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

The extended Hasegawa-Wakatani equations generate fully nonlinear self-consistent solutions for coupled density n and vorticity del(2)phi, where phi is electrostatic potential, in a plasma with background density inhomogeneity kappa=-partial derivative ln n(0)/partial derivative x and magnetic field strength inhomogeneity C=-partial derivative ln B/partial derivative x. Finite C introduces interchange effects and del B drifts into the framework of drift turbulence through compressibility of the ExB and diamagnetic drifts. This paper addresses the direct computation of the radial ExB density flux Gamma(n)=-n partial derivative phi/partial derivative y, tracer particle transport, the statistical properties of the turbulent fluctuations that drive Gamma(n) and tracer motion, and analytical underpinnings. Systematic trends emerge in the dependence on C of the skewness of the distribution of pointwise Gamma(n) and in the relative phase of density-velocity and density-potential pairings. It is shown how these effects, together with conservation of potential vorticity Pi=del(2)phi-n+(kappa-C)x, account for much of the transport phenomenology. Simple analytical arguments yield a Fickian relation Gamma(n)=(kappa-C)D-x between the radial density flux Gamma(n) and the radial tracer diffusivity D-x, which is shown to explain key trends in the simulations.