Turbulent Particle Transport in Magnetized Plasmas

Abstract

Particle transport in magnetized plasmas is investigated with a fluid model of drift wave turbulence. An analytical calculation shows that magnetic field curvature and thermodiffusion drive an anomalous pinch. The curvature driven pinch velocity is consistent with the prediction of turbulence equipartition theory. The thermodiffusion flux is found to be directed inward for a small ratio of electron to ion pressure gradient, and it reverses its sign when increasing this ratio. Numerical simulations confirm that a turbulent particle pinch exists. It is mainly driven by curvature for equal ion and electron heat sources. The sign and relative weights of the curvature and thermodiffusion pinches are consistent with the analytical calculation.

Up-gradient particle flux in a drift wave-zonal flow system

“…11 Therefore, one is tempted to invoke a simple localized linear KH instability. However, two observations weigh against interpreting the up-gradient flux in terms of a simple local linear KH.…”

“…3 In magnetically confined plasmas, up-gradient transport mechanisms have been invoked to explain the observed time-averaged plasma density and temperature profiles in astrophysical and near-Earth space plasmas [4][5][6][7][8][9] and in controlled fusion confinement experiments. [10][11][12][13][14][15] For fusion systems, inferred transport fluxes are often decomposed into an inward-directed turbulent pinch and down-gradient diffusive transport components (both of which are attributed to a combination of density and temperature gradients) that then compete to form the plasma equilibrium. In a few cases, direct measurements of net inward turbulent particle fluxes have been reported during or shortly after the formation of transport barriers associated with the formation of a suitably strong E Â B shear layer [16][17][18][19] or during the application of an externally forced E Â B shear flow.…”

Anomalous pinch of turbulent plasmas driven by the magnetic-drift-induced Lorentz force through the Stokes-Einstein relation

“…Since the neoclassical Ware pinch velocity [2] is insufficient to interpret the related experimental observations on particle pinch, anomalous trapped particle pinch due to the inhomogeneity of magnetic field strength is proposed by using the fluid model [3] and by invoking the turbulence equipartition (TEP) theory based on the invariant measure [4]; this anomalous trapped particle pinch has been confirmed by numerical simulations [5]. However, since the TEP theory of trapped electron pinch depends on the longitudinal invariant, it is not clear whether it applies to the trapped ions and passing particles, and the ambipolarity issue is unresolved [6].…”

Overview of experimental results on HL-2A

“…The change of the sign for the convective velocity may be explained with the turbulence TEM/ITG regimes [10,11]. The density threshold may be correlated to the TEM/ITG transition via the collisionality.…”