Observation of a double-peaked heat flux profile in the SAS-VW divertor

A series of experiments were carried out in the DIII-D SAS-VW divertor to investigate the interplay between divertor behavior, the impact of drifts, and divertor geometry. A double peak structure was observed in both q_// derived from Langmuir probe (LP) measurements and q_⊥ determined from surface eroding thermocouples for both B_T directions with the outer strike point placed at the inner slant of the SAS-VW divertor. With ion directed out of the divertor, particles cross the vertex from the inner slant to the outer target region driven by the ion drift. This results in a considerable flux of particles being redirected from the separatrix to the outer target region in the SAS. The double-peak in the J_sat profile measured by LPs is interpreted as evidence of this drift effect. Alternatively, with ion directed into the divertor, the double peak in the heat flux profile is caused by the separation of electron temperature which is demonstrated by a double-peak in the T_e profile from LP measurements and reproduced by SOLPS modeling. The double-peak in heat flux profile separates the deposited power into two radial bands, in which the second heat flux peak can be as high as ~60% of the first heat flux peak, consequently reducing the maximum heat flux at the strike point.