The relationships between edge localized modes suppression, pedestal profiles and lithium wall coatings in NSTX

Journal Article · Sat Jan 01 04:00:00 EST 2011 · Plasma Physics and Controlled Fusion

DOI:https://doi.org/10.1088/0741-3335/53/10/105011· OSTI ID:1037129

Boyle, D P ^[1]; Maingi, R ^[2]; Snyder, P B ^[3]; Manickam, J ^[4]; Osborne, T H ^[3]; Bell, R E ^[4]; LeBlanc, B P ^[4]

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1. Princeton University
2. Oak Ridge National Laboratory (ORNL)
3. General Atomics, San Diego
4. Princeton Plasma Physics Laboratory (PPPL)

Recently in the National Spherical Torus Experiment (NSTX), increasing lithium wall coatings suppressed edge localized modes (ELMs), gradually but not quite monotonically. This work details profile and stability analysis as ELMs disappeared throughout the lithium scan. While the quantity of lithium deposited between discharges did not uniquely determine the presence of ELMs, profile analysis demonstrated that lithium was correlated with wider density and pressure pedestals with peak gradients farther from the separatrix. Moreover, the ELMy and ELM-free discharges were cleanly separated by their density and pedestal widths and peak gradient locations. Ultimately, ELMs were only suppressed when lithium caused the density pedestal to widen and shift inward. These changes in the density gradient were directly reflected in the pressure gradient and calculated bootstrap current. This supports the theory that ELMs in NSTX are caused by peeling and/or ballooning modes, as kink/peeling modes are stabilized when the edge current and pressure gradient shift away from the separatrix. Edge stability analysis using ELITE corroborated this picture, as reconstructed equilibria from ELM-free discharges were generally farther from their kink/peeling stability boundaries than ELMy discharges. We conclude that density profile control provided by lithium is the key first step to ELM suppression in NSTX.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1037129
• Journal Information: Plasma Physics and Controlled Fusion, Journal Name: Plasma Physics and Controlled Fusion Journal Issue: 10 Vol. 53; ISSN 0741-3335
• Country of Publication: United States
• Language: English

Related Subjects

BALLOONING MODES
DENSITY
DIII-D
ITER
PERFORMANCE
PHYSICS
PLASMAS
REGIME
STABILITY
TOKAMAKS