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Title: Long-lived predator-prey dynamics in the pedestal of near-zero torque high performance DIII-D plasmas

Abstract

Quiescent high performance plasmas (often termed QH-mode) are attractive due to the replacement of potentially damaging energy and particle releases known as edge localized modes (ELMs) by relatively benign edge harmonic oscillations (EHO). These EHOs are believed to be driven unstable by edge current and/or edge toroidal rotational shear and contribute to edge particle transport. Decreasing the applied neutral beam torque in standard QH- mode discharge leads to an improved quiescent phase of higher and wider pedestal, also known as the wide-pedestal QH-mode. This work expands upon the observed limit cycle oscillation (LCO) dynamics in this wide pedestal QH-mode. The onset of these LCOs after wide-pedestal transition are found to be correlated with the disappearance of coherent EHOs which happens either when the edge maximum bootstrap current decreases after the transition or when the toroidal rotation is decreased consistent with simulation predictions. Sustainment of this quasi-stationary oscillating regime is found to be possible due to a predator-prey type competition between E×B velocity shear and turbulence density fluctuations facilitated by an inward propagation of non-zonal flow like toroidally and poloidally symmetric E×B velocity perturbations from these LCOs. Furthermore, these LCO dynamics are further controlled by adding electron cyclotron heating (ECH) tomore » a neutral beam heated wide-pedestal QH-mode discharge which led to surprising increase in energy confinement correlated with a concomitant decrease in edge turbulence in contrast to normally observed confinement degradation in H-mode with ECH.« less

Authors:
ORCiD logo [1];  [1]; ORCiD logo [2]; ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3];  [2]; ORCiD logo [2];  [1]
  1. Univ. of California, Los Angeles, CA (United States)
  2. General Atomics, San Diego, CA (United States)
  3. Univ. of Texas, Austin, TX (United States)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
OSTI Identifier:
1560136
Alternate Identifier(s):
OSTI ID: 1560341
Report Number(s):
DOE-GA-54698
Journal ID: ISSN 1070-664X; TRN: US2000462
Grant/Contract Number:  
FC02-04ER54698; FG02-08ER54984
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 26; Journal Issue: 9; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Barada, K., Rhodes, T. L., Burrell, K. H., Zeng, L., Chen, Xi, Austin, M. E., Bardóczi, L., Muscatello, C. M., and Peebles, W. A. Long-lived predator-prey dynamics in the pedestal of near-zero torque high performance DIII-D plasmas. United States: N. p., 2019. Web. doi:10.1063/1.5097143.
Barada, K., Rhodes, T. L., Burrell, K. H., Zeng, L., Chen, Xi, Austin, M. E., Bardóczi, L., Muscatello, C. M., & Peebles, W. A. Long-lived predator-prey dynamics in the pedestal of near-zero torque high performance DIII-D plasmas. United States. doi:10.1063/1.5097143.
Barada, K., Rhodes, T. L., Burrell, K. H., Zeng, L., Chen, Xi, Austin, M. E., Bardóczi, L., Muscatello, C. M., and Peebles, W. A. Thu . "Long-lived predator-prey dynamics in the pedestal of near-zero torque high performance DIII-D plasmas". United States. doi:10.1063/1.5097143. https://www.osti.gov/servlets/purl/1560136.
@article{osti_1560136,
title = {Long-lived predator-prey dynamics in the pedestal of near-zero torque high performance DIII-D plasmas},
author = {Barada, K. and Rhodes, T. L. and Burrell, K. H. and Zeng, L. and Chen, Xi and Austin, M. E. and Bardóczi, L. and Muscatello, C. M. and Peebles, W. A.},
abstractNote = {Quiescent high performance plasmas (often termed QH-mode) are attractive due to the replacement of potentially damaging energy and particle releases known as edge localized modes (ELMs) by relatively benign edge harmonic oscillations (EHO). These EHOs are believed to be driven unstable by edge current and/or edge toroidal rotational shear and contribute to edge particle transport. Decreasing the applied neutral beam torque in standard QH- mode discharge leads to an improved quiescent phase of higher and wider pedestal, also known as the wide-pedestal QH-mode. This work expands upon the observed limit cycle oscillation (LCO) dynamics in this wide pedestal QH-mode. The onset of these LCOs after wide-pedestal transition are found to be correlated with the disappearance of coherent EHOs which happens either when the edge maximum bootstrap current decreases after the transition or when the toroidal rotation is decreased consistent with simulation predictions. Sustainment of this quasi-stationary oscillating regime is found to be possible due to a predator-prey type competition between E×B velocity shear and turbulence density fluctuations facilitated by an inward propagation of non-zonal flow like toroidally and poloidally symmetric E×B velocity perturbations from these LCOs. Furthermore, these LCO dynamics are further controlled by adding electron cyclotron heating (ECH) to a neutral beam heated wide-pedestal QH-mode discharge which led to surprising increase in energy confinement correlated with a concomitant decrease in edge turbulence in contrast to normally observed confinement degradation in H-mode with ECH.},
doi = {10.1063/1.5097143},
journal = {Physics of Plasmas},
number = 9,
volume = 26,
place = {United States},
year = {2019},
month = {9}
}

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