Stochastic modeling of intermittent scrape-off layer plasma fluctuations

Area of Science:

• Plasma physics
• Fluid dynamics
• Statistical mechanics

Background:

• Scrape-off layer (SOL) plasma fluctuations are characterized by intermittent, large-amplitude bursts.
• These bursts are often linked to the radial transport of coherent, bloblike structures.
• Understanding these dynamics is crucial for magnetic confinement fusion.

Purpose of the Study:

• To develop a stochastic model for plasma density fluctuations in the SOL.
• To analyze the statistical properties of these fluctuations based on burst characteristics.
• To establish relationships between fluctuation moments and burst parameters.

Main Methods:

• A stochastic model representing plasma density as a sequence of bursts with fixed waveform.
• Analysis of burst events occurring according to a Poisson process.
• Derivation of probability density functions for fluctuation amplitudes under specific burst amplitude and waveform distributions.

Main Results:

• The model predicts a parabolic relationship between skewness and kurtosis moments for Poisson-distributed bursts.
• An exponential waveform and exponentially distributed burst amplitudes lead to a Gamma distribution for fluctuation amplitudes.
• The scale and shape parameters of the Gamma distribution are directly related to average burst amplitude, duration, and waiting times.

Conclusions:

• The stochastic burst model provides a framework for understanding SOL plasma fluctuations.
• The model successfully links macroscopic statistical moments to microscopic burst properties.
• This work offers insights into plasma transport and turbulence in magnetized plasmas.