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Neutral Particle Flux (NPF) Probe: Examines
neutral particles
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.
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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.
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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.
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Marrese,
C. M., "Compatibility of Field Emission Cathode and Electric Propulsion
Technologies," Ph.D.
Dissertation, University of Michigan, 1999.
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