The scaling of the heat flux width in DIII-D

A cross machine analysis of heat flux profile measurements has produced a particularly simple scaling law for the scrape-off-layer (SOL) width, going as Bp,mpe with e ∼ −1.0 where Bp,mp is the poloidal magnetic field at the outer midplane separatrix. This result is in very good agreement with a model based on drift-induced transport. We are also developing a model that extends the kinetic ballooning mode pedestal paradigm to the separatrix and into the SOL. We have calculated the critical pressure gradient at the separatrix using the BALOO code and found that it scales proportionately with the measured pressure gradient. Using an improved high rep-rate and higher edge resolution Thomson scattering system on DIII-D, it is now possible to make detailed comparisons of SOL profile characteristics with the heat flux profile. We find that a two-point flux-limited model is in better agreement with measurements than a conduction-limited model.