Sandpiles, silos and tokamak phenomenology: a brief review

Increasing attention is being given to the possibility that some key features of tokamak confinement physics may not be specific to the plasma state. In particular, there appear to be parallels between sandpiles and transport in tokamaks. Aspects of sandpile physics involving self-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 range of confinement physics displayed by sandpiles (in particular, by real experimental sandpiles) and also by related systems such as silos is substantially broader than so far considered for application to tokamak plasmas. It is reviewed in this paper, and additional candidate phenomena for sandpile modelling in tokamak physics, such as edge-localized modes and Berk-Breizman dynamics, are identified. The behaviour of sandpile-like systems is varied, and is sometimes sensitive to details in the experimental set-up or the theoretical model, so the role of SOC is not entirely clear. Recent theoretical progress in the modelling of experimental sandpiles is described, showing that the internal dynamics of a sandpile-type system may be governed by SOC even when this is not observed in the Bow of matter from the system.