Initial Studies of Core and Edge Transport of NSTX Plasmas
Authors: E.J. Synakowski, M.G. Bell, R.E. Bell, C.E. Bush, C. Bourdelle, D. Darrow, W. Dorland, A. Ejiri, E.D. Fredrickson, D.A. Gates, S.M. Kaye, S. Kubota, H.W. Kugel, B.P. LeBlanc, R. Maingi, R.J. Maqueda, J.E. Menard, D. Mueller, A. Rosenberg, S.A. Sabbagh, D. Stutman, G. Taylor, D.W. Johnson, R. Kaita, M. Ono, F. Paoletti, W. Peebles, Y-K.M. Peng, A.L. Roquemore, C.H. Skinner, V.A. Soukhanovskii, and the NSTX Research Team
Date of PPPL Report: September 2001
Presented at: the IAEA Technical Committee Meeting on H-Mode Physics and Transport Barriers, in Toki, Japan, September 5-7, 2001. To be published in a Special Issue of Plasma Physics and Controlled Fusion.
Rapidly developing diagnostic, operational, and analysis capability is enabling the first detailed local physics studies to begin in high beta plasmas of the National Spherical Torus Experiment (NSTX). These studies are motivated in part by energy confinement times in neutral-beam-heated discharges that are favorable with respect to predictions from the ITER-89P scaling expression. Analysis of heat fluxes based on profile measurements with neutral-beam injection (NBI) suggest that the ion thermal transport may be exceptionally low, and that electron thermal transport is the dominant loss channel. This analysis motivates studies of possible sources of ion heating not presently accounted for by classical collisional processes. Gyrokinetic microstability studies indicate that long wavelength turbulence with kqri ~ 0.1-1 may be suppressed in these plasmas, while modes with kqri ~ 50 may be robust. High harmonic fast wave (HHFW) heating efficiently heats electrons on NSTX, and studies have begun using it to to assess transport in the electron channel. Regarding edge transport, H-mode transitions occur with either NBI or HHFW heating. The power required for L-to H-mode transitions far exceeds that expected from empirical ELM-free H-mode scaling laws derived from moderate aspect ratio devices. Finally, initial fluctuation measurements made with two techniques are permitting the first characterizations of edge turbulence.