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Title: Magnetic reconnection process in transient coaxial helicity injection

The physics of magnetic reconnection and fast flux closure in transient coaxial helicity injection experiments in NSTX is examined using resistive MHD simulations. These simulations have been performed using the NIMROD code with fixed boundary flux (including NSTX poloidal coil currents) in the NSTX experimental geometry. Simulations show that an X point is formed in the injector region, followed by formation of closed flux surfaces within 0.5 ms after the driven injector voltage and injector current begin to rapidly decrease. As the injector voltage is turned off, the field lines tend to untwist in the toroidal direction and magnetic field compression exerts a radial J × B force and generates a bi-directional radial E{sub toroidal}×B{sub poloidal} pinch flow to bring oppositely directed field lines closer together to reconnect. At sufficiently low magnetic diffusivity (high Lundquist number), and with a sufficiently narrow injector flux footprint width, the oppositely directed field lines have sufficient time to reconnect (before dissipating), leading to the formation of closed flux surfaces. The reconnection process is shown to have transient Sweet-Parker characteristics.
Authors:
 [1] ;  [2] ;  [3] ;  [4]
  1. Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey 08544 (United States)
  2. Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
  3. University of Wisconsin, Madison, Wisconsin 53706 (United States)
  4. University of Washington, Seattle, Washington 98195 (United States)
Publication Date:
OSTI Identifier:
22220568
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 20; Journal Issue: 9; Other Information: (c) 2013 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CURRENTS; ELECTRIC POTENTIAL; MAGNETIC FIELDS; MAGNETIC RECONNECTION; MAGNETIC SURFACES; MAGNETOHYDRODYNAMICS; NSTX DEVICE; PINCH EFFECT; PLASMA; PLASMA SIMULATION; TRANSIENTS