517 research outputs found
Overview of the NSTX Control System
The National Spherical Torus Experiment (NSTX) is an innovative magnetic
fusion device that was constructed by the Princeton Plasma Physics Laboratory
(PPPL) in collaboration with the Oak Ridge National Laboratory, Columbia
University, and the University of Washington at Seattle. Since achieving first
plasma in 1999, the device has been used for fusion research through an
international collaboration of over twenty institutions. The NSTX is operated
through a collection of control systems that encompass a wide range of
technology, from hardwired relay controls to real-time control systems with
giga-FLOPS of capability. This paper presents a broad introduction to the
control systems used on NSTX, with an emphasis on the computing controls, data
acquisition, and synchronization systems.Comment: 3 PDF pages, 8th International Conference on Accelerator and Large
Experimental Physics Control Systems (PSN TUBT004), San Jose, CA, USA,
November 27-3
Ideal magnetohydrodynamic simulations of unmagnetized dense plasma jet injection into a hot strongly magnetized plasma
We present results from three-dimensional ideal magnetohydrodynamic
simulations of unmagnetized dense plasma jet injection into a uniform hot
strongly magnetized plasma, with the aim of providing insight into core fueling
of a tokamak with parameters relevant for ITER and NSTX (National Spherical
Torus Experiment). Unmagnetized dense plasma jet injection is similar to
compact toroid injection but with much higher plasma density and total mass,
and consequently lower required injection velocity. Mass deposition of the jet
into the background appears to be facilitated via magnetic reconnection along
the jet's trailing edge. The penetration depth of the plasma jet into the
background plasma is mostly dependent on the jet's initial kinetic energy, and
a key requirement for spatially localized mass deposition is for the jet's
slowing-down time to be less than the time for the perturbed background
magnetic flux to relax due to magnetic reconnection. This work suggests that
more accurate treatment of reconnection is needed to fully model this problem.
Parameters for unmagnetized dense plasma jet injection are identified for
localized core deposition as well as edge localized mode (ELM) pacing
applications in ITER and NSTX-relevant regimes.Comment: 16 pages, 8 figures and 2 tables; accepted by Nuclear Fusion (May 11,
2011
Overview of NSTX Upgrade initial results and modelling highlights
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 similar to 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 H-98y,H-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
Comparison of BES measurements of ion-scale turbulence with direct, gyrokinetic simulations of MAST L-mode plasmas
Observations of ion-scale (k_y*rho_i <= 1) density turbulence of relative
amplitude dn_e/n_e <= 0.2% are available on the Mega Amp Spherical Tokamak
(MAST) using a 2D (8 radial x 4 poloidal channel) imaging Beam Emission
Spectroscopy (BES) diagnostic. Spatial and temporal characteristics of this
turbulence, i.e., amplitudes, correlation times, radial and perpendicular
correlation lengths and apparent phase velocities of the density contours, are
determined by means of correlation analysis. For a low-density, L-mode
discharge with strong equilibrium flow shear exhibiting an internal transport
barrier (ITB) in the ion channel, the observed turbulence characteristics are
compared with synthetic density turbulence data generated from global,
non-linear, gyro-kinetic simulations using the particle-in-cell (PIC) code
NEMORB. This validation exercise highlights the need to include increasingly
sophisticated physics, e.g., kinetic treatment of trapped electrons,
equilibrium flow shear and collisions, to reproduce most of the characteristics
of the observed turbulence. Even so, significant discrepancies remain: an
underprediction by the simulations of the turbulence amplituide and heat flux
at plasma periphery and the finding that the correlation times of the
numerically simulated turbulence are typically two orders of magnitude longer
than those measured in MAST. Comparison of these correlation times with various
linear timescales suggests that, while the measured turbulence is strong and
may be `critically balanced', the simulated turbulence is weak.Comment: 27 pages, 11 figure
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