Burst statistics of fluctuations in a simple magnetized torus configuration

TL;DR

This study analyzes turbulence-induced fluctuations in a simple magnetized torus, revealing intermittent behavior and chaotic dynamics through statistical and multifractal analysis of experimental data.

Contribution

It provides new insights into the spatial and temporal structure of turbulence and chaos in a toroidal plasma using detailed statistical methods.

Findings

Intermittent fluctuations characterized by probability density functions.

Multifractal spectra reveal complex turbulence regimes.

Global potential fluctuations linked to low-dimensional chaos.

Abstract

In a toroidal plasma confined by a purely toroidal magnetic field the plasma transport is governed by electrostatic turbulence driven by the flute interchange instability on the low-field side of the torus cross section. In this paper we revisit experimental data obtained from the Blaamann torus at the University of Tromso. On time-scales shorter than the poloidal rotation time, the time series of potential and electron density fluctuations measured on stationary Langmuir probes essentially reflect the spatial poloidal structure of the turbulent field (Taylor hypothesis). On these time scales the signals reveals an intermittent character exposed via analysis of probability density functions and computation of multifractal dimension spectra in different regimes of time scales. This intermittency is associated with the shape and distribution of pronounced spikes in the signal. On time scales much longer than the rotation period there are strong global fluctuations in the plasma potential which are shown to to be the result of low-dimensional chaotic dynamics.