Time-dependent probability density function analysis of H-mode transitions

¹ Blackett Laboratory, Imperial College London - London, SW7 2BW, UK
² Cavendish Laboratory, University of Cambridge - JJ Thomson Avenue, Cambridge, CB3 0HE, UK
³ Department of Physics, University of Warwick - Coventry, CV4 7AL, UK
⁴ Fluid and Complex System Research Centre, Coventry University - Coventry, CV1 2TT, UK
⁵ Department of Physics and Astronomy, University of California Los Angeles - Los Angeles, CA 90095, USA
⁶ University of Wisconsin-Madison - Madison, WI 53706-1687, USA

^(a) E-mail: y.andrew@imperial.ac.uk (corresponding author)

Received: 4 January 2023
Accepted: 26 May 2023

Abstract

The first application of time-dependent probability density function (PDF) analysis to the L-H transition in fusion plasmas is presented. PDFs are constructed using Doppler Backscattering data of perpendicular fluctuation velocity, , and turbulence from the edge region of the DIII-D tokamak. These raw time-series data are sliced into millisecond-long sliding time-windows to create PDFs. During the transition, the PDFs develop strong right tails, indicative of turbulence-suppressing localised flows in the plasma edge; such features and other subtle behaviours are explored using novel information geometry techniques. This letter examines the applicability of these techniques to predict L-H transitions and investigate predator-prey self-regulation theories between turbulence and perpendicular velocity.