Helical self-organization in 3D MHD modelling of fusion plasmas: plasma flow effects and Alfvén waves detection

Self-organized helical states are a ubiquitous feat ure in astrophysical and magnetic confinement curre nt carrying plasmas. In the reversed-field pinch toroi dal plasmas quasi-helical states are observed both in high current experiments [1] and in nonlinear magne tofluid numerical simulations [2]. In the tokamak helical self-organization is an essential part of t he dynamics in advanced regimes [3]. In this work w e show two main advancements in our 3D nonlinear visc o-resistive magnetohydrodynamic (MHD) studies. First, we study the effect of a macroscopi c plasma rotation on helical states, to model both reversed-field pinches and tokamaks: in particular, we analyze the interaction between an external momentum source and/or seed magnetic perturbations (MPs), both static and rotating. We find the expected interplay between plasma rotation and appl ied MPs in tokamaks [4] confirming MPs screening over a threshold in normalized plasma rot ation. We then focus on the reversed-field pinch case: starting from previous works [5,6,7], where i t is shown that a mean flow arises from and interac ts with nonlinearly coupled kink/tearing modes, and th en introducing a momentum source, we analyse the impact of mean plasma flow on self-organized helica l regimes. Our modelling indicates that an external momentum source of sufficiently high intensity can prevent the formation of a helical state, while a moderate one is compatible with a slight enhancemen t of the intensity of the helical state. We present a novel study in the realistic cases [2] of experimen tal-like helical states stimulated by MPs: the pres ence of a plasma flow, previously not considered, introd uces quantitative changes to their properties. As a final novelty, we here also show (for the first tim e) that the typical intermittency with reconnection events displayed in the RFP helical self-organizati on process is accompanied by the excitation of both compressional and shear Alfvén waves, in reasonable agreement with experimental measurement [8].