A Nonlinear Dynamics Characterization of The Scrape-off Layer Plasma Fluctuations

TL;DR

This paper models the plasma density fluctuations in the scrape-off layer using a stochastic differential equation with quadratic nonlinearity, matching experimental distributions and revealing the role of nonlinear dynamics in intermittency.

Contribution

It introduces a novel stochastic model for plasma density fluctuations incorporating quadratic nonlinearity, aligning theoretical predictions with experimental data.

Findings

The model accurately reproduces the experimental distribution of plasma fluctuations.

Quadratic nonlinearity explains the intermittency observed in plasma turbulence.

The gamma distribution aligns with the nonlinear stochastic model's predictions.

Abstract

A stochastic differential equation for the plasma density dynamics is derived, consistent with the experimentally measured distribution and the theoretical quadratic nonlinearity. The plasma density is driven by a multiplicative Wiener process and evolves on the turbulence correlation time scale, while the linear growth is quadratically damped by the fluctuation level. The sensitivity of intermittency to the nonlinear dynamics is investigated by analyzing the Langevin representation of two intermittent distributions, showing the agreement between the quadratic nonlinearity and the gamma distribution.