Stability Analysis of Hall Thrusters

The H6 Hall thruster operating nominally. Although it looks steady by the naked eye, most thrusters oscillate strongly ~10 kHz.

project personnel
Ethan Dale

affiliated personnel
Kentaro Hara (PDML)

previous personnel
Michael Sekerak

project sponsors

associated thrusters

Despite active research on Hall thrusters for the past several decades, the fundamental physics governing their operation is still unclear. One aspect of this is the presence of strong oscillations in these devices that are not fully understood. The most prominent oscillations are the breathing mode and spoke mode. The former is a global instability that is most easily detected as a periodic change in discharge current. The latter is a local azimuthal instability that can be detected with a segmented anode or by optical emission.

Understanding the nature of these instabilities is important because they have been shown to correlate with changes in performance yet they cannot always be faithfully captured by simulation. Without understanding them, theses instabilities could potentially be characterized with extensive ground testing. However, thorough ground testing becomes impractical for high-power thrusters, and thus accurate simulation is crucial. By improving the physical understanding of these oscillations, they can be simulated more accurately.

The nature of these instabilities is explored in several ways. First, their relationship with global thruster parameters like thrust and discharge current are examined to uncover correlation between them. Second, the instabilities can be characterized experimentally to establish dispersion and then compared to theoretical dispersion relations to identify that source of the instability. Third, simple models of the Hall thruster plasma can be employed to predict the frequency and growth rate of these instabilities, using the experimental characterization for validation.

It has been shown for the H6 thruster that thrust-to-power peaks during the transition between the breathing mode and spoke mode. The magnetically-shielded H6MS shows similar behavior. Empirical dispersion relations for the spoke mode have been found but do not obviously match a common type of wave. Stationary zero-dimensional models of the Hall thruster channel have been found insufficient to predict a growing instability from a linear perturbation analysis.

Selected Publications

  • Plasma Oscillations and Operational Modes in Hall Effect Thrusters

    Sekerak, M.

    University of Michigan, Ph.D. Dissertation, 2014

  • Mode Transitions in Hall-Effect Thrusters Induced by Variable Magnetic Field Strength

    M.J. Sekerak, A.D. Gallimore, D.L. Brown, R.R. Hofer, and J.E. Polk

    AIAA Journal of Propulsion and Power, 10.2514/1.B35709, March 2016

  • Perturbation analysis of ionization oscillations in Hall effect thrusters

    K. Hara, M.J. Sekerak, I.D. Boyd, and A.D. Gallimore

    Physics of Plasmas, Vol. 21, Issue. 20, pg. 122103, 2014

  • Mode transition of a Hall thruster discharge plasma

    K. Hara, M.J. Sekerak, I.D. Boyd, and A.D. Gallimore

    Journal of Applied Physics, Vol. 115, Issue 20, pg. 203304, 2014