Active control of resistive wall modes in RFPs
Author: Per R. Brunsell
Submitted: 2006-02-04 09:38:13
Co-authors: T.Bolzonella, D.Yadikin, D.Gregoratto, R.Paccagnella, M.Cecconello, J.R.Drake, M.Kuldkepp, G.Manduchi, G.Marchiori, S.Menmuir, S.Ortolani, RFX Team
Royal Inst of Technology
Stockholm, Stockholm 10044
Active magnetic feedback suppression of resistive wall modes (RWMs) is of common interest for several fusion concepts relying on close conducting walls for stabilization of ideal MHD modes. In the advanced tokamak without plasma rotation, the kink mode is not completely stabilized, but rather converted to a RWM with a growth time comparable to the wall time. The instability may limit the attainable beta. For ITER advanced scenario, the attainable normalised beta would increase from 2.5 to 3.5 with RWM feedback control. In the RFP a range of modes is unstable. Hence, the requirement for simultaneous feedback stabilization of multiple independent RWMs arises for the RFP configuration. Recent experiments on RWM feedback stabilization on the EXTRAP T2R and RFX thin shell RFP devices have been highly successful. The experimental results obtained are the first demonstration of simultaneous feedback control of multiple independent RWMs. Using an array of active magnetic coils, a reproducible suppression of all unstable RWMs is achieved for the duration of the discharge, equivalent to about 10 wall times on EXTRAP T2R, through feedback action. An array with 128 saddle coils at 4 poloidal and 32 toroidal positions is used on T2R. Preliminary feedback control on RFX have yielded a significantly improved plasma performance at high plasma currents up to 800 kA.