NTM Stability at Low Collisionality J. A. Snipes, T. C. Hender*, S. M. Wolfe MIT Plasma Science and Fusion Center, Cambridge, MA USA *UKAEA-Euratom, Culham Science Centre, Culham, UK J A Snipes, Alcator C-Mod Ideas Forum, MIT PSFC, Cambridge, MA 13 – 15 December 2006

Can we Approach NTM Stability Limits at Low *? Previous NTM threshold scalings on DIII-D and AUG indicated C-Mod approaches the NTM threshold  Recent JET scalings differ: C-Mod is still far from the N scaling C-Mod surpasses the p scaling without NTM's J A Snipes, Alcator C-Mod Ideas Forum, MIT PSFC, Cambridge, MA 13 – 15 December 2006

NTM Stability at Low Collisionality Motivation: C-Mod’s unique operational range can help distinguish between various NTM threshold dimensionless scalings through multi-machine comparisons (JET, DIII-D, AUG). This will be important to correctly predict NTM stability in ITER. Goals: Operate at high  and low collisionality to approach or surpass the various NTM threshold scalings. Look for unstable low frequency MHD activity and try to distinguish NTMs from classical modes. Plan of execution: Begin with 1001013016 then reduce the density • Use the divertor cryopump to maintain density control at low density • Will require PICRF > 4 MW preferably up to 6 MW • Use DNB to measure q(r) with MSE to determine the MHD  • Scan ne down to 4  1020 m-3 to cross * NTM threshold scalings • Scan Ip to vary the p scaling more than the N scaling to further distinguish the two scalings ~ J A Snipes, Alcator C-Mod Ideas Forum, MIT PSFC, Cambridge, MA 13 – 15 December 2006