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Title: L-H transition trigger physics in ITER-similar plasmas with applied n = 3 magnetic perturbations

Abstract

The L–H transition power threshold PLH 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: PLH increases with decreasing edge plasma collisionality as PLH/PLH-08 ~ (ν*)−0.5, where PLH-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 (Er) 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 Er 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 Er 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 appliedmore » RMP is also qualitatively consistent with this model. Reflectometry data indicate a significant reduction of the normalized L-mode radial density gradient a/Ln 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 PLH 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 Er, 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 PLH for possible mitigation of the observed threshold increase.« less

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
DOE Contract Number:  
FC02-04ER54698; AC05-00OR22725; FG02-08ER54999; FG02-89ER53296; FG02-08ER54984
Research Org.:
General Atomics, San Diego, CA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Wisconsin, Madison, WI (United States); Univ. of California, Los Angeles, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
OSTI Identifier:
1881852
DOI:
https://doi.org/10.7910/DVN/JI20PQ

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., 2021. Web. doi:10.7910/DVN/JI20PQ.
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. doi:https://doi.org/10.7910/DVN/JI20PQ
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. 2021. "L-H transition trigger physics in ITER-similar plasmas with applied n = 3 magnetic perturbations". United States. doi:https://doi.org/10.7910/DVN/JI20PQ. https://www.osti.gov/servlets/purl/1881852. Pub date:Tue Mar 30 00:00:00 EDT 2021
@article{osti_1881852,
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 PLH 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: PLH increases with decreasing edge plasma collisionality as PLH/PLH-08 ~ (ν*)−0.5, where PLH-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 (Er) 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 Er 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 Er 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/Ln 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 PLH 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 Er, 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 PLH for possible mitigation of the observed threshold increase.},
doi = {10.7910/DVN/JI20PQ},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2021},
month = {3}
}

Works referencing / citing this record:

LH transition trigger physics in ITER-similar plasmas with applied n   =  3 magnetic perturbations
journal, September 2019