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Title: Reversal of turbulent gyroBohm isotope scaling due to nonadiabatic electron drive

Abstract

Here, the influence of kinetic electrons on the isotope scaling of gyrokinetic turbulent energy flux is assessed. A simple framework is used to study the transition from ion-dominated turbulence regimes to regimes where electron and ion transport levels are comparable. In the ion-dominated regime, the turbulent ion energy flux increases as the ion mass increases, in agreement with simple gyroBohm scaling arguments. Conversely, in the latter regime for which the influence of electrons is significant, a strong reversal from the gyroBohm scaling is observed which cannot be captured by mixing length estimates. In this reversed regime, the turbulent ion energy flux decreases as ion mass increases. The reversal is controlled by finite electron-to-ion mass-ratio dependence of the nonadiabatic electron response. This mass-ratio dependence is dominated by the parallel motion terms in the electron gyrokinetic equation, and provides a correction to the bounce-averaged electron limit which is independent of mass ratio. The finite-mass correction is larger for light ions and explains the observed gyroBohm reversal for hydrogen plasmas. Lastly, an implication is that isotope scaling may not be properly described by simplified fluid or bounce-averaged electron equations.

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]
  1. General Atomics, San Diego, CA (United States)
Publication Date:
Research Org.:
Dept. of Energy (DOE), Washington DC (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1559134
Grant/Contract Number:  
FC02-04ER54698; FG02-95ER54309; FC02-06ER54873; SC0017992
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 26; Journal Issue: 8; 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

Belli, E. A., Candy, J., and Waltz, R. E. Reversal of turbulent gyroBohm isotope scaling due to nonadiabatic electron drive. United States: N. p., 2019. Web. doi:10.1063/1.5110401.
Belli, E. A., Candy, J., & Waltz, R. E. Reversal of turbulent gyroBohm isotope scaling due to nonadiabatic electron drive. United States. doi:10.1063/1.5110401.
Belli, E. A., Candy, J., and Waltz, R. E. Tue . "Reversal of turbulent gyroBohm isotope scaling due to nonadiabatic electron drive". United States. doi:10.1063/1.5110401.
@article{osti_1559134,
title = {Reversal of turbulent gyroBohm isotope scaling due to nonadiabatic electron drive},
author = {Belli, E. A. and Candy, J. and Waltz, R. E.},
abstractNote = {Here, the influence of kinetic electrons on the isotope scaling of gyrokinetic turbulent energy flux is assessed. A simple framework is used to study the transition from ion-dominated turbulence regimes to regimes where electron and ion transport levels are comparable. In the ion-dominated regime, the turbulent ion energy flux increases as the ion mass increases, in agreement with simple gyroBohm scaling arguments. Conversely, in the latter regime for which the influence of electrons is significant, a strong reversal from the gyroBohm scaling is observed which cannot be captured by mixing length estimates. In this reversed regime, the turbulent ion energy flux decreases as ion mass increases. The reversal is controlled by finite electron-to-ion mass-ratio dependence of the nonadiabatic electron response. This mass-ratio dependence is dominated by the parallel motion terms in the electron gyrokinetic equation, and provides a correction to the bounce-averaged electron limit which is independent of mass ratio. The finite-mass correction is larger for light ions and explains the observed gyroBohm reversal for hydrogen plasmas. Lastly, an implication is that isotope scaling may not be properly described by simplified fluid or bounce-averaged electron equations.},
doi = {10.1063/1.5110401},
journal = {Physics of Plasmas},
number = 8,
volume = 26,
place = {United States},
year = {2019},
month = {8}
}

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