Alcator C-Mod experiments in support of the ITER baseline 15 MA scenario

Experiments on Alcator C-Mod from 2009–2012 have examined the rampup, flattop and rampdown phases of the proposed ITER 15 MA baseline scenario. Rampup studies show ICRF heating can significantly reduce the V-s requirement, and that an H-mode late in the ramp can reduce this further. ICRF modifications to l i in L-mode are minimal, although the T e profile is peaked relative to ohmic in the plasma centre, and reduces the sawtooth onset times. Flattop plasmas targeting ITER baseline parameters have been sustained for 20 τ E or 8 − 13 τ CR , but only reach H 98 ∼ 0.6 at n / n Gr = 0.85, rising to 0.9 at n / n Gr = 0.65. Rampdown studies show H-modes can be routinely sustained with ICRF power injection, avoiding an OH coil over-current associated with the H–L transition. In addition, faster current rampdowns are preferred to avoid an over-current when an H–L transition ultimately does occur. In the H-mode rampdown the density is found to drop with I p , preserving the n / n Gr ratio, so long as ICRF power is injected.