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

Neutral Particle Flux (NPF) Probe

A small vessel with an ionization pressure gauge that open to ambient plasma conditions through a series of grids that repel all ions and all electrons thereby allowing for a measurement of the neutral particle pressure.

Figure 1. Schematic of a neutral particle flux probe used at PEPL.

The neutral particle flux probe (NPF) is used to examine the neutral particles within plasma. These particles are not affected by electric or magnetic fields and thus are difficult to detect by conventional probe techniques. The only detectable properties of neutral particles are momentum and energy. The momentum of the neutral particles can be estimated by using a highly sensitive vacuum pressure gauge coupled with a charged particle filter. The NPF is essentially a hybrid between an off-the-shelf hot cathode ionization gauge and an RPA. The RPA is set to repel both ions and electrons, allowing only neutral particles to enter the gauge. The flux of these neutral particles will appear as a rise in pressure on the ionization gauge pressure sensor. At equilibrium, the flux of particles out of the gauge must be equal to the flux of particles into the gauge. By using free molecular theory, the flux of particles leaving the tube can be analytically analyzed, allowing for a direct relationship between measured pressure and neutral particle flux.


Selected Relevant Publications

  1. King, L. B., Gallimore, A. D., and Marrese, C. M., "Transport Property Measurements in the Plume of an SPT-100 Hall Thruster," Journal of Propulsion and Power, Vol. 14, No. 3, May-June 1998, 327- 335.
  2. King, L. B., "Transport-property and Mass Spectral Measurements in the Plasma Exhaust Plume of a Hall-effect Space Propulsion System," Ph.D. Dissertation, University of Michigan, 1998.
  3. Marrese, C. M., "Compatibility of Field Emission Cathode and Electric Propulsion Technologies," Ph.D. Dissertation, University of Michigan, 1999.
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