Long Pulse High Performance Plasma Scenario Development for the National Spherical Torus Experiment
Authors: C.E. Kessel, R.E. Bell, M.G. Bell, D.A. Gates, R.W. Harvey, S.M. Kaye, B.P. LeBlanc, T.K. Mau, J.E. Menard, C.K. Phillips, P.M. Ryan, S.A. Sabbagh, E.J. Synakowski, G. Taylor, R. Wilson and the NSTX Research Team
Abstract:
The National Spherical Torus Experiment (NSTX) [Ono, M., et al., Nucl. Fusion, 44, (2004), 452.] is targeting long pulse high performance, non-inductive sustained operations at low aspect ratio, and the demonstration of non-solenoidal start-up and current ramp-up. The modeling of these plasmas provides a framework for experimental planning and identifies the tools to access these regimes. Simulations based on NBI- (Neutral Beam Injection) heated plasmas are made to understand the impact of various modifications, and identify the requirements for 1) high elongation and triangularity, 2) density control to optimize the current drive, 3) plasma rotation and/or feedback stabilization to operate above the no-wall β limit, and 4) Electron Bernstein Waves (EBW) for off-axis heating/current drive (H/CD). Integrated scenarios are constructed to provide the transport evolution and H/CD source modeling, supported by rf (radio frequency) and stability analyses. Important factors include the energy confinement, Zeff, early heating/H-mode, broadening of the NBI-driven current profile, and maintaining q(0) and qmin>1.0. Simulations show that non-inductive sustained plasmas can be reached at IP=800 kA, BT=0.5 T, κ≈2.5, βN≤5, β≤15%, fNI=92%, and q(0)>1.0 with NBI H/CD, density control, and similar global energy confinement to experiments. The non-inductive sustained high β plasmas can be reached at IP=1.0 MA, BT=0.35 T, κ≈2.5, βN≤9, β≤43%, fNI=100%, and q(0)>1.5 with NBI H/CD and 3.0 MW of EBW H/CD, density control, and 25% higher global energy confinement than experiments. A scenario for non-solenoidal plasma current ramp-up is developed using High Harmonic Fast Wave (HHFW) H/CD in the early low IP and low Te phase, followed by NBI H/CD to continue the current ramp, reaching a maximum of 480 kA after 3.4 s.
Published in: Physics of Plasmas 13, 056108 (2006)
doi: 10.1063/1.2177645
© (2006) American Institute of Physics.
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