Effects of ICRF and LHCD on SOL Density Profiles on Alcator C-Mod

A swept‐frequency X‐mode reflectometer has being installed on Alcator C‐Mod to measure the SOL density profiles at three poloidal locations adjacent to the new Lower Hybrid Launcher. First results on density profile modifications at the LH launcher due to ICRH or LHCD non‐linear effects will be presented. Experimental measurements indicate that the application of LH power creates a density depletion near the LH launcher, which is consistent with the influence of a ponderomotive force. At high ne, LH power increases the density in the far SOL. Application of low ICRF power decreases the density in front of the LH launcher, which may be consistent with ICRF sheath induced convective cells. Preliminary results, however, indicate that field line mapping and increasing ICRF power do not modify the density profile significantly.