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

Abstract

Here, resonant magnetic perturbations (n=3 RMPs) are used to suppress large amplitude ELMs and mitigate naturally occurring "grassy"-ELMs in DIII-D plasmas relevant to the ITER steady-state mission. Fully non-inductive discharges in the ITER shape and pedestal collisionality (ν$$*\atop{e}$$ ≈ 0.05-0.15) are routinely achieved in DIII-D with RMP suppression of the Type-I ELMs. The residual grassy-ELMs deliver a low peak heat flux to the divertor as low as 1.2x the inter-ELM heat flux in plasmas with sustained high H-factor (H 98y2 ≈ 1.2). The operating window for the RMP grassy-ELM regime is q 95 = 5.3-7.1 and external torque in the range 9 - 0.7 Nm in the co-Ip direction, which is in the range required for a steady-state tokamak reactor. The RMP grassy-ELM regime is associated with a two-step pedestal, with strong flattening of the density around the zero crossing in the E x B shear. The edge magnetic response of the plasma to the n = 3 RMP is found to be ≈2-3x larger than for comparable ITER baseline plasmas (β N ≈ 1.8, q 95 ≈ 3.1). The amplification of the RMP is consistent with the weak magnetic perturbation level (δB/B ≈ 1x10 -4) required for effectively Type-I ELM suppression. Cyclic variations in the pedestal pressure, width, and toroidal rotation are observed in these plasmas, correlated with cyclic variations in the strength and frequency of the grassy- ELMs. Extended MHD analysis and magnetic measurements indicate that these pedestal pulsations are driven by cyclic variations in the resonant field strength at the top of the pedestal. These pedestal pulsations reveal that the grassy-ELMs are correlated with the proximity of the pedestal to the low-n PBMs (Peeling-Ballooning Modes) stability boundary. The use of low amplitude magnetic fields to access grassy-ELM conditions free of Type-I ELMs in high beta poloidal plasmas (β P ≈ 1.5-2.0) opens the possibility for the further optimization of the steady-state tokamak by use of edge resonant magnetic perturbations.

Authors:
ORCiD logo [1];  [2]; ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [2]; ORCiD logo [2]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [3];  [4]; ORCiD logo [1];  [5]; ORCiD logo [5];  [2]; ORCiD logo [2];  [6];  [7]; ORCiD logo [2]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  2. General Atomics, San Diego, CA (United States)
  3. Ludwig Maximilian Univ., Munich (Germany)
  4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  5. Univ. of California, San Diego, CA (United States)
  6. Columbia Univ., New York, NY (United States)
  7. Oak Ridge Inst. for Science and Education (ORISE), Oak Ridge, TN (United States)
Publication Date:
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)
OSTI Identifier:
1462205
Alternate Identifier(s):
OSTI ID: 1462193
Grant/Contract Number:  
FC02-04ER54698; AC02-09CH11466; AC52-07NA27344; FG02-07ER54917; FG02-04ER54761
Resource Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 58; Journal Issue: 10; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; 43 PARTICLE ACCELERATORS; Resonant-magnetic-perturbations; edge-localized-modes; pedestal stability

Citation Formats

Nazikian, R., Petty, C. C., Bortolon, A., Chen, Xi, Eldon, D., Evans, T. E., Grierson, B. A., Ferraro, N. M., Haskey, S. R., Knolker, M., Lasnier, C., Logan, N. C., Moyer, R. A., Orlov, D., Osborne, T. H., Paz-Soldan, C., Turco, F., Wang, H. Q., and Weisberg, D. B. Grassy-ELM regime with edge resonant magnetic perturbations in fully noninductive plasmas in the DIII-D tokamak. United States: N. p., 2018. Web. doi:10.1088/1741-4326/aad20d.
Nazikian, R., Petty, C. C., Bortolon, A., Chen, Xi, Eldon, D., Evans, T. E., Grierson, B. A., Ferraro, N. M., Haskey, S. R., Knolker, M., Lasnier, C., Logan, N. C., Moyer, R. A., Orlov, D., Osborne, T. H., Paz-Soldan, C., Turco, F., Wang, H. Q., & Weisberg, D. B. Grassy-ELM regime with edge resonant magnetic perturbations in fully noninductive plasmas in the DIII-D tokamak. United States. doi:10.1088/1741-4326/aad20d.
Nazikian, R., Petty, C. C., Bortolon, A., Chen, Xi, Eldon, D., Evans, T. E., Grierson, B. A., Ferraro, N. M., Haskey, S. R., Knolker, M., Lasnier, C., Logan, N. C., Moyer, R. A., Orlov, D., Osborne, T. H., Paz-Soldan, C., Turco, F., Wang, H. Q., and Weisberg, D. B. Fri . "Grassy-ELM regime with edge resonant magnetic perturbations in fully noninductive plasmas in the DIII-D tokamak". United States. doi:10.1088/1741-4326/aad20d. https://www.osti.gov/servlets/purl/1462205.
@article{osti_1462205,
title = {Grassy-ELM regime with edge resonant magnetic perturbations in fully noninductive plasmas in the DIII-D tokamak},
author = {Nazikian, R. and Petty, C. C. and Bortolon, A. and Chen, Xi and Eldon, D. and Evans, T. E. and Grierson, B. A. and Ferraro, N. M. and Haskey, S. R. and Knolker, M. and Lasnier, C. and Logan, N. C. and Moyer, R. A. and Orlov, D. and Osborne, T. H. and Paz-Soldan, C. and Turco, F. and Wang, H. Q. and Weisberg, D. B.},
abstractNote = {Here, resonant magnetic perturbations (n=3 RMPs) are used to suppress large amplitude ELMs and mitigate naturally occurring "grassy"-ELMs in DIII-D plasmas relevant to the ITER steady-state mission. Fully non-inductive discharges in the ITER shape and pedestal collisionality (ν$*\atop{e}$ ≈ 0.05-0.15) are routinely achieved in DIII-D with RMP suppression of the Type-I ELMs. The residual grassy-ELMs deliver a low peak heat flux to the divertor as low as 1.2x the inter-ELM heat flux in plasmas with sustained high H-factor (H98y2 ≈ 1.2). The operating window for the RMP grassy-ELM regime is q95 = 5.3-7.1 and external torque in the range 9 - 0.7 Nm in the co-Ip direction, which is in the range required for a steady-state tokamak reactor. The RMP grassy-ELM regime is associated with a two-step pedestal, with strong flattening of the density around the zero crossing in the E x B shear. The edge magnetic response of the plasma to the n = 3 RMP is found to be ≈2-3x larger than for comparable ITER baseline plasmas (βN ≈ 1.8, q95 ≈ 3.1). The amplification of the RMP is consistent with the weak magnetic perturbation level (δB/B ≈ 1x10-4) required for effectively Type-I ELM suppression. Cyclic variations in the pedestal pressure, width, and toroidal rotation are observed in these plasmas, correlated with cyclic variations in the strength and frequency of the grassy- ELMs. Extended MHD analysis and magnetic measurements indicate that these pedestal pulsations are driven by cyclic variations in the resonant field strength at the top of the pedestal. These pedestal pulsations reveal that the grassy-ELMs are correlated with the proximity of the pedestal to the low-n PBMs (Peeling-Ballooning Modes) stability boundary. The use of low amplitude magnetic fields to access grassy-ELM conditions free of Type-I ELMs in high beta poloidal plasmas (βP ≈ 1.5-2.0) opens the possibility for the further optimization of the steady-state tokamak by use of edge resonant magnetic perturbations.},
doi = {10.1088/1741-4326/aad20d},
journal = {Nuclear Fusion},
number = 10,
volume = 58,
place = {United States},
year = {2018},
month = {7}
}

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    Works referencing / citing this record:

    Optimizing multi-modal, non-axisymmetric plasma response metrics with additional coil rows on DIII-D
    journal, July 2019