Study of non-axisymmetric divertor footprints using 2-D IR and visible cameras and a 3-D heat conduction solver in NSTX

Abstract

Toroidally non-axisymmetric divertor profiles during the 3-D field application and for ELMs are studied with simultaneous observation by a new wide angle visible camera and a high speed IR camera. A newly implemented 3-D heat conduction code, TACO, is used to obtain divertor heat flux. The wide angle camera data confirmed the previously reported result on the validity of vacuum field line tracing on the prediction of split strike point pattern by 3-D fields as well as the phase locking of ELM heat flux to the 3-D fields. TACO calculates the 2-D heat flux distribution allowing assessment of toroidal asymmetry of peak heat flux and heat flux width. The degree of asymmetry (εDA) is defined to quantify the asymmetric heat deposition on the divertor surface and is found to have a strong positive dependence on peak heat flux.