HIGH-PERFORMANCE DISCHARGES IN THE SMALL TIGHT ASPECT RATIO TOKAMAK (START)

The Small Tight Aspect Ratio Tokamak (START) [A. Sykes et al., Nucl. F usion 32, 769 (1994)] spherical tokamak has recently achieved the reco rd value of toroidal beta similar to-30% in a tokamak-like configurati on. The improvements that have made these results possible are present ed along with a description of the global equilibrium parameters of th e discharges. The ideal magnetohydrodynamic (MHD) stability of these d ischarges is analyzed, and they are found to be in close proximity to both the ballooning limit and the external current driven kink limit, but they are found to be far from the pressure driven external kink Li mit. Disruptivity for a range of shots is not correlated with the norm alized beta limit, but does correlate well with the empirical high-l(i ) disruption limit. The transport properties of these high-beta-equili bria are analyzed and compared to conventional tokamak scaling laws an d transport models. The global transport is at least as good as that p redicted by the ITER97-ELMy (edge-localized) scaling law. The local io n transport is in good agreement with that predicted by neoclassical m odels. The electron transport is anomalous, showing rough agreement wi th the Lackner-Gottardi transport model. (C) 1998 American Institute o f Physics.