Experimental survey of the L-H transition conditions in the DIII-D tokamak

We present the global analysis of a recent survey of the H-mode power threshold in DIII-D using D degrees to D+ NBI after boronization of the vacuum vessel. Single parameter scans of BT, Ip, density, and plasma shape have been carried out on the DIII-D tokamak for neutral beam heated single-null and double-null diverted plasmas. In single-null discharges, the power threshold is found to increase approximately linearly with BT and ne but remains independent of Ip. In double-null discharges, the power threshold is found to be approximately independent of both BT and ne. Various shape parameters such as plasma-wall gaps had only a weak effect on the power threshold. Imbalancing the double null configuration resulted in a large increase in the threshold power.