Dependence of divertor heat flux widths on heating power, flux expansion, and plasma current in the NSTX

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 (P-LOSS), plasma current (I-p), and magnetic flux expansion (f(exp)), 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 similar to 0.7 and higher I-p <= 1.2 MA. First we note that the mid-plane heat flux width mapped to the mid-plane, lambda(mid)(q) is largely independent of P-LOSS for P-LOSS >= 4 MW. lambda(mid)(q) is also found to be relatively independent of f(exp); peak heat flux is strongly reduced as f(exp) is increased, as expected. Finally, lambda(mid)(q) is shown to strongly contract with increasing I-p such that lambda(mid)(q) alpha I-p(-1.6) with a peak divertor heat flux of q(div), (peak) similar to 15 MW/m(2) when I-p = 1.2 MA and P-LOSS similar to 6 MW. These relationships are then used to predict the divertor heat flux for the planned NSTX-Upgrade, with heating power between 10 and 15 MW, B-t = 1.01 and I-p= 2.0 MA for 5 s. (C) 2011 Elsevier B.V. All rights reserved.