A sandpile model with tokamak-like enhanced confinement phenomenology.pdf

a r X i v : p h y s i c s / 0 0 1 0 0 3 2 v 2 [ p h y s i c s .p l a s m - p h ] 2 F e b 2 0 0 1 HEP/123-qed A sandpile model with tokamak-like enhanced confinement phenomenology S. C. Chapman1?, 1Physics Dept. Univ. of Warwick, Coventry CV4 7AL, UK R. O. Dendy2 2EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB, United Kingdom B. Hnat1 (February 9, 2008) Abstract Confinement phenomenology characteristic of magnetically confined plas- mas emerges naturally from a simple sandpile algorithm when the parameter controlling redistribution scalelength is varied. Close analogues are found for enhanced confinement, edge pedestals, and edge localised modes (ELMs), and for the qualitative correlations between them. These results suggest that toka- mak observations of avalanching transport are deeply linked to the existence ?sandrac@astro.warwick.ac.uk 1 of enhanced confinement and ELMs. 52.55.Dy, 52.55.Fa, 45.70.Ht, 52.35.Ra Typeset using REVTEX 2 The introduction of the sandpile paradigm [1]- [3] into magnetized plasma physics (fusion [4]- [12], magnetospheric [13]- [15], and accretion disk [16]- [18]: for recent reviews see Ref. [19,20]) has opened new conceptual avenues. It provides a framework within which observa- tions of rapid nondiffusive nonlocal transport phenomena can be studied; recent examples include analyses of auroral energy deposition derived from global imaging [15], and of elec- tron temperature fluctuations in the DIII-D tokamak [12], both of which involve avalanching. Insofar as such phenomena resemble those in experimental sandpiles or mathematically ide- alized models thereof, they suggest that the confinement physics of macroscopic systems (plasma and other) may reflect unifying underlying principles. In this paper we present results suggesting that this unity may extend to some of the most distinctive features of toroidal magnetic plasma confinement: enhanced confinement regimes (“H-modes”), edge localised