Overview of NSTX Upgrade initial results and modelling highlights

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 first plasma was subsequently achieved, diagnostic and control systems have been commissioned, the H-mode accessed, magnetic error fields identified 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 offline 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.

Effect of deuterium irradiation on graphite boronized in the NSTX-U tokamak

“…The National Spherical Torus Experiment Upgrade (NSTX-U) is a spherical tokamak with carbon-based PFC 12–14 . During the FY2016 experimental campaign, boronization was used as the main PFC conditioning technique in NSTX-U 13,15 . Boron was deposited using a DC glow of He and deuterated Trimethyl boron (d-TMB) 15 .…”

Plasma boundary shape control and real-time equilibrium reconstruction on NSTX-U

“…The National Spherical Torus eXperiment Upgrade facility (NSTX-U) [1], which completed its first plasma operation campaign in 2016 [2,3], aims to span between the previous class of spherical torus devices, like NSTX [4] or the megaampere spherical tokamak (MAST) [5], and future facilities planned to study plasma-material interaction [6], nuclear comp onents [7], and demonstration of fusion power production [8,9]. NSTX-U looks to build upon the results of NSTX [10] to improve the physics understanding of several key issues for future devices, including the scaling of electron transport with field and current [11][12][13][14], the physics of fast particles [15][16][17][18], and the achievement and sustainment of non-inductive, high-β scenarios [19][20][21][22][23][24].…”

UKAEA capabilities to address the challenges on the path to delivering fusion power

“…The main UKAEA facilities existing and in development are: JET [1], the world's largest and most capable fusion facility today, capable of using tritium, is operated by the UK for exploitation as a key part of the EUROfusion roadmap to fusion electricity (). JET is a model for ITER [2] and is the best facility to mitigate risks ahead of ITER operation.MAST Upgrade [4,8], together with NSTX-U [9], are the world's largest ‘spherical’ tokamaks. MAST Upgrade has unique features focused on the exhaust issue, challenge (ii), and will be developed and exploited with EUROfusion.…”

“…JET is a model for ITER [2] and is the best facility to mitigate risks ahead of ITER operation. -MAST Upgrade [4,8], together with NSTX-U [9], are the world's largest 'spherical' tokamaks. MAST Upgrade has unique features focused on the exhaust issue, challenge (ii), and will be developed and exploited with EUROfusion.…”