The effects of nonuniform magnetic field strength on density flux and test particle transport in drift wave turbulence

Dewhurst, J. M.; Hnat, B.; Dendy, R. O.
July 2009
Physics of Plasmas;Jul2009, Vol. 16 Issue 7, p072306
Academic Journal
The extended Hasegawa–Wakatani equations generate fully nonlinear self-consistent solutions for coupled density n and vorticity ∇2[lowercase_phi_synonym], where [lowercase_phi_synonym] is electrostatic potential, in a plasma with background density inhomogeneity κ=-∂ ln n0/∂x and magnetic field strength inhomogeneity C=-∂ ln B/∂x. Finite C introduces interchange effects and ∇B drifts into the framework of drift turbulence through compressibility of the E×B and diamagnetic drifts. This paper addresses the direct computation of the radial E×B density flux Γn=-n∂[lowercase_phi_synonym]/∂y, tracer particle transport, the statistical properties of the turbulent fluctuations that drive Γn and tracer motion, and analytical underpinnings. Systematic trends emerge in the dependence on C of the skewness of the distribution of pointwise Γn and in the relative phase of density-velocity and density-potential pairings. It is shown how these effects, together with conservation of potential vorticity Π=∇2[lowercase_phi_synonym]-n+(κ-C)x, account for much of the transport phenomenology. Simple analytical arguments yield a Fickian relation Γn=(κ-C)Dx between the radial density flux Γn and the radial tracer diffusivity Dx, which is shown to explain key trends in the simulations.


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