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Title: ELM suppression in helium plasmas with 3D magnetic fields

Abstract

Experiments in DIII-D, using non-axisymmetric magnetic perturbation fields in high-purity low toroidal rotation, 4He plasmas have resulted in Type-I edge localized mode (ELM) suppression and mitigation. Suppression is obtained in plasmas with zero net input torque near the L–H power threshold using either electron cyclotron resonant heating (ECRH) or balanced co- and counter-I p neutral beam injection (NBI) resulting in conditions equivalent to those expected in ITER's non-active operating phase. In low-power ECRH H-modes, periods with uncontrolled density and impurity radiation excursions are prevented by applying n = 3 non-axisymmetric magnetic perturbation fields. ELM suppression results from a reduction and an outward shift of the electron pressure gradient peak compared to that in the high-power ELMing phase. Here, the change in the electron pressure gradient peak is primarily due to a drop in the pedestal temperature rather than the pedestal density.

Authors:
 [1];  [2];  [3];  [4];  [5];  [6];  [4];  [1];  [1];  [3];  [4];  [1];  [7]
  1. General Atomics, San Diego, CA (United States)
  2. ITER Organization, St. Paul lez Durance (France)
  3. Univ. of California San Diego, La Jolla, CA (United States)
  4. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  5. Ludwig Maximilian Univ., Munich (Germany)
  6. General Atomics, San Diego, CA (United States); Oak Ridge Institute for Science Education, Oak Ridge, TN (United States)
  7. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1373695
Alternate Identifier(s):
OSTI ID: 1374585
Grant/Contract Number:
FC02-04ER54698
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 57; Journal Issue: 8; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ELM suppression; Helium plasmas; resonant magnetic perturbations; DIII-D; ITER

Citation Formats

Evans, T. E., Loarte, A., Orlov, D. M., Grierson, B. A., Knolker, M. M., Lyons, B. C., Cui, L., Gohil, P., Groebner, R. J., Moyer, R. A., Nazikian, R., Osborne, T. H., and Unterberg, E. A. ELM suppression in helium plasmas with 3D magnetic fields. United States: N. p., 2017. Web. doi:10.1088/1741-4326/aa7530.
Evans, T. E., Loarte, A., Orlov, D. M., Grierson, B. A., Knolker, M. M., Lyons, B. C., Cui, L., Gohil, P., Groebner, R. J., Moyer, R. A., Nazikian, R., Osborne, T. H., & Unterberg, E. A. ELM suppression in helium plasmas with 3D magnetic fields. United States. doi:10.1088/1741-4326/aa7530.
Evans, T. E., Loarte, A., Orlov, D. M., Grierson, B. A., Knolker, M. M., Lyons, B. C., Cui, L., Gohil, P., Groebner, R. J., Moyer, R. A., Nazikian, R., Osborne, T. H., and Unterberg, E. A. Wed . "ELM suppression in helium plasmas with 3D magnetic fields". United States. doi:10.1088/1741-4326/aa7530.
@article{osti_1373695,
title = {ELM suppression in helium plasmas with 3D magnetic fields},
author = {Evans, T. E. and Loarte, A. and Orlov, D. M. and Grierson, B. A. and Knolker, M. M. and Lyons, B. C. and Cui, L. and Gohil, P. and Groebner, R. J. and Moyer, R. A. and Nazikian, R. and Osborne, T. H. and Unterberg, E. A.},
abstractNote = {Experiments in DIII-D, using non-axisymmetric magnetic perturbation fields in high-purity low toroidal rotation, 4He plasmas have resulted in Type-I edge localized mode (ELM) suppression and mitigation. Suppression is obtained in plasmas with zero net input torque near the L–H power threshold using either electron cyclotron resonant heating (ECRH) or balanced co- and counter-I p neutral beam injection (NBI) resulting in conditions equivalent to those expected in ITER's non-active operating phase. In low-power ECRH H-modes, periods with uncontrolled density and impurity radiation excursions are prevented by applying n = 3 non-axisymmetric magnetic perturbation fields. ELM suppression results from a reduction and an outward shift of the electron pressure gradient peak compared to that in the high-power ELMing phase. Here, the change in the electron pressure gradient peak is primarily due to a drop in the pedestal temperature rather than the pedestal density.},
doi = {10.1088/1741-4326/aa7530},
journal = {Nuclear Fusion},
number = 8,
volume = 57,
place = {United States},
year = {Wed Jun 21 00:00:00 EDT 2017},
month = {Wed Jun 21 00:00:00 EDT 2017}
}

Journal Article:
Free Publicly Available Full Text
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  • Experiments in DIII-D, using non-axisymmetric magnetic perturbation fields in high-purity low toroidal rotation, 4He plasmas have resulted in Type-I Edge Localized Mode (ELM) suppression and mitigation. Suppression is obtained in plasmas with zero net input torque near the L-H power threshold using either Electron Cyclotron Resonant Heating (ECRH) or balanced co- and counter-Ip Neutral Beam Injection (NBI) resulting in conditions equivalent to those expected in ITER’s non-active operating phase. In low-power ECRH Hmodes, periods with uncontrolled density and impurity radiation excursions are prevented by applying n=3 non-axisymmetric magnetic perturbation fields. ELM suppression results from a reduction and an outward shiftmore » of the electron pressure gradient peak compared to that in the high-power ELMing phase. The change in the electron pressure gradient peak is primarily due to a drop in the pedestal temperature rather than the pedestal density.« less
    Cited by 1
  • Here, experiments have been executed in the DIII-D tokamak to extend suppression of Edge Localized Modes (ELMs) with Resonant Magnetic Perturbations (RMPs) to ITER-relevant levels of beam torque. The results support the hypothesis for RMP ELM suppression based on transition from an ideal screened response to a tearing response at a resonant surface that prevents expansion of the pedestal to an unstable width.
  • Some recent experimental observations have found turbulent fluctuation structures that are non-axisymmetric in a tokamak with applied 3D fields. Here, two fluid resistive effects are shown to produce changes relevant to turbulent transport in the modeled 3D magnetohydrodynamic (MHD) equilibrium of tokamak pedestals with these 3D fields applied. Ideal MHD models are insufficient to reproduce the relevant effects. By calculating the ideal 3D equilibrium using the VMEC code, the geometric shaping parameters that determine linear turbulence stability, including the normal curvature and local magnetic shear, are shown to be only weakly modified by applied 3D fields in the DIII-D tokamak.more » These ideal MHD effects are therefore not sufficient to explain the observed changes to fluctuations and transport. Using the M3D-C1 code to model the 3D equilibrium, density is shown to be redistributed on flux surfaces in the pedestal when resistive two fluid effects are included, while islands are screened by rotation in this region. Furthermore, the redistribution of density results in density and pressure gradient scale lengths that vary within pedestal flux surfaces between different helically localized flux tubes. This would produce different drive terms for trapped electron mode and kinetic ballooning mode turbulence, the latter of which is expected to be the limiting factor for pedestal pressure gradients in DIII-D.« less
  • Some recent experimental observations have found turbulent fluctuation structures that are non-axisymmetric in a tokamak with applied 3D fields. Here, two fluid resistive effects are shown to produce changes relevant to turbulent transport in the modeled 3D magnetohydrodynamic (MHD) equilibrium of tokamak pedestals with these 3D fields applied. Ideal MHD models are insufficient to reproduce the relevant effects. By calculating the ideal 3D equilibrium using the VMEC code, the geometric shaping parameters that determine linear turbulence stability, including the normal curvature and local magnetic shear, are shown to be only weakly modified by applied 3D fields in the DIII-D tokamak.more » These ideal MHD effects are therefore not sufficient to explain the observed changes to fluctuations and transport. Using the M3D-C1 code to model the 3D equilibrium, density is shown to be redistributed on flux surfaces in the pedestal when resistive two fluid effects are included, while islands are screened by rotation in this region. Furthermore, the redistribution of density results in density and pressure gradient scale lengths that vary within pedestal flux surfaces between different helically localized flux tubes. This would produce different drive terms for trapped electron mode and kinetic ballooning mode turbulence, the latter of which is expected to be the limiting factor for pedestal pressure gradients in DIII-D.« less