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Title: Grassy-ELM regime with edge resonant magnetic perturbations in fully noninductive plasmas in the DIII-D tokamak

Resonant magnetic perturbations (n=3 RMPs) are used to eliminate large amplitude ELMs and reduce the amplitude of weaker "grassy"-ELMs in DIII-D plasmas relevant to the ITER steady-state mission. Fully non-inductive discharges in the ITER shape and pedestal collisionality (n*e ≈ 0.05-0.15) are routinely achieved in DIII-D with RMP suppression of Type-I ELMs. The residual grassy-ELMs deliver a low peak heat flux to the divertor, within 50% of the inter-ELM heat flux, in plasmas with sustained high H-factor (H98y2≈1.2). These grassy-ELM plasmas have a pedestal width that is typically 10% of the poloidal minor radius and ≈50% wider than EPED model predictions. The operating window for RMP grassy-ELMs in edge magnetic safety factor and external torque is in the range required for a steady-state tokamak reactor, such as q95 between 5.3 and 7.1, and co-Ip neutral beam torque down to 0.7 Nm. Small amplitude RMPs (dBvac/B≈1.5x10-4) are sufficient to access this regime, consistent with the large amplification of the vacuum field by the plasma, typically 3-4x the amplification produced by ITER baseline plasmas due to the high pedestal pressure. Cyclic pulsations are observed in the pedestal and plasma magnetic response, consistent with theoretically predicted limit cycle behavior of magnetic island penetrationmore » and screening. The grassy ELMs are strongly modulated and sometimes fully suppressed during these pedestal pulsations, consistent with the stabilizing effect of resonant field penetration on peeling-ballooning mode stability. The use of low amplitude edge-resonant magnetic perturbations to access enhanced grassy-ELM operation in a naturally wide pedestal plasma with weak confinement degradation opens the possibility for further optimization of the steady-state tokamak by improved coupling between external fields and weakly stable modes of the plasma.« less
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Publication Date:
Grant/Contract Number:
FC02-04ER54698; AC02-09CH11466; AC52-07NA27344; FG02-07ER54917; FG02-04ER54761
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 58; Journal Issue: 10; Journal ID: ISSN 0029-5515
IOP Science
Research Org:
General Atomics, San Diego, CA (United States); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Oak Ridge Inst. for Science and Education (ORISE), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Nuclear Energy (NE); USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
Country of Publication:
United States
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; 43 PARTICLE ACCELERATORS; Resonant-magnetic-perturbations; edge-localized-modes; pedestal stability
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1462193