Edge turbulence measurements in L-mode and I-mode at ASDEX Upgrade

Bielajew, R.; Conway, G. D.; Griener, M.; Happel, T.; Höfler, K.; Howard, N. T.; Hubbard, A. E.; McCarthy, W.; Molina Cabrera, P. A.; Nishizawa, T.; Rodriguez-Fernandez, P.; Silvagni, D.; Vanovac, B.; Wendler, D.; Yoo, C.; White, A. E.

doi:10.1063/5.0088062

Edge turbulence measurements in L-mode and I-mode at ASDEX Upgrade

Journal Article · Mon May 09 00:00:00 EDT 2022 · Physics of Plasmas

DOI:https://doi.org/10.1063/5.0088062· OSTI ID:2567913

; Conway, G. D.; ; ; ; ; Hubbard, A. E.; ; ; ; ; ; ; ; Yoo, C.; White, A. E.

The I-mode confinement regime is promising for future reactor operation due to high energy confinement without high particle confinement. However, the role of edge turbulence in creating I-mode's beneficial transport properties is still unknown. New measurements of edge turbulence (ρpol=0.9−1.0) in L-modes and I-modes at low and high densities at ASDEX Upgrade are presented in this paper. A high radial resolution correlation electron cyclotron emission radiometer measures the broadband turbulence throughout the L-mode and I-mode edge and pedestal. The weakly coherent mode (WCM) is measured in both L-mode and I-mode near the last closed flux surface with Te fluctuation levels of 2.3%–4.2%, with a frequency shift between the two phases related to a deeper Er well in I-mode. An neTe phase diagnostic captures a change of the WCM neTe phase between L-mode and I-mode from −171° to −143°. The thermal He beam diagnostic measures a WCM wavenumber range of −0.5 to −1.0 cm−1. A low-frequency edge oscillation (LFEO) appears in the I-mode phase of these discharges and displays coupling to the WCM, but the LFEO does not appear in the L-mode phase. Linear gyrokinetic simulations of the outer core and pedestal top turbulence indicate that while the dominant turbulent modes in the outer core are ion directed and electrostatic, the turbulence becomes increasingly electron directed and electromagnetic with increasing radius. Collisionality is not found to impact characteristics of the L-mode and I-mode edge turbulence with respect to the presence of the WCM; however, the quality of global confinement decreases with collisionality.

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Research Organization:: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

Sponsoring Organization:: Euratom Research and Training Programme; National Science Foundation (NSF); USDOE; USDOE Office of Science (SC)

Contributing Organization:: ASDEX Upgrade Team; EUROfusion Consortium

Grant/Contract Number:: SC0006419; SC0014264; SC0017381

OSTI ID:: 2567913

Alternate ID(s):: OSTI ID: 1866858
OSTI ID: 1979068

Journal Information:: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 5 Vol. 29; ISSN 1070-664X

Publisher:: American Institute of PhysicsCopyright Statement

Country of Publication:: United States

Language:: English

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