|icc_2007_poster.pdf||2007-03-29 11:26:15||David Ennis|
Current and Momentum Relaxation in the MST Reversed Field Pinch
Author: David A Ennis
Requested Type: Poster Only
Submitted: 2006-12-18 18:02:08
Co-authors: A.F. Almagri, D.L. Brower, D. Craig, B.H. Deng, D.J. Den Hartog, W.X. Ding, G. Fiksel, S. Gangadhara, A. Kuritsyn, M. Miller, S.C. Prager, J.S. Sarff, T. Yates
University of Wisconsin-Madison
1150 Universtiy Ave
Madison, WI 53706
Current and momentum relaxation can be important processes in many innovative confinement devices, including the reversed field pinch, spheromak, and the field reversed configuration. In the Madison Symmetric Torus (MST) we observe sudden relaxation of both the current and momentum profile during large current-driven reconnection events (sawtooth crashes). Redistribution of the current profile occurs through correlated products of magnetic field fluctuations with both velocity fluctuations (MHD dynamo < v × b >) and current fluctuations (Hall dynamo < j × b >). Dynamo action is also present between sawtooth crashes. Recently, profiles of poloidal ion velocity fluctuations associated with tearing modes were measured between reconnection events using Charge Exchange Recombination Spectroscopy. Strong correlations are observed for a range of magnetic modes with poloidal mode number m = 1, and the relative phase implies a contribution to the total MHD dynamo away from the magnetic axis. The Hall dynamo mechanism, measured with laser Faraday rotation in the core and probes in the edge, is observed to be large during reconnection events but spatially localized to tearing mode resonant surfaces. Momentum transport in MST also results from the product of the fluctuating current and magnetic field (Maxwell stress < j × b >). It appears that Maxwell stresses in the core and edge of the plasma are larger than the rate of momentum change during reconnection events, suggesting the Reynolds’ stress (< ρ(v⋅∇)v >) might be significant.
Work supported by U.S.D.O.E. and N.S.F.