Long Pulse High Performance Plasma Scenario Development for NSTX

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 startup and current rampup. 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 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