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Experimentally Determined Plasma Parameters in a 30 cm Ion EngineSingle planar Langmuir probes and fiber optic probes are used to concurrently measure the plasma properties and neutral density variation in a 30cm diameter ion engine discharge chamber, from the immediate vicinity of the keeper to the near grid plasma region. The fiber optic probe consists of a collimated optical fiber recessed into a double bore ceramic tube fitted with a stainless steel light-limiting window. The optical fiber probe is used to measure the emission intensity of excited neutral xenon for a small volume of plasma, at various radial and axial locations. The single Langmuir probes, are used to generate current-voltage characteristics at a total of 140 spatial locations inside the discharge chamber. Assuming a maxwellian distribution for the electron population, the Langmuir probe traces provide spatially resolved measurements of plasma potential, electron temperature, and plasma density. Data reduction for the NSTAR TH8 and TH15 throttle points indicates an electron temperature range of 1 to 7.9 eV and an electron density range of 4e10 to le13 cm(sup -3), throughout the discharge chamber, consistent with the results in the literature. Plasma potential estimates, computed from the first derivative of the probe characteristic, indicate potential from 0.5V to 11V above the discharge voltage along the thruster centerline. These values are believed to be excessively high due to the sampling of the primary electron population along the thruster centerline. Relative neutral density profiles are also obtained with a fiber optic probe sampling photon flux from the 823.1 nm excited to ground state transition. Plasma parameter measurements and neutral density profiles will be presented as a function of probe location and engine discharge conditions. A discussion of the measured electron energy distribution function will also be presented, with regards to variation from pure maxwellian. It has been found that there is a distinct primary population found along the thruster centerline, which causes estimates of electron temperature, electron density, and plasma potential, to err on the high side, due this energetic population. Computation of the energy distribution fimction of the plasma clearly indicates the presence of primaries, whose presence become less obvious with radial distance from the main discharge plume.
Document ID
20070023371
Acquisition Source
Jet Propulsion Laboratory
Document Type
Preprint (Draft being sent to journal)
External Source(s)
Authors
Sengupta, Anita
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Goebel, Dan
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Fitzgerald, Dennis
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Owens, Al
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Tynan, George
(California Univ. San Diego, CA, United States)
Dorner, Russ
(California Univ. San Diego, CA, United States)
Date Acquired
August 23, 2013
Publication Date
July 11, 2004
Subject Category
Plasma Physics
Meeting Information
Meeting: 40th AIAA/ASME/SAE/ASEE Joint Propulsion Conference
Location: Fort Lauderdale, FL
Country: United States
Start Date: July 11, 2004
End Date: July 14, 2004
Sponsors: American Society for Electrical Engineers, American Inst. of Aeronautics and Astronautics, Society of Automotive Engineers, Inc., American Society of Mechanical Engineers
Distribution Limits
Public
Copyright
Other
Keywords
near grid plasma
ion engines
optical fiber plasma

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