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Finite Larmor radius effects on $\boldsymbol{E}\times \boldsymbol{B}$ weak turbulence transport

Part of: Focus on Fusion

Published online by Cambridge University Press:  01 May 2018

N. Kryukov ,
J. J. Martinell  and
D. del-Castillo-Negrete
N. Kryukov
Affiliation:
Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, A. Postal 70-543, 04510 Mexico D. F., Mexico
J. J. Martinell*
Affiliation:
Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, A. Postal 70-543, 04510 Mexico D. F., Mexico
D. del-Castillo-Negrete
Affiliation:
Oak Ridge National Laboratory, Oak Ridge, TN 37831-8071, USA
*
†Email address for correspondence: [email protected]
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Abstract

Transport of test particles in two-dimensional weak turbulence with waves propagating along the poloidal direction is studied using a reduced model. Finite Larmor radius (FLR) effects are included by gyroaveraging over one particle orbit. For low wave amplitudes the motion is mostly regular with particles trapped in the potential wells. As the amplitude increases the trajectories become chaotic and the Larmor radius modifies the orbits. For a thermal distribution of Finite Larmor radii the particle distribution function (PDF) is Gaussian for small $\unicode[STIX]{x1D70C}_{th}$ (thermal gyroradius) but becomes non-Gaussian for large $\unicode[STIX]{x1D70C}_{th}$. However, the time scaling of transport is diffusive, as characterized by a linear dependence of the variance of the PDF with time. An explanation for this behaviour is presented that provides an expression for an effective diffusion coefficient and reproduces the numerical results for large wave amplitudes which implies generalized chaos. When a shear flow is added in the direction of wave propagation, a modified model is obtained that produces free-streaming particle trajectories in addition to trapped ones; these contribute to ballistic transport for low wave amplitude but produce super-ballistic transport in the chaotic regime. As in the previous case, the PDF is Gaussian for low $\unicode[STIX]{x1D70C}_{th}$ becoming non-Gaussian as it increases. The perpendicular transport presents the same behaviour as in the case with no flow but the diffusion is faster in the presence of the flow.

Keywords

plasma confinementplasma nonlinear phenomena
Type
Research Article
Information
Journal of Plasma Physics , Volume 84 , Issue 3 , June 2018 , 905840301
Copyright
© Cambridge University Press 2018 

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