Identifying low-dimensional dynamics in Type-I edge-localised-mode processes in JET plasmas

TL;DR

This study analyzes ELM sequences in JET plasmas, revealing that Type I ELMs encompass different physical processes with transitions driven by gas puffing rate, identified through low-dimensional dynamics analysis.

Contribution

It introduces a method to identify transitions in ELM dynamics using delay time plots, highlighting different underlying processes within Type I ELMs based on gas puffing rate.

Findings

Transitions between ELMing processes are driven by gas puffing rate.

Delay time plots reveal distinct phase space dynamics.

Type I ELMs include multiple underlying physical processes.

Abstract

Edge localised mode (ELM) measurements from reproducibly similar plasmas in the Joint European Torus (JET) tokamak, which differ only in their gas puffing rate, are analysed in terms of the pattern in the sequence of inter-ELM time intervals. It is found that the category of ELM defined empirically as Type I - typically more regular, less frequent, and having larger amplitude than other ELM types - embraces substantially different ELMing processes. By quantifying the structure in the sequence of inter-ELM time intervals using delay time plots, we reveal transitions between distinct phase space dynamics, implying transitions between distinct underlying physical processes. The control parameter for these transitions between these different ELMing processes is the gas puffing rate.