skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Stellarator microinstabilities and turbulence at low magnetic shear

Abstract

Gyrokinetic simulations of drift waves in low-magnetic-shear stellarators reveal that simulation domains comprised of multiple turns can be required to properly resolve critical mode structures important in saturation dynamics. Marginally stable eigenmodes important in saturation of ion temperature gradient modes and trapped electron modes in the Helically Symmetric Experiment (HSX) stellarator are observed to have two scales, with the envelope scale determined by the properties of the local magnetic shear and an inner scale determined by the interplay between the local shear and magnetic field-line curvature. Properly resolving these modes removes spurious growth rates that arise for extended modes in zero-magnetic-shear approximations, enabling use of a zero-magnetic-shear technique with smaller simulation domains and attendant cost savings. Analysis of subdominant modes in trapped electron mode (TEM)-driven turbulence reveals that the extended marginally stable modes play an important role in the nonlinear dynamics, and suggests that the properties induced by low magnetic shear may be exploited to provide another route for turbulence saturation.

Authors:
ORCiD logo; ; ; ;
Publication Date:
Research Org.:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1544194
Resource Type:
Journal Article
Journal Name:
Journal of Plasma Physics
Additional Journal Information:
Journal Volume: 84; Journal Issue: 5; Journal ID: ISSN 0022-3778
Publisher:
Cambridge University Press
Country of Publication:
United States
Language:
English

Citation Formats

Faber, B.  J., Pueschel, M.  J., Terry, P.  W., Hegna, C.  C., and Roman, J.  E. Stellarator microinstabilities and turbulence at low magnetic shear. United States: N. p., 2018. Web. doi:10.1017/S0022377818001022.
Faber, B.  J., Pueschel, M.  J., Terry, P.  W., Hegna, C.  C., & Roman, J.  E. Stellarator microinstabilities and turbulence at low magnetic shear. United States. doi:10.1017/S0022377818001022.
Faber, B.  J., Pueschel, M.  J., Terry, P.  W., Hegna, C.  C., and Roman, J.  E. Mon . "Stellarator microinstabilities and turbulence at low magnetic shear". United States. doi:10.1017/S0022377818001022.
@article{osti_1544194,
title = {Stellarator microinstabilities and turbulence at low magnetic shear},
author = {Faber, B.  J. and Pueschel, M.  J. and Terry, P.  W. and Hegna, C.  C. and Roman, J.  E.},
abstractNote = {Gyrokinetic simulations of drift waves in low-magnetic-shear stellarators reveal that simulation domains comprised of multiple turns can be required to properly resolve critical mode structures important in saturation dynamics. Marginally stable eigenmodes important in saturation of ion temperature gradient modes and trapped electron modes in the Helically Symmetric Experiment (HSX) stellarator are observed to have two scales, with the envelope scale determined by the properties of the local magnetic shear and an inner scale determined by the interplay between the local shear and magnetic field-line curvature. Properly resolving these modes removes spurious growth rates that arise for extended modes in zero-magnetic-shear approximations, enabling use of a zero-magnetic-shear technique with smaller simulation domains and attendant cost savings. Analysis of subdominant modes in trapped electron mode (TEM)-driven turbulence reveals that the extended marginally stable modes play an important role in the nonlinear dynamics, and suggests that the properties induced by low magnetic shear may be exploited to provide another route for turbulence saturation.},
doi = {10.1017/S0022377818001022},
journal = {Journal of Plasma Physics},
issn = {0022-3778},
number = 5,
volume = 84,
place = {United States},
year = {2018},
month = {10}
}