L-H Mode Transitions in the National Spherical Torus Experiment
Edge data from plasmas in the National Spherical Torus Experiment (NSTX) [S. Kaye et al., Fusion Technology 36 (1999) 16] have been compared to theories of transport suppression that have been used to develop a physics framework for low-confinement (L) to high-confinement (H) mode transitions. The NSTX data were obtained in low aspect ratio (R/a approximately equal to 1.3) discharges taken from a variety of discharge phases, including L-modes, L-H transitions, and H-modes with and without edge localized modes (ELMs). The comparisons show that the group of points taken just before the L-H mode transition are well mixed with the purely L-mode group to within the measurement uncertainties, indicating that changes in these parameters leading up to the transition are subtle. One of the theory parameters, alpha{sub MHD} = -R{sub q}{sup 2}dbeta{sub t/dr}, does show a clear threshold alpha{sub MHD} = 1 to 2 between the H-mode grouping of points and those remaining in the L-mode or taken just prior to the transition. Additionally, there is no evidence for an edge temperature threshold necessary for transitioning into the H-mode. NSTX data indicate further a possible connection between L-H transitions and non-ambipolar beam ion losses.
- Research Organization:
- Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC) (US)
- DOE Contract Number:
- AC02-76CH03073
- OSTI ID:
- 814726
- Report Number(s):
- PPPL-3745; TRN: US0304330
- Resource Relation:
- Other Information: PBD: 24 Jul 2003
- Country of Publication:
- United States
- Language:
- English
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