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(EX/C4-6) Core Fluctuations and Current Profile Dynamics in the MST Reversed-Field Pinch

D.L. Brower1), W.X. Ding1), J. Lei2), J.K. Anderson3), T.M. Biewer3), B.E. Chapman3), K.A. Connor2), D. Craig3), D.R. Demers2), C.B. Forest3), D. Holly3), R. O’Connell3), S.C. Prager3), J.S. Sarff3), P.M. Schoch2), S.D. Terry1), J.C. Wright3)
 
1) Electrical Engineering Department, University of California at Los Angeles, Los Angeles, CA, USA
2) Electrical, Computer and Systems Engineering Department, Rensselaer Polytechnic Institute, Troy, New York, USA
3) Physics Department, University of Wisconsin-Madison, Madison, Wisconsin, USA

Abstract.  First measurement of the current density profile, magnetic fluctuations and e.s particle flux in the core of a high-temperature rfp are presented. We report three new results: (1) The current density peaks during the slow ramp phase of the sawtooth cycle and flattens promptly at the crash. Profile flattening can be linked to magnetic relaxation and the dynamo which is predicted to drive anti-parallel current in the core. Measured core magnetic fluctuations are observed to increases three-fold at the crash. Between sawtooth crashes, measurements indicate the particle flux driven by e.s. fluctuations is too small to account for the total radial particle flux. (2) Core magnetic fluctuations are observed to decrease at least two-fold in plasmas where energy confinement time improves ten-fold. In this case, the radial particle flux is also reduced, being consistent with core e.s. fluctuation-induced transport. (3) The parallel current density increases in the outer region of the plasma during high confinement, as expected, due to the applied edge parallel electric field. However, the core current density also increases due to dynamo reduction and the emergence of runaway electrons.

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IAEA 2003