L-H Threshold Studies in NSTX*

L-H transition experiments in NSTX have been run in support of the high priority ITER and ITPA issue of access to the H-mode. Experiments revealed that the L-H threshold power for helium was 20 to 40{\%} greater than that for deuterium. There was a $\sim $35{\%} reduction in the threshold power for discharges using lithium evaporation. Application of n=3 fields at the plasma edge, potentially critical for suppression of ELMs in ITER, resulted in a 65{\%} increase in threshold power with no change in plasma rotation. Threshold powers were almost a factor of two greater at 1 MA than at 0.7 kA, consistent with calculations from XGC0 showing a deeper E$_{r}$ well and stronger E$_{r}$ shear near the edge at lower current. Low triangularity discharges required lower heating powers to transition into the H-mode, also consistent with XGC0. No systematic differences in T$_{e}$, n$_{e}$, p$_{e}$, T$_{i}$, v$_{\phi}$ or their derivatives between purely L-mode and pre-transition H-mode plasmas were found.