electron stream mode, driven and coupled by the relatively strong transverse electron shear flow, the scale length of which corresponds closely to the measured wavelengths.

Item Type: Conference or Workshop Item (UNSPECIFIED)
Divisions : Surrey research (other units)
Authors : Knoll, AK and Cappelli, M
Date : 20 September 2009
Depositing User : Symplectic Elements
Date Deposited : 28 Mar 2017 13:21
Last Modified : 23 Jan 2020 13:01

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