Progress in LHCD modeling and experiments towards the AT regime on Alcator C-Mod.

Electron internal transport barrier (ITB) formation is observed during fully non-inductive LHCD discharges on Alcator C-Mod. The formation is characterized by an abrupt increase of the central electron temperature after a few current penetration time has passed following LHCD turn-on. The ITB phase is often terminated by m = 2 mode activity. Kinetic equilibrium reconstruction and TRANSP/LSC analysis show shear reversal in the q profile during the ITB phase. TRANSP/LSC predictive analysis suggests that f_Bs∼60% is possible if a similar temperature gradient is maintained at r/a∼0.5 with H-factor of 1. [ABSTRACT FROM AUTHOR]