Overview of Recent Physics Results from the National Spherical Torus Experiment (NSTX)
Authors: J.E. Menard, M.G. Bell, R.E. Bell, S. Bernabei, J. Bialek, T. Biewer, and W. Blanchard, et al.
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 1.6s (5 current redistribution times) have been achieved at plasma currents of 0.7 MA with non-inductive current fractions above 65% while simultaneously achieving βT and βN values of 17% and 5.7 (%m·T/MA), respectively. A newly available Motional Stark Effect diagnostic has enabled validation of current drive 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 error fields, 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 wide range of achievable β in NSTX are providing unique data for confinement scaling studies, and a new microwave scattering diagnostic is investigating 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 Alfvén Eigenmodes (TAEs) similar 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 ELM 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 160kA on closed magnetic flux surfaces utilizing Coaxial Helicity Injection.
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Published in 2007 Nuclear Fusion 47, 10 S645–S657
© 2007 Institute of Physics.
doi:10.1088/0029-5515/47/10/S13
Download PPPL-4211 (Preprint Jan 2007; pdf 1.9 MB)