Applying sandpiles and scaling to fusion and astrophysical plasmas: why and how?

Richard Dendy
Euratom/UKAEA Fusion Association, Culham Science Centre, United Kingdom

There is substantial evidence that simple diffusive and Gaussian paradigms for transport and turbulence in plasmas cannot describe all the experimentally observed phenomenology, both in fusion and in astrophysics. First, we consider the linkage of rapid, nonlocal, nondiffusive transport to other pulselike phenomena in tokamaks, and to global confinement. One may then seek to identify the minimal requirements for statistical processes that can generate nondiffusive avalanching transport and can reproduce the non-Gaussian features of certain density fluctuation and flux fluctuation measurements in tokamaks. It can be shown that statistical clustering of transport events, described for example in terms of negative binomial distributions, is sufficient to generate some of the observed phenomenology. Finally we describe how nonlinear time series analysis has been used to extract significant information about the scaling properties of the turbulence in the X-ray emitting plasma accretion discs of the microquasar GRS1915+105 and the black hole X-ray binary Cygnus X-1.