H-Mode Turbulence, Power Threshold, ELM, and Pedestal Studies in NSTX

Maingi, R. ; Bush, C.E. ; Fredrickson, E.D. ; Gates, D.A. ; Kaye, S.M. ; LeBlanc, B.P. ; Menard, J.E. ; Meyer, H. ; Mueller, D. ; Nishino, N. ; Roquemore, A.L. ; Sabbagh, S.A. ; Tritz, K. ; Zweben, S.J. ; Bell, M.G. ; Bell, R.E. ; Biewer, T. ; Boedo, J.A. ; Johnson, D.W. ; Kaita, R. ; Kugel, H.W. ; Maqueda, R.J. ; Munsat, T. ; Raman, R. ; Soukhanovskii, V.A. ; Stevenson, T. ; Stutman, D.

Princeton University. Plasma Physics Laboratory.

关键词: Heating;    Bootstrap Current;    70 Plasma Physics And Fusion Technology;    Tokamaks, Nstx;    Edge Plasma;   

DOI  :  10.2172/836092
RP-ID  :  PPPL-4016
RP-ID  :  AC02-76CH03073
RP-ID  :  836092

美国|英语

来源: UNT Digital Library

【 摘 要 】

High-confinement mode (H-mode) operation plays a crucial role in NSTX [National Spherical Torus Experiment] research, allowing higher beta limits due to reduced plasma pressure peaking, and long-pulse operation due to high bootstrap current fraction. Here, new results are presented in the areas of edge localized modes (ELMs), H-mode pedestal physics, L-H turbulence, and power threshold studies. ELMs of several other types (as observed in conventional aspect ratio tokamaks) are often observed: (1) large, Type I ELMs, (2) ''medium'' Type II/III ELMs, and (3) giant ELMs which can reduce stored energy by up to 30% in certain conditions. In addition, many high-performance discharges in NSTX have tiny ELMs (newly termed Type V), which have some differences as compared with ELM types in the published literature. The H-mode pedestal typically contains between 25-33% of the total stored energy, and the NSTX pedestal energy agrees reasonably well with a recent international multi-machine scaling. We find that the L-H transition occurs on a {approx}100 {micro}sec timescale as viewed by a gas puff imaging diagnostic, and that intermittent quiescent periods precede the final transition. A power threshold identity experiment between NSTX and MAST shows comparable loss power at the L-H transition in balanced double-null discharges. Both machines require more power for the L-H transition as the balance is shifted toward lower single null. High field side gas fueling enables more reliable H-mode access, but does not always lead to a lower power threshold e.g., with a reduction of the duration of early heating. Finally the edge plasma parameters just before the L-H transition were compared with theories of the transition. It was found that while some theories can separate well-developed L- and H-mode data, they have little predictive value.