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1

Theoretical analysis of the influence of the power supply on breathing oscillations in Hall thrusters

Barral S.

Journal of Technical Physics

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2008

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Vol. 49, no 3-4

177-185

EN

The breathing mode is the best known low-frequency longitudinal bulk instability of Hall thrusters, capable of generating very wide, regular discharge current oscillations in the 10-30 kHz range. This study extends a recent theory of breathing mode oscillations to the case of a non-ideal voltage source. A simple equivalent circuit modeling the AC behavior of the thruster is derived, using R, L and C components. The equivalent circuit explains in a straightforward way why an impedance in series with the generator is usually able to damp oscillations. More generally, the derived equivalent circuit can be expected to greatly improve the understanding of interactions between the thruster and the power processing unit, and in turn to help the design of robust filters.

2

Current and plasma oscillation characterization in a PPS®-X000 Hall-effect thruster

Kurzyna J., Makowski K., Peradzyński Z., Lazurenko A., Mazouffre S., Coduti G., Dudeck M.

Journal of Technical Physics

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2008

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Vol. 49, no 3-4

267-282

EN

The correlations between local plasma oscillations and the discharge current or cathode potential variations are studied in a high-voltage Hall-effect thruster (HET). A set of electric probes is used to collect the signals. The probes are located in the exhaust region of the thruster, beyond its outer circumference. Measurements are performed for various probe positions and bias potentials, within a wide range of thruster operating conditions. The non-stationary signals are subsequently expanded into finite sets of intrinsic modes with the use of the Empirical Mode Decomposition (EMD) method. The Hilbert-Huang power spectra indicate characteristic bands in the low frequency (LF, tens of kHz), medium frequency (MF) and high frequency (HF, tens of MHz) range. However, the regular HF emission that has been observed in our previous low-voltage characterization of a PPS-100 thruster, is only observable in some particular operating conditions. When the supply voltage is low (e.g. 400 V), the known electrostatic drift wave propagating along the thruster azimuth is unambiguously identified in the probe signals. For higher voltages, HF spectra are usually broadband and do not highlight well the defined peaks. HF emission becomes very irregular or even seemingly random. On the other hand, when regular waves appear (intermittently or in series of bursts), frequencies in the ss 5-100 MHz band can be observed. The oscillations within the MF band that were previously weak in the PPS-100 thruster, appear now to dominate the discharge current spectrum when the thruster operates at the highest voltages. Intense oscillations in the MF range are identified with the use of positively biased probes and by examination of the cathode potential and discharge current variations. The correlations of all the mentioned signals are clear in this frequency band. Correlating the oscillations in the HF band with the MF discharge current wave, one can deduce that HF oscillations are periodically triggered by MF waves at high voltage, while at lower voltage they are triggered by the LF breathing mode, as previously observed in the case of the PPS-100 thruster.

3

On the charging of a dust particle immersed in a plasma: theory and experiment

Allen J. E.

Journal of Technical Physics

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2002

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Vol. 43, no 3

241-255

EN

A review is given of the theory of charging of a dust particle according to the Orbital Motion Limited (OML) theory. This is followed by a summary of a more complete orbital theory that includes the concept of an absorption radius, or effective potential barrier, for the positive ions. Measurements of the charge acquired by a dust particle are then described, using the method of damped dust oscillations employed at Oxford.