High-Speed Thruster and Cathode Plasmadynamics

Plasma density during a breathing cycle, measured with a high-speed Langmuir probe with transfer function data fusion techniques.

project personnel
Zachariah Brown, Parker Roberts

principal investigator
Benjamin Jorns

previous personnel
Ethan Dale, Marcel Georgin, Kimberly Trent, Michael Sekerak, Robert Lobbia, Tom Liu, Mike McDonald, Roland Florenz

project sponsors

associated thrusters

Arising from the myriad of electromagnetic interactions between excited propellant particles, electrons, and the imposed magnetic and electric fields, HET plasmas (as well as cathodes, ion thrusters, pulsed plasma discharges, etc.) are rich with oscillation in a wide band ranging from 1 kHz to 20 GHz.

The existence of plasma oscillations in the near- and far-field discharge of a Hall effect thruster alters the conventionally held view of their operation as steady electrostatic propulsion devices. Indeed, the consequences from fluctuations in ionized propellant density, temperature, and potential may include increased thrust, exacerbated engine erosion, and spacecraft interference. In this research project, the unsteady nature of a Hall effect thruster discharge has been investigated via two-dimensional, time-resolved plasma measurements. A novel dual Langmuir probe diagnostic (HDLP, see ref. 2) was developed to enable an unprecedented temporal resolution for electrostatically acquired plasma properties near the upper theoretical limits (1-10 MHz, see ref. 3). Observations of large amplitude transient oscillations caused by the Hall thruster breathing mode were seen for all thruster conditions at all spatial locations and in all measured plasma properties including: discharge current, electron density, electron temperature, plasma potential, and visible light emission. A unique method of spatiotemporal data fusion (see ref. 4) facilitates visualization of two-dimensional time-resolved planar plasma density contour maps of discrete turbulent bursts of plasma ejected as the thruster exhales breaths of ionized propellant at velocities in excess of 12 km/s (see fig. 1). An initial time-resolved investigation of the plasma downstream from a Hall thruster unveiled an environment rich in oscillatory behavior dominated by the Hall thruster breathing mode. These insights emphasize the importance of time-resolved plasma measurements and, through enhanced understanding of the discharge process, may ultimately lead to improved thruster designs that work in concert with plasma fluctuations to achieve enhanced performance. (From ref. 1)

The initial 100-kHz HDLP diagnostic developed for this research provided measurements of unprecedented spatial and temporal detail within a HET plume. However, an examination of the temporal limitations of the probe (from ref. 3) suggests that an upper probing rate of 1-10 MHz is possible. Future development of this capability is already underway, and the finer temporal detail (coupled with a faster 1-Mfps high-speed camera) will enable the examination of higher-frequency plasma oscillations such as the azimuthal modes (ionization, transit-time, drift instability, etc.) common in the very-near-field of HETs. To that end, future measurements using this advanced HDLP to perform internal time-resolved measurements would be tremendously insightful, and are thus part of ongoing research. The strong magnetic fields in this region are known to exhibit anomalous electron transport, and with detailed time-resolved measurements, one could examine the nature of turbulent transport. Additionally, the use of a HDLP for obtaining time-resolved electron energy distribution functions was shown to be promising in early work and there is ongoing effort to obtain time-resolved EEDFs at a rate of 1 MHz. Measurements of the unsteady state of electron equilibrium could help identify transient plasma phenomena that could be tailored to enhance the efficiency of ionization and particle acceleration in Hall thrusters and other plasma devices.

Selected Publications

  • A Time-resolved Investigation of the Hall Thruster Breathing Mode

    Lobbia, R. B

    University of Michigan, Ph.D. Dissertation, 2010

  • Electron Transport in Hall Thrusters

    McDonald, M.

    University of Michigan, Ph.D. Dissertation, 2012

  • Plasma Oscillations and Operational Modes in Hall Effect Thrusters

    Sekerak, M.

    University of Michigan, Ph.D. Dissertation, 2014

  • Time-resolved internal Hall thruster plasma measurements using a high-speed Langmuir probe

    Dale, E.T., Gallimore, A.D., and Lobbia, R.B.

    63rd Joint Army Navy NASA Air Force (JANNAF) Propulsion Meeting/11th MSS/9th LPS/8th SPS Joint Subcommittee Meeting, Phoenix, AZ, December 5-8, 2016

  • Passive High-speed Imaging of Ion Acoustic Turbulence in a Hollow Cathode

    Georgin, M.P., Byrne, M.P., Ciaston, N.E., Jorns, B.A., and Gallimore, A.D

    Atlanta, GA, AIAA-2017-4973, 2017

  • Propagation of ion acoustic wave energy in the plume of a high-current LaB6 hollow cathode

    Jorns, B.A., Dodson, C., Goebel, D.M., and Wirz, R.

    Physical Review E 96, 023208, 23 August 2017

  • Dispersion relation measurements of plasma modes in the near-field plume of a 9-kW magnetically shielded thruster

    Brown, Z. A., and Jorns, B. A.

    35th International Electric Propulsion Conference, Atlanta, GA, IEPC-2017-387, 2017

  • Ion Acoustic Turbulence in the Hollow Cathode Plume of a Hall Effect Thruster

    Cusson, S.E., Brown., Z, Dale, E.T., Jorns, B.A., and Gallimore, A.D.

    54th AIAA/SAE/ASEE Joint Propulsion Conference, Cincinnati, OH, AIAA-2018-4509, July 9-11, 2018

  • Spatial Evolution of Plasma Waves in the Near-field of a Magnetically Shielded Hall Thruster

    Brown, Z. and Jorns, B.A.

    54th AIAA/SAE/ASEE Joint Propulsion Conference, Cincinnati, OH, AIAA-2018-4423, July 9-11, 2018

  • Non-invasive time-resolved measurements of anomalous collision frequency in a Hall thruster

    E.T. Dale and B.A. Jorns

    Physics of Plasmas, Vol. 26, Issue 1, 013516, 2019

  • Experimental Correlation between Anomalous Electron Collision Frequency and Plasma Turbulence in a Hall Effect Thruster

    Brown, Z.A, Dale, E., and Jorns, B.A.

    36th International Electric Propulsion Conference, Vienna, Austria, IEPC-2019-843, 2019

  • Spatial Evolution of Small Wavelength Fluctuations in a Hall Thruster

    Brown, Z.A. and Jorns, B.A.

    Physics of Plasmas, 26, 113504, 2019

  • Non-classical electron transport in the cathode plume of a Hall effect thruster

    Benjamin A. Jorns, Sarah E. Cusson, Zachariah Brown, and Ethan Dale

    Physics of Plasmas, 27, 022311, 18 February 2020

  • Transient non-classical transport in the hollow cathode plume I: measurements of time-varying electron collision frequency

    Georgin, Marcel P; Jorns, Benjamin A. Gallimore, Alec D

    University of Michigan,, 2020

  • Transient non-classical transport in the hollow cathode plume II: evaluation of models for the anomalous collision frequency

    Georgin, Marcel P; Jorns, Benjamin A.

    University of Michigan,, 2020

  • Perspectives on Physics of ExB Discharges Relevant to Plasma Propulsion and Similar Technologies

    Kaganovich, Igor D. et al

    University of Michigan,, 2020

  • Rotational Waves in the Plume of an Externally-Mounted Hall Thruster Cathode

    Shadrach Hepner, Edward Tang, Ethan Dale, and Benjamin A Jorns

    AIAA Journal of Propulsion and Power,, August 5, 2021

  • Experimental measurements of the contribution of plasma turbulence to anomalous collision frequency in a Hall thruster

    Zachariah A. Brown and Benjamin A. Jorns

    AIAA Propulsion and Energy 2021 Forum,, July 2021

  • Experimental characterization of Hall thruster breathing mode dynamics

    Ethan T. Dale, Benjamin A. Jorns

    Journal of Applied Physics,, October 04, 2021

  • Experimental Characterization of Wave-Induced Azimuthal Ion Velocities in a Hollow Cathode Plume

    Parker J. Roberts, Benjamin A. Jorns, and Vernon H. Chaplin

    AIAA SciTech 2022,, January 2022