Stochastic fluctuation and transport of tokamak edge plasmas with the resonant magnetic perturbation field

TL;DR

This paper uses Complexity-Entropy analysis to differentiate between stochastic and chaotic plasma fluctuations in tokamak edge plasmas under resonant magnetic perturbations, revealing insights into ELM suppression mechanisms.

Contribution

It introduces the application of Complexity-Entropy analysis to characterize plasma turbulence and flux during RMP ELM control, highlighting the role of stochastic fluctuations near the pedestal top.

Findings

Stochastic pedestal top temperature fluctuations distinguish RMP ELM suppression from natural ELM phases.

Narrow layer of field penetration near the pedestal top may cause localized stochastic temperature fluctuations.

Stronger plasma response to RMP increases stochasticity in ion saturation current measurements.

Abstract

We present that a statistical method known as the Complexity-Entropy analysis is useful to characterize a state of plasma turbulence and flux in the resonant magnetic perturbation (RMP) edge localized mode (ELM) control experiment. The RMP ELM suppression phase with the stochastic pedestal top temperature fluctuation can be distinguished from the natural ELM free phase with the chaotic fluctuation. It is discussed that the stochastic temperature fluctuation localized near the pedestal top can be originated from the narrow layer of the field penetration near the pedestal top. The forced magnetic island can emit the resonant drift wave of comparable sizes (relatively low-k) in the RMP ELM suppression phase, and it can results in the generation of stochastic higher wavenumber fluctuations coupled to tangled fields around the island. The analysis of the ion saturation current measurement around the main outer striking point on the divertor shows that it also becomes more stochastic as the stronger plasma response to the RMP field is expected.