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SMALL-SCALE ELECTRON DENSITY FLUCTUATIONS IN THE HALL THRUSTER, INVESTIGATED BY COLLECTIVE LIGHT SCATTERING

Abstract : Anomalous electron transport across magnetic field lines in the Hall thruster plasma is believed to be due in part to plasma oscillations. Oscillations of frequencies on the order of a few megahertz and of wavelengths on the order of a millimeter have been shown to be likely to lead to transport. Measurements of fluctuations at these length scales is, however, beyond the reach of conventional thruster diagnostics such as probes. This work describes the first application of a specially-designed collective light scattering diagnostic (PRAXIS) to the measurement of electron density fluctuations and the subsequent identification of unstable modes in the thruster plasma. Two main high frequency modes are identified, propagating azimuthally and axially, of millimetric length scales and megahertz frequencies. The propagation directions and angular openings of the modes are determined. The azimuthallypropagating mode, believed to be responsible for transport, is shown to have wave vector components antiparallel to the magnetic field and parallel to the electric field, and to propagate within an extremely limited region. The axially-propagating mode is shown to have features closely related to the ion beam velocity and divergence. The electron density fluctuation level is calculated and is associated with a high electric field amplitude. The experiments, confirming a number of predictions arising from linear kinetic theory, also provide much additional information permitting the improvement and development of models for both modes.
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https://pastel.archives-ouvertes.fr/tel-00484027
Contributor : Sedina Tsikata <>
Submitted on : Monday, May 17, 2010 - 4:33:49 PM
Last modification on : Friday, October 16, 2020 - 3:21:53 AM
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  • HAL Id : tel-00484027, version 1

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Sedina Tsikata. SMALL-SCALE ELECTRON DENSITY FLUCTUATIONS IN THE HALL THRUSTER, INVESTIGATED BY COLLECTIVE LIGHT SCATTERING. Physics [physics]. Ecole Polytechnique X, 2009. English. ⟨tel-00484027⟩

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