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Progress in Developing Advanced Spherical Tokamak Scenarios in NSTX

Author: Stefan P Gerhardt
Requested Type: Consider for Invited
Submitted: 2009-12-04 14:06:38

Co-authors: S.P. Gerhardt, D. Gates, M. Bell, R. Bell, R. Kaita, E. Kolemen, H. Kugel, B.P. LeBlanc, R. Maingi, J. Menard, S. Sabbagh, H. Yuh

Contact Info:
Princeton Plasma Physics Laboratory
PO Box 451
Princeton, NJ   08543
USA

Abstract Text:
NSTX plasmas with high elongation (~2.7) and triangularity (0.8) have been developed in two regimes: a high beta-poloidal regime focused on understanding the parameter requirements for a near fully-bootstrapped ST-reactor, and a high normalized current regime of relevance to an ST-CTF type device. In both cases, the discharges were aided not only by the extreme shaping, but also confinement improvements from lithium surface conditioning and combined n=1 dynamic error field correction and resistive wall mode feedback. In the first class of plasmas, pulse average poloidal-betas greater than 1.5 have been achieved in a highly reproducible scenario. These discharges have the lowest average surface voltage (~0.15 V) of any discharge type in NSTX and have non-inductive current fractions in the range of 65-70%. The second discharge scenario, operating at higher plasma current and lower toroidal magnetic field, has achieved sustained periods of toroidal beta in excess of 25%, at high betaN and low internal inductance. The role of important NSTX tools in achieving these regimes will be discussed, including in particular the effects of lithium surface coatings. Future additions to these discharge scenarios include inclusion of beta-control via modulation of neutral beams, improved X-point height and boundary control, and, most importantly, reduced density and collisionality due to pumping from the Liquid Lithium Divertor (LLD).

Characterization: A2,A3

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