LHCD during current ramp experiments on Alcator C-Mod
Author(s)Poli, F.; Scott, S.D.; Wallace, Gregory Marriner; Chilenski, Mark Alan; Hughes Jr, Jerry; Mumgaard, Robert Thomas; Shiraiwa, Shunichi; Wukitch, Stephen James; ... Show more Show less
MetadataShow full item record
The lower hybrid current drive (LHCD) system on Alcator C-Mod is capable of sustaining fully non-inductive discharges for multiple current relaxation times (τ cr ∼ 200 ms) at line averaged densities in the range of 5x10 19 m -3 . Some of these non-inductive discharges develop unstable MHD modes that can greatly reduce current drive performance, particularly in discharges with plasma current of 0.5 MA or less [1,2]. Avoiding these unstable MHD modes motivated an experiment to test if the stable current profile shape of a higher current non-inductive discharge could be achieved in a lower current discharge. Starting from a discharge at 0.8 MA, the plasma current was ramped down to 0.5 MA over 200 ms. The surface voltage of the plasma swings negative during the ramp, with the loop voltage reversal impacting the edge fast electron measurements immediately. Little change can be seen during the I p ramp in the core fast electron measurements, indicating that the loop voltage reversal does not penetrate fully to the magnetic axis on the timescale of the current ramp. The resulting discharge did not exhibit deleterious MHD instabilities, however the existence of this one discharge does not necessarily represent a robust solution to the problem.
DepartmentMassachusetts Institute of Technology. Plasma Science and Fusion Center
EPJ Web of Conferences
Wallace, G.M. et al. “LHCD During Current Ramp Experiments on Alcator C-Mod.” Edited by J. Hillairet. EPJ Web of Conferences 157 (2017): 03063 © 2017 The Authors, published by EDP Sciences
Final published version