LH and ICRF driven scrape-off-layer density modifications and their impact on LH coupling on Alcator C-Mod

Studies of scrape-off-layer (SOL) density profiles by a reflectometer at three poloidal locations adjacent to the lower hybrid (LH) launcher show that for a wide range of plasma parameters, the application of either LH power only or combined with ion cyclotron range of frequencies (ICRF) power induces large modifications on SOL profiles and also creates strong poloidal density striations. With density striations, calculating LH reflection coefficient assuming a poloidally uniform density profile becomes inadequate to represent experimental conditions. The experimentally measured LH reflection coefficient appears to be close to that calculated using the measured density profile in front of the waveguide mouth, where strong density depletion is observed. Using profiles from other locations can result in a factor of 2 too low in reflection coefficient calculation. The poloidal density striations with LH power can be reproduced by a 2-D diffusive-convective model that includes the dynamics of the LH induced E...