Abstract

We report the dependence of the lower divertor surface heat flux profiles, measured from infrared thermography and mapped magnetically to the mid-plane on loss power into the scrape-off layer (PLOSS), plasma current (Ip), and magnetic flux expansion (fexp), as well as initial results with lithium wall conditioning in NSTX. Here we extend previous studies [R. Maingi et al., J. Nucl. Mater. 363–365 (2007) 196–200] to higher triangularity ∼0.7 and higher Ip⩽1.2MA. First we note that the mid-plane heat flux width mapped to the mid-plane, λqmid, is largely independent of PLOSS for PLOSS⩾4MW. λqmid is also found to be relatively independent of fexp; peak heat flux is strongly reduced as fexp is increased, as expected. Finally, λqmid is shown to strongly contract with increasing Ip such that λqmid∝Ip-1.6 with a peak divertor heat flux of qdiv, peak∼15MW/m2 when Ip=1.2MA and PLOSS∼6MW. These relationships are then used to predict the divertor heat flux for the planned NSTX-Upgrade, with heating power between 10 and 15MW, Bt=1.0T and Ip=2.0MA for 5s.

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