Ginzburg-Landau Model in a Finite Shear-Layer and Onset of Transport Barrier Nonlinear Oscillations: A Paradigm for Type-III ELMs

Abstract

We study a Reaction-Diffusion model describing the nonlinear oscillations of a transport barrier in a finite shear-layer (width dE << a), where a is the plasma minor radius, based on a 1D reduced model derived to explain nonlinear barrier oscillations in 3D turbulence simulations [P. Beyer, S. Benkadda, G. Fuhr-Chaudier et al., Phys. Rev. Lett. 94, 105001 (2005)]. We show that this single nonlinear equation encompasses most of the physics of these barrier relaxations. The nonlinear oscillations have common characteristics with type-III edge localized modes (ELMs), such as a repetition frequency which decreases with increasing power. In addition to the flow shear, the shear-layer width is also shown to control the nature of the oscillations. ((c) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)