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

Barada, K.; Rhodes, T. L.; Burrell, K. H.; Zeng, L.; Chen, Xi; Austin, M. E.; Bardóczi, L.; Muscatello, C. M.; Peebles, W. A.

doi:10.1063/1.5097143

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

Journal Article · Thu Sep 05 00:00:00 EDT 2019 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.5097143· OSTI ID:1560136

^[1]; Rhodes, T. L. ^[1];

^[2];

^[1];

^[2];

^[3]; Bardóczi, L. ^[2];

^[2]; Peebles, W. A. ^[1]

Univ. of California, Los Angeles, CA (United States)
General Atomics, San Diego, CA (United States)
Univ. of Texas, Austin, TX (United States)

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 by relatively benign edge harmonic oscillations (EHOs). 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 [Burrell et al., Phys. Plasmas 23, 056103 (2016)]. This work expands upon the observed limit cycle oscillation (LCO) dynamics [Barada et al., Phys. Rev. Lett. 120, 135002 (2018)] in this wide pedestal QH-mode. The onset of these LCOs after wide-pedestal transition is 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 quasistationary 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 nonzonal flow like toroidally and poloidally symmetric E × B velocity perturbations from these LCOs. 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 a 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.

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Research Organization:: General Atomics, San Diego, CA (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Fusion Energy Sciences (FES)

Grant/Contract Number:: FC02-04ER54698; FG02-08ER54984

OSTI ID:: 1560136

Alternate ID(s):: OSTI ID: 1560341

Report Number(s):: DOE-GA-54698; TRN: US2000462

Journal Information:: Physics of Plasmas, Vol. 26, Issue 9; ISSN 1070-664X

Publisher:: American Institute of Physics (AIP)Copyright Statement

Country of Publication:: United States

Language:: English

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Cited by: 5 works

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