A simple shearless model for collisional drift waves in low-temperature plasmas is analyzed to point at fluctuation-induced anomalous plasma transport. Spatially coherent structures do play an important role in the particle transport beyond a critical magnetic field strength. The transition from collisional to fluctuation-induced transport is investigated. Special emphasis is put on analytical models for understanding the transition. The results from numerical simulations are interpreted.

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After a review of more or less systematic approaches for normal as well as anomalous particle transport phenomena across a magnetic field, simplified macroscopic models are discussed. A reduced two-field model for collision-dominated low-temperature plasmas is presented. Although it looks similar to its high-temperature analogue (known as the Hasegawa-Wakatani equations), it has significant peculiarities which are discussed in detail. Some basic results following from the reduced two-field model, e.g. anomalous transport scaling close to the onset of collisional driftwave instability, are discussed. General OutlineClassical radial particle transport (perpendicular to an external magnetic field) is a detailed theoretical prediction which is hardly found to be true in experimental situations. Despite the sometimes lengthy algebra used in classical collisional transport theory, the resulting scaling is easy to understand. When, e.g., applying random walk arguments, the classical (collisional) diffusion coefficient D can be estimated as [l] .where A z is the (onedimensional) distance between two successive collisions occuring at times t and t + A t . Here, for simplicity, we have used a one-dimensional formulation.Without an external magnetic field, or for displacements along (11) an external magnetic field, we can rewrite expression (1) as where wt is the thermal velocity, and v is the collision frequency. Thus, obviously, collisions hinder a sc-called parallel transport. The situation is opposite for the particle transport across (I) an external magnetic field, since then the step size A x is of the order of the (thermal) Larmor radius e of a particle gyrating around a field line. We find DI x 4 e 2 v ,') Present address:

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