A MINIMAL DYNAMICAL MODEL OF EDGE LOCALIZED MODE PHENOMENA

A simple, low-dimensional model of edge localized mode (ELM) phenomena is presented. ELM dynamics are determined by the interaction of few b asic processes at the edge of tokamak plasma; these include the evolut ion of magnetohydrodynamic (MHD) pressure gradient driven instabilitie s, the low-high (L-H) transition (mediated by electric field shear ind uced suppression and generation), the fueling of the edge by neutral p articles, and edge heating by thermal flux from the core plasma. In th e parameter regime characteristic of an H-mode plasma, the model exhib its a transition to stationary relaxation oscillations (i.e., stable l imit cycle behavior) corresponding to ELMs. The dependence of ELM freq uency, amplitude, etc. on the heating power P-in and other control par ameters is studied. The transition from giant to grassy ELM behavior a ppears as a consequence of increasingly marginal stability to ideal ba llooning as P-in increases. Several details of the dynamics of the ELM onset and behavior close to the L-H transition threshold are revealed , as well. (C) 1995 American Institute of Physics.