Stochastic modelling of intermittent scrape-off layer plasma fluctuations

TL;DR

This paper introduces a stochastic model for plasma fluctuations in the scrape-off layer, capturing burst dynamics and their statistical properties, including skewness, kurtosis, and amplitude distributions, relevant for understanding plasma behavior in magnetic confinement devices.

Contribution

It presents a novel stochastic framework modeling plasma fluctuations as bursts with fixed waveforms, predicting statistical relations and amplitude distributions under general conditions.

Findings

Predicts a parabolic skewness-kurtosis relation for plasma fluctuations.

Derives a Gamma distribution for fluctuation amplitudes with specific parameters.

Applicable to modeling intermittent plasma behavior in magnetic confinement.

Abstract

Single-point measurements of fluctuations in the scrape-off layer of magnetized plasmas are generally found to be dominated by large-amplitude bursts which are associated with radial motion of blob-like structures. A stochastic model for these fluctuations is presented, with the plasma density given by a random sequence of bursts with a fixed wave form. Under very general conditions, this model predicts a parabolic relation between the skewness and kurtosis moments of the plasma fluctuations. In the case of exponentially distributed burst amplitudes and waiting times, the probability density function for the fluctuation amplitudes is shown to be a Gamma distribution with the scale parameter given by the average burst amplitude and the shape parameter given by the ratio of the burst duration and waiting times.