Impact of Resonant Magnetic Perturbations on Zonal Modes, Drift-Wave Turbulence and the L-H Transition Threshold

TL;DR

This paper models how Resonant Magnetic Perturbations influence turbulence, flow, and the L-H transition in plasma confinement, predicting increased power thresholds and decreased hysteresis, with implications for understanding density pump-out effects.

Contribution

It introduces a zero-dimensional predator-prey model coupling drift-wave turbulence with RMP effects, predicting novel transport bifurcations and detailed L-H transition behavior under RMP influence.

Findings

Both L-I and I-H power thresholds increase with RMP amplitude.

RMPs decrease the hysteresis between forward and back L-H transitions.

Density profiles exhibit increased turbulent diffusion with RMPs, explaining density pump-out.

Abstract

We study the effects of Resonant Magnetic Perturbations (RMPs) on turbulence, flows and confinement in the framework of resistive drift-wave turbulence. This work was motivated, in parts, by experiments reported at the IAEA 2010 conference [Y. Xu {\it et al}, Nucl. Fusion \textbf{51}, 062030] which showed a decrease of long-range correlations during the application of RMPs. We derive and apply a zero-dimensional predator-prey model coupling the Drift-Wave Zonal Mode system [M. Leconte and P.H. Diamond, Phys. Plasmas \textbf{19}, 055903] to the evolution of mean quantities. This model has both density gradient drive and RMP amplitude as control parameters and predicts a novel type of transport bifurcation in the presence of RMPs. This model allows a description of the full L-H transition evolution with RMPs, including the mean sheared flow evolution. The key results are: i) The L-I and I-H power thresholds \emph{both} increase with RMP amplitude $|\bx|$, the relative increase of the L-I threshold scales as $\Delta P_{\rm LI} \propto |\bx|^2 \nu_*^{-2} \gyro^{-2}$, where $\nu_*$ is edge collisionality and $\gyro$ is the sound gyroradius. ii) RMPs are predicted to \emph{decrease} the hysteresis between the forward and back-transition. iii) Taking into account the mean density evolution, the density profile - sustained by the particle source - has an increased turbulent diffusion compared with the reference case without RMPs which provides one possible explanation for the \emph{density pump-out} effect.