Plasma expansion in a paraxial magnetic nozzle

PLASMA EXPANSION IN A PARAXIAL MAGNETIC NOZZLE Christopher A. Deline and Brian E.Gilchrist University of Michigan Ann Arbor, MI 48109 Greg Chavers Propulsion Research Center, NASA / Marshall Space Flight Center, Huntsville, Alabama 35812 Several space propulsion systems have been proposed that could possibly realize mass efficiency gains over prior systems1,2. These propulsion systems utilize magnetic nozzles with strong magnetic fields to shape a plasma flow into a directed jet. The ability of strongly magnetized plasma to break free from the confining field in these systems is critical for efficient momentum transfer to the plasma exhaust. MHD theory3 and simulation4 each predict that momentum will be transferred once the flow kinetic energy density WK is greater than WB the magnetic field energy density. An experiment is being conducted at NASA Marshall Space Flight Center which tests this theory. Multiple plasma sources and feed gasses are being used including Hydrogen plasma in both a washer gun and helicon source. A paraxial magnetic nozzle guides the plasma with straight diverging field lines to the nozzle aperture. High flow velocities at the nozzle aperture suggest that the flow is super-Alfvénic at this point (WK > WB). Diagnostics used in the experiment to verify the effects of super-Alfvénic detachment include measurements from hall probes, langmuir probes, RF interferometer and flux loops. This poster will present experiment configuration and preliminary results from various diagnostics. 1. F.R. Chang Diaz, “Research Status of the Variable Specific Impulse Magnetoplasma Rocket”, Fusion Technology 35 (1T) 1999 pp. 87-93. 2. J.Gilland, “Application of a Helicon Discharge to Electric Propulsion”, 34th AIAA Joint Propulsion Conference, 1998 paper 3934. 3. A.V. Arefiev, B.N. Breizman, “Magnetohydrodynamic Scenario of Plasma Detachment in a Magnetic Nozzle” Physics of Plasmas 12 (4) 2005. 4. A.V. Ilin, F.R. Chang-Diaz, J.P. Squire, A.G. Tarditi, B.N. Breizman, M.D. Carter, “Simulations of Plasma Detachment in VASIMR” 40th AIAA Aerospace Sciences Meeting, 2002 paper 0346.