April 4-6

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Author: Stefan P Tirkas
Requested Type: Poster
Submitted: 2022-03-03 15:18:51

Co-authors: Haotian Chen, Gabriele Merlo, Scott Parker

Contact Info:
University of Colorado, Boulder
4500 Baseline Road Apt 2202
Boulder,   80303
United States

Abstract Text:
The mechanism of anomalous electron heat transport in tokamaks is currently not well-understood. In fluid models, the zonal flow generation by electron-temperature-gradient (ETG) turbulence is shown to be much weaker than that of similar ion ITG turbulence, leading to the expectation of a saturated state characterized by radially-elongated streamers at electron-gyroradius scales. However, gyrokinetic electron-scale simulations have shown that zonal flow (ZF) modes can contribute to long-time-scale behavior by breaking up these streamers into isotropic eddies. Recently,
a toroidal, gyrokinetic-electron theory [1] has shown that, as the ETG spectrum cascades downward, a stronger Navier-Stokes type nonlinearity couples the intermediate-scale ETG and ZF modes, thus allowing for relevant ZF generation. We provide electron-scale, gyrokinetic, two-species simulation results from GENE, a 5-d gyrokinetic continuum code, with both single-mode ETG and full ETG
spectra results comparing to the aforementioned theory. We will specifically look at the strength of ZF generation via ETG modes at intermediate and short-wavelength scales, as well as the role of
collisions in affecting the steady state.

[1] Haotian Chen et al 2021 Nucl. Fusion 61 066017