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Does Sweet-Parker reconnection occur in Field Reversed Configurations?

Author: Tom Intrator
Requested Type: Consider for Invited
Submitted: 2011-06-01 10:40:12

Co-authors: L. Steinhauer, J. Sears, T. Weber

Contact Info:
Los Alamos Natl Lab
TA35, bldg 421
Los Alamos, NM   87545
USA

Abstract Text:
Field Reversed Configurations (FRC's) have toroidal plasma geometry with closed flux surfaces, and a magnetic axis where oppositely directed magnetic fields are in close proximity, and their associated flux annihilates.
The ratio of toroidal electric field $E$ to current density $J$ corresponds to an anomalously large resistivity $eta_{* perp}$ that is much larger than that expected from Coulomb collisions.
There is a resistive like flux dissipation process with anomalously large power density $eta_{* perp} J^2$, which may be driven by tearing instabilities near the separatrix.
If the flux annihilation rate can be interpreted as a magnetic reconnection rate, the standard rigid rotor model predicts it to be inversely proportional to an anomalously collisional Lundquist number $S_{* perp}$ that can be defined in the conventional manner using the radial scale length. On the other hand, if S is defined using using Spitzer resistivity and the standard Sweet-Parker elongated current sheet length, the reconnection rate resembles the Sweet-Parker rate $ approx S_{* perp}^{-1/2}$.
This is surprising, since there is no obvious global change in magnetic topology that is usually taken to be the signature of magnetic reconnection, nor is there ideal current sheet geometry to allow outflow of compressed plasma magnetic flux. We show data from a worldwide database that make this case and discuss recent ideas about formation of islands from unstable reconnection current sheets that are consistent with this conclusion.

Characterization: D1,D6

Comments:

University of Washington

Workshop on Innovation in Fusion Science (ICC2011) and
US-Japan Workshop on Compact Torus Plasma
August 16-19, 2011
Seattle, Washington

ICC 2011