Characteristics of the First H-mode Discharges in NSTX
Authors: R. Maingi, M.G. Bell, R.E. Bell, C.E. Bush, E.D. Fredrickson, D.A. Gates, S.M. Kaye, H.W. Kugel, B.P. LeBlanc, J.E. Menard, D. Mueller, S.A. Sabbagh, D. Stutman, G. Taylor, D.W. Johnson, R. Kaita, R.J. Maqueda, M. Ono, F. Paoletti, Y-K.M. Peng, A.L. Roquemore, C.H. Skinner, V.A. Soukhanovskii, and E.J. Synakowski
Date of PPPL Report: May 2001
Submitted to: Physical Review Letters
We report observations of the first low-to-high (L-H) confinement mode transitions in the National Spherical Torus Experiment (NSTX). The H-mode energy confinement time increased over reference L-mode discharges transiently by 100-300%, as high as approximately 150 ms. This confinement time is approximately 1.8-2.3 times higher than predicted by a multi-machine ELM-free H-mode scaling. This achievement extends the H-mode window of fusion devices down to a record low aspect ratio (R/a) ~ 1.3, challenging both confinement and L-H power thresholds scalings based on conventional aspect ratio tokamaks.