Overview of Recent Progress in Understanding NSTX and NSTX-U Plasmas
S.M. Kaye, J.E. Menard, (E. Schuster), et al. (Collaboration Paper)
27th IAEA Fusion Energy Conference
Gandhinagar, India, October 22-27, 2018
Abstract
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The mission of the spherical tokamak NSTX-U is to explore the physics
that drives core and pedestal transport and stability at high-β and
low collisionality, as part of the development of the ST concept towards
a compact, low-cost ST-based Pilot Plant. NSTX-U will ultimately operate
at up to 2 MA and 1 T with up to 10 MW of Neutral Beam Injection (NBI)
power for 5 seconds. NSTX-U will operate in a regime where electromagnetic
instabilities are expected to dominate transport, and beam-heated NSTX-U
plasmas will explore energetic particle (EP) parameter space that is
relevant for both α-heated conventional and low aspect ratio burning
plasmas. NSTX-U will also develop the physics understanding and control
tools to ramp-up and sustain high performance plasmas in a
fully-noninductive fashion. NSTX-U began research operations in 2016,
but a failure of a divertor magnetic field coil resulted in the suspension
of operations and initiation of Recovery activities. During this period,
there has been considerable work in the area of analysis, theory and
modeling with a goal of understanding the underlying physics to develop
predictive models that can be used for high- confidence projections for
both ST and higher aspect ratio regimes. The studies have addressed
issues in thermal plasma transport, EP-driven instabilities at
ion-cyclotron frequencies and below, macrostability, and edge and
divertor physics.