The Effect of ELMs on HHFW Heating of NBI Generated H‐modes

ELMs reduce the stored energy achieved with HHFW heating compared with the ELM free case as also occurs for NBI heating alone. This reduction can be attributed both to direct ELM ejection of stored energy and to an increase in edge density with ELMs that exceeds the onset density for perpendicular wave propagation near the antenna [1,2], and leads to significantly more edge RF power deposition. This latter effect causes a more intense RF “hot” zone in the lower divertor scrape off region due to an increase in edge RF power propagating to the divertor from the antenna region along the magnetic field lines. Fast IR measurements of the direct ELM heat deposition at the lower divertor shows it to be peaked in the vicinity of the outer strike radius and to fall off strongly as the “hot” zone is approached, indicating little direct ELM effect on the “hot” zone heating. Physics studies of the “hot” zone have begun with sweeping the RF “hot” zone spiral over Rogowski instrumented divertor region tiles to show tha...