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Title: Suppression of Large Edge Localized Modes with a Stochastic Magnetic Boundary in High Confinement DIII-D Plasmas

Suppression of Large Edge Localized Modes with a Stochastic Magnetic Boundary in High Confinement DIII-D Plasmas Large sub-millisecond heat pulses due to Type-I ELMs have been reproducibly eliminated in DIII-D for periods approaching 7 energy confinement times with small dc currents driven in a simple magnetic perturbation coil. The current required to eliminate all but a few isolated Type-I ELM impulses during a perturbation coil pulse lasting several seconds is less than 0.4% of plasma current. Based on vacuum magnetic field line modeling, perturbation fields from the coil resonate strongly with plasma flux surfaces across most of the pedestal region (0.9 {le} {psi}{sub N} {le} 1.0) when q95 = 3.7{plus_minus}0.2 creating small remnant magnetic islands surrounded by weakly stochastic field lines. Under the best ELM suppression conditions, the stored energy, {beta}N and H-mode quality factor are unaffected by the perturbation field along with the electron pressure profile, radial electric field and poloidal rotation across the pedestal. Consequently, the H-mode transport barrier and global energy confinement time is also unaltered in these cases. Although some isolated ELM-like events typically occur during the perturbation coil pulse, long periods free of large Type-I ELMs ({Delta}t > 4-6 {tau}{sub E}) have been reproduced numerous times, on multiple experimental run days. Several Type-I ELM suppression and modification behaviors have been identified more » and studied over a range of discharge conditions including those matching the ITER scenario 2 flux surface shape and aspect ratio scaled down by a factor of 3.5 to fit in the DIII-D vacuum vessel. Since large Type-I ELM impulses represent a severe constraint on the survivability of the divertor target plates in future fusion devices such as ITER, a proven method of eliminating these impulses is critical for the development of tokamak reactors. Results presented in this paper suggest that non-axisymmetric edge magnetic perturbations could be a promising option for controlling ELMs in future tokamaks such as ITER. « less
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Publication Date:
OSTI Identifier:15014746
Report Number(s):UCRL-CONF-207379
TRN: US0800913
DOE Contract Number:W-7405-ENG-48
Resource Type:Conference
Resource Relation:Conference: Presented at: 20th IAEA Conference, Vilamoura, Portugal, Nov 01 - Nov 06, 2004
Research Org:Lawrence Livermore National Laboratory (LLNL), Livermore, CA
Sponsoring Org:USDOE
Country of Publication:United States
Language:English
Subject: 70 PLASMA PHYSICS AND FUSION; ASPECT RATIO; CONFINEMENT; CONFINEMENT TIME; DOUBLET-3 DEVICE; EDGE LOCALIZED MODES; ELECTRIC CURRENTS; ELECTRIC FIELDS; IAEA; MAGNETIC FIELDS; MAGNETIC ISLANDS; MAGNETIC SURFACES; QUALITY FACTOR; STORED ENERGY