Abstract
The National Spherical Torus Experiment (NSTX) has made considerable progress in advancing the scientific
understanding of high performance long-pulse plasmas needed for future spherical torus (ST) devices and ITER.
Plasma durations up to 1.6 s (five current redistribution times) have been achieved at plasma currents of 0.7MA
with non-inductive current fractions above 65% while simultaneously achieving βT and βN values of 17% and 5.7
(%mTMA−1), respectively. A newly available motional Stark effect diagnostic has enabled validation of currentdrive
sources and improved the understanding of NSTX ‘hybrid’-like scenarios. In MHD research, ex-vessel radial
field coils have been utilized to infer and correct intrinsic EFs, provide rotation control and actively stabilize the
n = 1 resistive wall mode at ITER-relevant low plasma rotation values. In transport and turbulence research,
the low aspect ratio and a wide range of achievable β in the NSTX provide unique data for confinement scaling
studies, and a new microwave scattering diagnostic is being used to investigate turbulent density fluctuations with
wavenumbers extending from ion to electron gyro-scales. In energetic particle research, cyclic neutron rate drops
have been associated with the destabilization of multiple large toroidal Alfven eigenmodes (TAEs) analogous to
the ‘sea-of-TAE’ modes predicted for ITER, and three-wave coupling processes have been observed for the first
time. In boundary physics research, advanced shape control has enabled studies of the role of magnetic balance in
H-mode access and edge localized mode stability. Peak divertor heat flux has been reduced by a factor of 5 using an
H-mode-compatible radiative divertor, and lithium conditioning has demonstrated particle pumping and results in
improved thermal confinement. Finally, non-solenoidal plasma start-up experiments have achieved plasma currents
of 160 kA on closed magnetic flux surfaces utilizing coaxial helicity injection.