Investigation of the triggering mechanism for internal transport barriers in Alcator C-Mod.

Internal transport barriers (ITBs) can be routinely produced in C-Mod steady enhanced D$_{\alpha }$ (EDA) H-mode plasmas by applying ICRF at $\vert $r/a$\vert \quad \ge $ 0.5 (off-axis heating). The triggering mechanism of these ITBs is under consideration. The importance of the magnetic shear and the critical scale length a/L$_{T}$ are being explored. Preliminary results from TRANSP analysis suggest that the ITB triggering could depend on the magnetic shear. At the same time a/L$_{T}$, which has been seen to decrease as the ICRF resonance position is moved outward by raising the magnetic field, is likely to play a role in suppressing ITG turbulence. These effects are studied using a kinetically constrained EFIT model as well as the gyrokinetic code GS2. Recent experimental results as well as the results from the analysis will be presented.