51st Annual Meeting of the APS Division of Plasma Physics
Volume 54, Number 15
Monday–Friday, November 2–6, 2009;
Atlanta, Georgia
Session PI2: Tokamak Physics: Edge, Scrape-off Layer and Wall
2:00 PM–5:00 PM,
Wednesday, November 4, 2009
Room: Centennial I
Chair: Andrea Garofalo, General Atomics
Abstract ID: BAPS.2009.DPP.PI2.3
Abstract: PI2.00003 : Modification of Edge Profiles and Stability with Lithium Wall Coatings in NSTX*
3:00 PM–3:30 PM
Preview Abstract
Abstract
Author:
Rajesh Maingi
(Oak Ridge National Laboratory)
Rapidly growing instabilities known as Edge Localized Modes
(ELMs) are commonly observed in high-confinement (H-mode) regimes
in many toroidal confinement devices. The reduction or
elimination of ELMs with high confinement is essential for ITER,
which has been designed for H-mode operation. Large ELMs are
thought to be triggered by exceeding either edge current density
limits (peeling modes) and/or edge pressure gradient limits
(ballooning modes) [1]. Edge stability calculations have
indicated that spherical tori should have access to higher
pressure gradients and H-mode pedestal heights than higher aspect
ratio tokamaks, owing to high magnetic shear and possible access
to second stability regimes [2]. Such a regime was
recently discovered in the National Spherical Torus Experiment
(NSTX) following the application of Lithium onto the graphite
plasma facing components [3]. ELMs were eliminated in phases [4],
with the resulting pressure gradients and pedestal widths
increasing substantially [5]. The modification of the pressure
profile originated mainly from reduced recycling and edge
fueling, which relaxed the edge density gradients. PEST
and ELITE calculations have confirmed that the resulting pressure
profiles were further from the stability boundary than reference
discharges. The resulting discharges are ELM-free with a 50{\%}
increase in normalized energy confinement, up to the global
$\beta _{N} \sim$ 5.5-6 limit. While the ELM-free
discharges ultimately suffer radiative collapse, pulsed
3-d magnetic fields are used to trigger ELMs and purge impurities
[6].
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[1] P. B. Snyder, et. al., \textit{Physics of Plasmas} \textbf{9}
(2002) 2037.
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[2] P. B. Snyder, \textit{Plasma Physics Controlled Fusion}
\textbf{46} (2004) A131.
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[3] H. W. Kugel, et. al., \textit{Physics of Plasmas} \textbf{15}
(2008) 056118.
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[4] D. M. Mansfield, et. al., \textit{J. Nucl. Materials}
\textbf{390-391} (2009) 764
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[5] R. Maingi et. al., \textit{Physical Review Letters} (2009) at
press.
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[6] J.M. Canik, et. al, \textit{Nucl. Fusion} (2009) submitted.
*Supported in part by contracts DE-AC05-00OR22725 and DE-AC02-09CH11466.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2009.DPP.PI2.3