Comparison of Theory with Rotation Measurements in JET ICRH Plasmas
Authors: R.V. Budny, C.S. Chang, C. Giroud, R.J. Goldston, D. McCune, J. Ongena, F.W. Perkins, R.B. White, K.-D. Zastrow, and contributors to the EFDA-JET Work Programme
Date of PPPL Report: June 2001
Presented at: the 28th EPS Conference on Controlled Fusion and Plasma Physics, Madeira, Portugal, June 18-22, 2001.
Plasma rotation appears to improve plasma performance by increasing the E x B flow shearing rate, thus decreasing radial correlations in the microturbulence. Also plasma rotation can increase the stability to resistive MHD modes. In the Joint European Torus (JET), toroidal rotation rates wtor with high Mach numbers are generally measured in NBI-heated plasmas (since the neutral beams aim in the co-plasma current direction). They are considerably lower with only ICRH (and Ohmic) heating, but still surprisingly large considering that ICRH appears to inject relatively small amounts of angular momentum. Either the applied torques are larger than naively expected, or the anomalous transport of angular momentum is smaller than expected. Since ICRH is one of the main candidates for heating next-step tokamaks, and for creating burning plasmas in future tokamak reactors, this paper attempts to understand ICRH-induced plasma rotation.
The spin-up in the core region during the diagnostic NBI is in quantitative agreement the NBI torques. The steady rotation near the edge is in qualitative agreement with a theory of X-point ion loss. The largest steady rotation, measured near the outer mid-radius, is too large in magnitude and has the wrong sign (positive) for the inboard resonance plasmas to be explained by the theoretically proposed ICRH-induced torques.