| Autor: |
Akers, R. J., Ahn, J. W., Appel, L. C., Arends, E. R., Axon, K. B., Buttery, R. J., Byrom, C., Carolan, P. G., Counsell, G. F., Cunningham, G., Ciric, D., Conway, N. J., Dowling, J., Field, A. R., Fielding, S. J., Gee, S., Gryaznevich, M. P., Hole, M., Kirk, A., Lehane, I. |
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| Zdroj: |
Physics of Plasmas; Sep2002, Vol. 9 Issue 9, p3919, 11p |
| Abstrakt: |
Spontaneous transitions from the low "L-mode" to high "H-mode" of tokamak plasma confinement, first observed during neutral beam heating experiments on ASDEX, are now routinely achieved in many tokamak experiments. The H-mode regime is attractive as it offers the possibility of enhanced confinement, and thus a route towards a more "compact" and cost-efficient fusion power-plant. Transition to H-mode is now routinely achievable in the Mega-Amp Spherical Tokamak (MAST) [A. C. Darke et al., Fusion Technology 1994 (Elsevier, Amsterdam, 1995), Vol. 1, p. 799] for both Ohmically and neutral beam injection (NBI) heated plasmas (P[sub NBI] ∼0.5-1.7 MW). H-mode plasmas can be either center stack limited or X-point diverted, exhibiting regular Type III edge localized modes (ELMs). Global confinement in H-mode with low frequency ELMs is consistent with the international IPB(y,2) scaling and exceeds the scaling by a factor ∼ 1.5-2.0 for high performance discharges. Confinement degrades with increasing ELM frequency (which in turn scales with power and density) as for conventional tokamaks. Densities above the Greenwald limit (G ∼ 1) have been achieved for plasma currents up to 0.8 MA using gas-fueling, and up to 0.9 MA using a low field side multi-pellet injector. High field side fueling, on the other hand, can be supplied via a gas-feed located at the center-column mid-plane, this technique having been found to dramatically enhance H-mode accessibility and quality. When combined with Connected Double Null plasma topology, a significant reduction in Ohmic L-H power threshold can be achieved; as a result, power threshold data are now in broad agreement with a number of the latest scaling law predictions. Following the transition to H-mode, power crossing the inner separatrix remains low, resulting in a high recycling scrape-off layer (compared with partial detachment in L-mode). To date, with NBI power limited to 1.7 MW, H-mode MAST plasmas have shown no... [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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