Overview of NSTX Upgrade Initial Results and Modelling Highlights
J. Menard et al.
57 (2017) 102006 (17pp)
Abstract
|
|
The National Spherical Torus Experiment (NSTX) has undergone a major
upgrade, and the NSTX Upgrade (NSTX-U) Project was completed in the
summer of 2015. NSTX-U rst plasma was subsequently achieved, diagnostic
and control systems have been commissioned, the H-mode accessed,
magnetic error elds identi ed and mitigated, and the first physics
research campaign carried out. During ten run weeks of operation, NSTX-U
surpassed NSTX record pulse-durations and toroidal fields (TF), and
high-performance ~1 MA H-mode plasmas comparable to the best of NSTX
have been sustained near and slightly above the n = 1 no-wall stability
limit and with H-mode confinement multiplier H98y,2 above 1. Transport
and turbulence studies in L-mode plasmas have identified the coexistence
of at least two ion-gyro-scale turbulent micro-instabilities near the
same radial location but propagating in opposite (i.e. ion and electron
diamagnetic) directions. These modes have the characteristics of
ion-temperature gradient and micro-tearing modes, respectively, and the
role of these modes in contributing to thermal transport is under active
investigation. The new second more tangential neutral beam injection was
observed to significantly modify the stability of two types of Alfven
eigenmodes. Improvements in of ine disruption forecasting were made in
the areas of identification of rotating MHD modes and other macroscopic
instabilities using the disruption event characterization and forecasting
code. Lastly, the materials analysis and particle probe was utilized on
NSTX-U for the first time and enabled assessments of the correlation
between boronized wall conditions and plasma performance. These and other
highlights from the first run campaign of NSTX-U are described.