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Discharge Chamber Performance of the NEXIS Ion ThrusterThe Nuclear-Electric Xenon Ion System (NEXIS) thruster was designed to produce greater than or equal to 70% efficiency at ISPs in excess of 6500 sec and total power levels in excess of 15 kW. In order to achieve this performance, the thruster requires a large area plasma generator capable of high propellant utilimtion efficiency and low discharge loss while producing a very flat, uniform beam profile. Fortunately, larger thrusters can be made more uniform and efficient due to the higher volume to surface ratio, provided that the magnetic cusp confinement is designed properly and the thruster length to diameter ratio is adequate. This paper describes the discharge chamber performance of the NEXIS Laboratory Model (LM) thruster. The LM discharge chamber is 65 cm in diameter at the grid plane and uses 6 ring-cusps to provide magnetic confinement of the plasma. The thruster was tested with flat carbon-carbon composite grids with the hole pattern masked to 57 cm in diameter and a conventional Type-B "1/2" diameter hollow cathode. During the preliminary "discharge only" tests, the LM thruster demonstrated profile factors of 0.84 and a discharge loss of about 160 eV/ion at 25 V discharge voltage and over 90% propellant utilization efficiency in simulated beam extraction experiments at 3.9 A of beam current. Analysis of the data from these tests used the discharge-only model developed by Brophy. Subsequent beam extraction experiments validated the key variables used in the model to predict the performance from the discharge-only data, and demonstrated 3.9 A of beam current at over 90% propellant utilization efficiency with a flatness parameter of better than 0.8 and a discharge loss of about 185 eV/ion. The slightly higher discharge loss measured during beam extractions was found to be due to a lower screen transparency in the as-manufactured LM grid set. Plasma measurements with a scanning probe internal to the thruster near the screen grid showed plasma densities over l x 10(exp 11) per cubic centimeter and electron temperatures of 3.5 to 5.5 eV depending on the operation parameters. The performance of the NEXIS discharge chamber contributed to the over 78% thruster efficiency measured during beam extraction at 7500 sec ISP and 25 kW of power, and over 81% thruster efficiency measured at 8500 sec ISP.
Document ID
20070023372
Acquisition Source
Jet Propulsion Laboratory
Document Type
Conference Paper
External Source(s)
Authors
Goebel, Dan M.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Polk, James
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Sengupta, Anita
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
FROM
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Date Acquired
August 23, 2013
Publication Date
July 12, 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 Society of Mechanical Engineers, American Inst. of Aeronautics and Astronautics, Society of Automotive Engineers, Inc.
Distribution Limits
Public
Copyright
Other
Keywords
plasma generation
ion propulsion

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