Abstract
The National Spherical Torus Experiment (NSTX) at Princeton University, Princeton, NJ, is designed to assess the potential of the low-aspect-ratio spherical torus concept for magnetic
plasma confinement. The plasma has been heated by up to 7 MW
of neutral beam injection (NBI) at an injection energy of 100 keV
and up to 6 MW of high harmonic fast wave (HHFW) at 30 MHz.
NSTX has achieved of 32%. A variety of MHD phenomena
have been observed to limit . NSTX has now begun addressing
scaling, limits, and current drive issues. During the NBI heating
experiments, a broad profile with up to 2 keV, and
a large toroidal rotation were observed. Transport analysis suggests
that the impurity ions have diffusivities approaching neoclassical.
For L-Mode plasmas, is up to two times the ITER97L
L-Mode scaling and exceeds the ITER98pby2 H-Mode scaling in
some cases. Transitions to H-Mode have been observed which result
in an approximate doubling of after the transition in some
conditions. During HHFW heating, and up to 3.5 keV
were observed. Current drive has been studied using both coaxial
helicity injection with up to 390 kA of toroidal current and HHFW.
HHFW has produced H-modes with significant bootstrap current
fraction at low , high , and high .