Analysis of Lower Hybrid Current Drive Modification of Sawtooth in Alcator C-Mod

Experiments were performed in Alcator C-Mod, where the onset time for sawteeth was delayed significantly (up to 0.5 s) relative to ohmically heated plasmas, through the injection of off-axis LH current drive power [1]. The LH driven current density profiles in these experiments are being simulated using a ray tracing code (GENRAY) and Fokker Planck code (CQL3D) [2] in order to ascertain the consistency of the simulated current density profiles with the requirements for sawtooth stabilization. Comparisons of simulated LHRF-generated hard x-ray spectra with experimental measurements will be shown. We will also discuss time dependent simulations of these experiments using an advanced parallel computing framework [3]. \\[4pt] [1] C. E. Kessel \textit{et al}, Bull. of the Am. Phys. Soc. \textbf{53}, Poster PP6.00074 (2008). \\[0pt] [2] R. W. Harvey and M. G. McCoy, Proc. of the IAEA Tech. Comm. Mtg on Sim. and Mod. of Therm. Plasmas, Montreal, Canada (1992). \\[0pt] [3] D. Batchelor \textit{et al}, J. of Phys. Conf. Series \textbf{125}, 012039 (2008).