Chaotic edge density fluctuations in the Alcator C-Mod tokamak

TL;DR

This study demonstrates that turbulent edge density fluctuations in the Alcator C-Mod tokamak are chaotic, using spectral, probabilistic, and complexity-entropy analyses, which may influence understanding of turbulent transport.

Contribution

It provides the first evidence that edge turbulence in Alcator C-Mod is chaotic based on multiple analytical methods, advancing the understanding of plasma turbulence.

Findings

Edge density fluctuations exhibit exponential power spectra.

Probability distributions align with Lorentzian pulses.

Signal positions indicate chaotic dynamics on the complexity-entropy plane.

Abstract

Analysis of the time series obtained with the O-Mode reflectometer (Rhodes et al 1997 Plasma Phys. and Control. Fusion 40 (1998) 493-510) and the gas puff imaging (Cziegler, I. et al 2010 Phys. of Plasmas 17, No. 5 (2010) 056120) systems on the Alcator C-Mod tokamak reveals that the turbulent edge density fluctuations are chaotic. Supporting evidence for this conclusion includes: the observation of exponential power spectra (which is associated with Lorentzian-shaped pulses in the time series), the population of the corresponding Bandt-Pompe probability distributions (Bandt and Pompe 2002 Phys. Rev. Lett. 88 174102), and the location of the signal on the complexity-entropy plane (C-H plane) (Rosso et al 2007 Phys. Rev. Lett. 99, 154102 (2007)). The classification of edge turbulence as chaotic opens the door for further work to understand the underlying process and the impact on turbulent transport.