Characterizing electron temperature gradient turbulence via numerical simulation

Numerical simulations of electron temperature gradient (ETG) turbulence are presented that characterize the ETG fluctuation spectrum, establish limits to the validity of the adiabatic ion model often employed in studying ETG turbulence, and support the tentative conclusion that plasma-operating regi...

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Bibliographic Details
Published in:Physics of plasmas 2006-12, Vol.13 (12)
Main Authors: Nevins, W. M., Candy, J., Cowley, S., Dannert, T., Dimits, A., Dorland, W., Estrada-Mila, C., Hammett, G. W., Jenko, F., Pueschel, M. J., Shumaker, D. E.
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
CONVERGENCE
CORRELATION FUNCTIONS
ELECTRON TEMPERATURE
ELECTRONS
FLUCTUATIONS
HEAT FLUX
HEAT TRANSFER
ION TEMPERATURE
IONS
MAGNETIC FIELDS
NUMERICAL ANALYSIS
PLASMA
PLASMA CONFINEMENT
PLASMA SIMULATION
RADIATION TRANSPORT
SHEAR
TEMPERATURE GRADIENTS
TOKAMAK DEVICES
TURBULENCE
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Summary:Numerical simulations of electron temperature gradient (ETG) turbulence are presented that characterize the ETG fluctuation spectrum, establish limits to the validity of the adiabatic ion model often employed in studying ETG turbulence, and support the tentative conclusion that plasma-operating regimes exist in which ETG turbulence produces sufficient electron heat transport to be experimentally relevant. We resolve prior controversies regarding simulation techniques and convergence by benchmarking simulations of ETG turbulence from four microturbulence codes, demonstrating agreement on the electron heat flux, correlation functions, fluctuation intensity, and r m s flow shear at fixed simulation cross section and resolution in the plane perpendicular to the magnetic field. Excellent convergence of both continuum and particle-in-cell codes with time step and velocity-space resolution is demonstrated, while numerical issues relating to perpendicular (to the magnetic field) simulation dimensions and resolution are discussed. A parameter scan in the magnetic shear, s , demonstrates that the adiabatic ion model is valid at small values of s ( s < 0.4 for the parameters used in this scan) but breaks down at higher magnetic shear. A proper treatment employing gyrokinetic ions reveals a steady increase in the electron heat transport with increasing magnetic shear, reaching electron heat transport rates consistent with analyses of experimental tokamak discharges.
ISSN:1070-664X
1089-7674
DOI:10.1063/1.2402510