NTM and error field proposals slide 1 R J Buttery, NSTX forum, Nov 2007 XP810 review Error field sensitivity of 2/1 NTM onset thresholds at high and low rotation (and later extension to counter rotation) R J Buttery 1 with R. J. La Haye 2, S. Sabbagh 3, E. J. Strait 2. 1 EURATOM/UKAEA Fusion Association, Culham Science Centre, UK. 2 General Atomics, USA 3 Columbia University, NY Work conducted under the European Fusion Development Agreement and jointly funded by EURATOM, the UK EPSRC, and US DOE.

NTM and error field proposals slide 2 R J Buttery, NSTX forum, Nov /1 NTM co vs counter rotation dependence DIII-D: shows strong rotation dependence in 2/1 NTM   limit – But what is physics? –Does counter rotation stabilise mode? –Is threshold dependent on rotation shear relative to magnetic shear (á la theory) – Need to test and explore this important result… DIII-D co counter  N (2/1 NTM onset) sawtoothing ELMy H modes

NTM and error field proposals slide 3 R J Buttery, NSTX forum, Nov 2007 counter-co  N (2/1 NTM onset) DIII-D, NSTX n=3 braking study Similar % fall in  N per % Mach 2/1 NTM co vs counter rotation dependence DIII-D: shows strong rotation dependence in 2/1 NTM   limit – But what is physics? –Does counter rotation stabilise mode? –Is threshold dependent on rotation shear relative to magnetic shear (á la theory) – Need to test and explore this important result… NSTX can shed more light on this story… ? EFs?

NTM and error field proposals slide 4 R J Buttery, NSTX forum, Nov 2007 Key issues NSXT can shed light on NSTX can probe error field effects –To see if increased sensitivity at low rotation NSTX can explore rotation profile effects –Distinguish between rotation and rotation shear models? –Assisted by varying mix of n=1 & n=3 braking NSTX can readily address the counter rotation question –Does trend go up or down in counter direction? –Just reverse Bt and Ip… (later, but covered by this XP) Part A Part B Stefan Gerhardt analysis… :  N vs rotation  P vs rotation  P vs rotation shear  N vs rotation shear

NTM and error field proposals slide 5 R J Buttery, NSTX forum, Nov 2007 Part A:

NTM and error field proposals slide 6 R J Buttery, NSTX forum, Nov 2007 counter-co  N (2/1 NTM onset) DIII-D, NSTX n=3 braking study Similar % fall in  N per % Mach Part B (later): counter Bt and Ip scans Recall previous NSTX and DIII-D scans: Simple technique is to reverse Ip and Bt to get strong counter data – Key test of underlying theory governing rotation dependence ? NSTX: about 0.5 shifts, counter B T and I P Apply ramps in  to trigger 2/1 NTM (ref shot ) May need co- comparison, and vary rotation with n=3…