Zonal flow excitation in electron-scale tokamak turbulence

• Published in: Nuclear fusion Vol. 63; no. 2
• Main Authors: Tirkas, Stefan, Chen, Haotian, Merlo, Gabriele, Jenko, Frank, Parker, Scott
• Format: Journal Article
• Language: English
• Published: United States IOP Science 03-01-2023
• Subjects: Physics
• ISSN: 0029-5515

Abstract The derivation of an intermediate-scale gyrokinetic-electron theory in nonuniform tokamak plasmas (Chenet al2021Nucl. Fusion61<ext-link ext-link-type='uri' href='https://doi.org/10.1088/1741-4326/abf81a' type='simple'>066017</ext-link>) has shown that a Navier–Stokes type nonlinearity couples electron-temperature-gradient (ETG) modes and zonal flow (ZF) modes with wavelengths much shorter than the ion gyroradius but much longer than the electron gyroradius. This intermediate-scale ETG-ZF coupling is typically stronger than the Hasegawa–Mima type nonlinearity characteristic of the fluid approximation and is predicted to lead to relevant ZF generation and ETG mode regulation. Electron-scale, continuum, gyrokinetic simulation results are presented here which include both single-mode ETG and full-spectrum ETG turbulence. The ZF generation due to single ETG modes is investigated and the single-mode intermediate-scale results are found to be in agreement with theory. The full-spectrum results are then presented and explained qualitatively in terms of the single-mode results. It is found that the ETG-driven ZFs regulate intermediate-scale electron heat flux transport to levels in the predicted range.