L – H transition trigger physics in ITER-similar plasmas with applied n = 3 magnetic perturbations
Abstract
The L–H transition power threshold P LH is observed to increase with applied n = 3 resonant magnetic perturbations (RMP) in ITER-similar-shape plasmas with balanced neutral beam torque injection in DIII-D. The increase is most pronounced with added electron–cyclotron heating: P LH increases with decreasing edge plasma collisionality as P LH/P LH-08 ~ (ν *)-0.5, where P LH-08 is the 2008 ITPA multi-machine power threshold scaling. This result raises concerns for H-mode access at low edge collisionality in ITER, where RMP may have to be applied before the L–H transition to safely suppress the first edge-localized mode. Non-axisymmetric modifications with RMP include a simultaneous reduction of the radial electric field (E r) well depth and E× B shear. This can be attributed to increasing edge toroidal co-current rotation, and is consistent with substantially increased local long-wavelength turbulence (measured via beam emission spectroscopy). At high RMP perturbation strength the edge electric field E r reverses sign locally (becomes positive), with changes in dominant turbulence modes. Edge magnetic stochasticity provides an attractive explanation of the observed modifications, and the observed changes in toroidal rotation and E r are consistent with a simple fluid model describing radial electron current flow along stochastic fieldlines.more »
- Authors:
-
- Univ. of California, Los Angeles, CA (United States)
- Univ. of Wisconsin, Madison, WI (United States)
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- General Atomics, San Diego, CA (United States)
- Univ. of California San Diego, La Jolla, CA (United States)
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
- Publication Date:
- Research Org.:
- General Atomics, San Diego, CA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Org.:
- USDOE Office of Science (SC), Fusion Energy Sciences (FES)
- OSTI Identifier:
- 1569024
- Alternate Identifier(s):
- OSTI ID: 1761760
- Grant/Contract Number:
- FC02-04ER54698; FG02-08ER54984; FG02-89ER53296; FG02-08ER54999; AC05-00OR22725
- Resource Type:
- Accepted Manuscript
- Journal Name:
- Nuclear Fusion
- Additional Journal Information:
- Journal Volume: 59; Journal Issue: 12; Journal ID: ISSN 0029-5515
- Publisher:
- IOP Science
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; L-H transition; Resonant magnetic perturbations; Turbulence
Citation Formats
Schmitz, L., Kriete, D. M., Wilcox, R. S., Rhodes, T. L., Zeng, L., Yan, Z., McKee, G. R., Evans, T. E., Paz-Soldan, C., Gohil, P., Lyons, B., Petty, C. C., Orlov, D., and Marinoni, A. L – H transition trigger physics in ITER-similar plasmas with applied n = 3 magnetic perturbations. United States: N. p., 2019.
Web. doi:10.1088/1741-4326/ab36bf.
Schmitz, L., Kriete, D. M., Wilcox, R. S., Rhodes, T. L., Zeng, L., Yan, Z., McKee, G. R., Evans, T. E., Paz-Soldan, C., Gohil, P., Lyons, B., Petty, C. C., Orlov, D., & Marinoni, A. L – H transition trigger physics in ITER-similar plasmas with applied n = 3 magnetic perturbations. United States. https://doi.org/10.1088/1741-4326/ab36bf
Schmitz, L., Kriete, D. M., Wilcox, R. S., Rhodes, T. L., Zeng, L., Yan, Z., McKee, G. R., Evans, T. E., Paz-Soldan, C., Gohil, P., Lyons, B., Petty, C. C., Orlov, D., and Marinoni, A. Tue .
"L – H transition trigger physics in ITER-similar plasmas with applied n = 3 magnetic perturbations". United States. https://doi.org/10.1088/1741-4326/ab36bf. https://www.osti.gov/servlets/purl/1569024.
@article{osti_1569024,
title = {L – H transition trigger physics in ITER-similar plasmas with applied n = 3 magnetic perturbations},
author = {Schmitz, L. and Kriete, D. M. and Wilcox, R. S. and Rhodes, T. L. and Zeng, L. and Yan, Z. and McKee, G. R. and Evans, T. E. and Paz-Soldan, C. and Gohil, P. and Lyons, B. and Petty, C. C. and Orlov, D. and Marinoni, A.},
abstractNote = {The L–H transition power threshold P LH is observed to increase with applied n = 3 resonant magnetic perturbations (RMP) in ITER-similar-shape plasmas with balanced neutral beam torque injection in DIII-D. The increase is most pronounced with added electron–cyclotron heating: P LH increases with decreasing edge plasma collisionality as P LH/P LH-08 ~ (ν *)-0.5, where P LH-08 is the 2008 ITPA multi-machine power threshold scaling. This result raises concerns for H-mode access at low edge collisionality in ITER, where RMP may have to be applied before the L–H transition to safely suppress the first edge-localized mode. Non-axisymmetric modifications with RMP include a simultaneous reduction of the radial electric field (E r) well depth and E× B shear. This can be attributed to increasing edge toroidal co-current rotation, and is consistent with substantially increased local long-wavelength turbulence (measured via beam emission spectroscopy). At high RMP perturbation strength the edge electric field E r reverses sign locally (becomes positive), with changes in dominant turbulence modes. Edge magnetic stochasticity provides an attractive explanation of the observed modifications, and the observed changes in toroidal rotation and E r are consistent with a simple fluid model describing radial electron current flow along stochastic fieldlines. The observed collisionality dependence of the L-mode edge electric field with applied RMP is also qualitatively consistent with this model. Reflectometry data indicate a significant reduction of the normalized L-mode radial density gradient a/L n at high RMP field with simultaneous increase in radial particle flux and electron thermal flux from power balance analysis. We conjecture that the increase of P LH with RMP results from the combined effects of reduced E× B flow shear (increasing turbulent transport levels) and toroidal/poloidal flow modulation due to edge stochasticity. Initial experiments indicate that non-resonant n = 3 magnetic perturbations lead only to relatively small changes in E r, E × B shear and fluctuation characteristics, and have less impact on the L–H transition power threshold. This motivates further exploration of the RMP spectrum dependence of P LH for possible mitigation of the observed threshold increase.},
doi = {10.1088/1741-4326/ab36bf},
journal = {Nuclear Fusion},
number = 12,
volume = 59,
place = {United States},
year = {2019},
month = {9}
}
Web of Science
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