Triggered confinement and pedestal temperature enhancement in NSTX H-mode discharges*

We report progress in the extension of a high performance regime (``Enhanced Pedestal'' or EP H-mode) in NSTX discharges, where the pedestal temperature doubles and the energy confinement increases by 50{\%}, above and beyond the confinement enhancement from lithium wall coatings [1]. The spontaneous transition is triggered by a large edge-localized mode, either natural or externally triggered by 3-D fields; the EP H-mode itself is ELM-free. The transport barrier grows inward from the edge, with a doubling of both the pedestal pressure width and the spatial extent of steep radial electric field shear. While short EP H-mode phases were previously reported [2], an EP H-mode with duration up to three energy confinement times was recently observed. The normalized beta $\sim $ 6.5 is amongst the highest values sustained in NSTX. Moreover the non-inductive fraction $\sim $ 0.65 is the highest plasma current$\sim $0.9 MA in NSTX. Experiments are continuing for achievement of reproducible EP H-modes. \\[4pt] [1] H.W. Kugel, et. al.,Phys. Plasma \textbf{15} (2008) 056118. \\[0pt] [2] R. Maingi, et. al., J. Nucl. Mater. \textbf{390-391} (2009) 440.