Identifying the Location of the Separatrix at the OMP in DIII-D Using Power Accounting

Two methods are used which employ power accounting to improve the accuracy of identifying R-sep-omp, the location of the separatrix at the outside midplane (omp). The first method uses the measured deposited power profile at the outer target as the primary input, the P-SOL-exhaust method. The other uses the measured power input to the SOL, obtained from the total heating power less the power radiated from inside the separatrix, the P-SOL-input method. The methods were applied to experimental data for 21 H-mode DIII-D discharges. High spatial resolution Thomson scattering measured profiles of between-ELM $n_e$ and $T_e$ were used to calculate the electron parallel conducted heat flux profile which was then matched to the measured P-SOL-exhaust and P-SOL-input by adjusting R-sep-omp relative to that of the Thomson data. The values of R-sep-omp from the 2 methods agree to within $\sim$1 mm of each other and to within $\sim$1 mm of the values given by the ``standard DIII-D method'' [1]. This results in only modest changes to $n_e$ and $T_e$ at R-sep-omp relative to the ``standard'' values, increasing $n_e$ by $\sim$10\% and $T_e$ by $\sim$20\%.\par \vskip6pt \noindent[1] G.D. Porter et al., Phys. Plasmas 5, 1410 (1998).