Heat flux scaling experiments in NSTX

Abstract We report the first results of heat flux scaling experiments in National Spherical Torus Experiment (NSTX). We find that the peak heat flux observed in the outer divertor was ∼6 MW/m2 at 5 MW heating power in lower-single-null diverted configuration. The peak heat flux was observed to increase with heating power, and the highest heat fluxes had narrow profile widths. The peak heat flux is lower than predicted by early 2-D edge transport conservative design calculations. However, the total power flow to the divertor is only 15–30% of the input power, suggesting other processes reduce the available open field line power which can be conducted and convected to the target.