The University of Michigan
Department of Aerospace Engineering
| Plasmadynamics & Electric Propulsion Laboratory |
Plasma Diagnostics

Top Hat Electric Propulsion Plume Analyzer (TOPAZ)

An electrostatic probe that determines the energy, mass, and angular distributions of ions in the far-field plume.

Figure 1. Bottom view showing base plate detail of the Pro/ENGINEER model of TOPAZ with a quarter cut-away section. (From ref. 1).

One technique for determining the energy-to-charge (E/q) distribution of plasma is to use an electrostatic analyzer. A specific geometry for the electrostatic analyzer, which allows for angular measurements in a wide field-of-view, is the top hat analyzer. This electrostatic analyzer consists of two concentric hemispheres, with an aperture at the apex of the outer hemisphere. Figure 1 illustrates the main components of the top hat analyzer.

Figure 2. The major components and a typical ion trajectory for a top hat electrostatic analyzer.

The inner hemisphere is biased to a negative voltage while the outer hemisphere is grounded. The electric field created between the plates allows for particles within a specific energy range (corresponding to the inner plate voltage) to pass through the aperture and through the gap between the plates. By virtue of its geometry, the top hat analyzer is capable of having a nearly 360-degree azimuthal (horizontal angle) field-of-view.

Figure 3. Final Construction of TOPAZ. (From ref. 1)

Steering electric fields allow for a field-of-view in the vertical direction as well. Through the electrostatics and geometry of the top hat analyzer, the energy-per-charge, azimuthal angle, and elevation angle of incoming ions is measured.

By integrating a mass spectrometer with the top hat analyzer, the velocity distribution of the plasma (within the field-of-view) can be determined. The distribution function allows for derivation of macroscopic properties such as the transport properties and temperature of the plasma through integration over velocity space. Due to the high atomic mass of propellants (i.e., Krypton and Xenon), the charge states within the plume are also easily isolated through use of the mass spectrometer. A time-of-flight method is employed for TOPAZ by utilizing the Top Hat Plate as a gating (timing) gate and the channel as the drift region for the ions.

Figure 4. TOPAZ (covered in a graphite shroud) placed one meter downstream from the BHT-600 Hall Thruster Cluster inside the Large Vacuum Test Facility (LVTF).


Selected Relevant Publications

  1. Victor, A. L., "Design and Utilization of a Top Hat Analyzer for Hall Thruster Plume Diagnostics," Ph.D. Dissertation, University of Michigan, 2006.
  2. Victor. A. L., Zurbuchen, T. H., Gallimore, A. D., "Top hat electrostatic analyzer for far-field electric propulsion plume diagnostics," Review of Scientific Instruments. Vol. 77, No. 1, January 2006.
  3. Victor. A. L., Zurbuchen, T. H., Gallimore, A. D., "Ion-Energy Plume Diagnostics on the BHT-600 Hall Thruster Cluster," Journal of Propulsion and Power, Vol. 22, No. 6, November-December 2006.
  4. Victor, A. L., Zurbuchen, T., Gallimore, A. D., "Development of the Top Hat Electric Propulsion Plume Analyzer (TOPAZ): Mass Analyzer Design and Preliminary Calibration Data," IEPC-2005-016, 29th International Electric Propulsion Conference, Princeton, NJ, Oct 31-Nov 4, 2005.
  5. Victor, A. L., Zurbuchen, T. H., Gallimore, A. D., "The Top Hat Electric Propulsion Plume Analyzer (TOPAZ): Preliminary Data on the BHT-600 Cluster", AIAA-2005-3870, 41st Joint Propulsion Conference, Tucson AZ, July 10-13, 2005.
  6. Victor, A. L., Zurbuchen, T. H., Gallimore, A. D., "Development of the Top Hat Electric Propulsion Plume Analyzer (TOPAZ)," AIAA-2004-4099, 40th Joint Propulsion Conference, Fort Lauderdale, FL, July 11-14, 2004.
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