An overview of dynamical methods for studying transitions between states in sheared plasma flows

Abstract

The self-organization of structures in a tokamak plasma as it undergoes an H -mode transition shows properties similar to simpler shear flow configurations. We will describe recent dynamical studies of plasma shear flows, including the idea of tracking the edge of chaos that separates two bistable states, computing the nonlinear minimal seed that can lead to turbulence, finding the attractor solution on the edge and seeing how starting from this solution we can understand the stability of relative period orbits that permeate the turbulent basin of attraction. We present a modus operandi developed for these simple configurations that can be adapted to understand the H -mode transition. This article is part of a discussion meeting issue ‘H-mode transition and pedestal studies in fusion plasmas’.