SANDPILES, SILOS AND TOKAMAK PHENOMENOLOGY - A BRIEF REVIEW

Increasing attention is being given to the possibility that some key f eatures of tokamak confinement physics may not be specific to the plas ma state. In particular, there appear to be parallels between sandpile s and transport in tokamaks. Aspects of sandpile physics involving sel f-organized criticality (SOC) have been suggested by Carreras, Diamond , Newman and co-workers (for example, 1996 Phys. Plasmas 3 1858, 2903 and 3745) as a paradigm for certain tokamak phenomena. However, the ra nge of confinement physics displayed by sandpiles (in particular, by r eal experimental sandpiles) and also by related systems such as silos is substantially broader than so far considered for application to tok amak plasmas. It is reviewed in this paper, and additional candidate p henomena for sandpile modelling in tokamak physics, such as edge-local ized modes and Berk-Breizman dynamics, are identified. The behaviour o f sandpile-like systems is varied, and is sometimes sensitive to detai ls in the experimental set-up or the theoretical model, so the role of SOC is not entirely clear. Recent theoretical progress in the modelli ng of experimental sandpiles is described, showing that the internal d ynamics of a sandpile-type system may be governed by SOC even when thi s is not observed in the Bow of matter from the system.