Selective formation of turbulent structures in magnetized cylindrical plasmas

Abstract

The mechanism of nonlinear structural formation has been studied with a three-field reduced fluid model, which is extended to describe the resistive drift wave turbulence in magnetized cylindrical plasmas. In this model, ion-neutral collisions strongly stabilize the resistive drift wave, and the formed structure depends on the collision frequency. If the collision frequency is small, modulational coupling of unstable modes generates a zonal flow. On the other hand, if the collision frequency is large, a streamer, which is a localized vortex in the azimuthal direction, is formed. The structure is generated by nonlinear wave coupling and is sustained for a much longer duration than the drift wave oscillation period. This is a minimal model for analyzing the turbulent structural formation mechanism by mode coupling in cylindrical plasmas, and the competitive nature of structural formation is revealed. These turbulent structures affect particle transport.

Formation mechanism of steep wave front in magnetized plasmas

“…The ionneutral collision frequency in has the stabilization effect of the resistive drift wave and is also related to zonal flow damping, which gives a selection rule of turbulent structure formation such as zonal flows and streamers. 3 Simulations are carried out with a time independent particle source, whose profile is given as…”

“…1,2 There exist zonal flows and streamers, which suppress and enhance the transport, respectively, in meso-scale structures, and their selection rule has been investigated. 1, 3 Large scale vortex has been found to be also driven by turbulence. [4][5][6][7] Other nonlinear coherent structures formed by the drift waves, such as drift solitons, have been studied.…”

Probability Density Function of Density Fluctuations in Cylindrical Helicon Plasmas

“…In the Large Mirror Device Upgrade (LMD-U), the fluctuation spectra change depending on the neutral pressure because of drift wave damping through collisions with neutral particles [9][10][11]. In this paper, we report differences in the radial profiles of the density fluctuation PDF in two different turbulent states.…”

Phenomenological Classification of Turbulence States in Linear Magnetized Plasma PANTA

“…The streamer structure was initially predicted by an analytical study that exhibited importance of the nonlinear coupling between drift waves and a nonlinearly excited global mode the so-called mediator [11]. Dedicated studies for analyzing the nonlinear coupling in density fluctuations demonstrated the reliability of the predicted model [6][7][8]12]. Moreover, a selection rule between the streamers and the zonal flows was proposed in numerical simulation study, showing the importance of the ionneutral collisional damping of drift waves [7,8].…”

“…In particular, a set of experiments using linear devices such as the Large Mirror Device (LMD), the Large Mirror Device-Upgrade (LMD- The streamer is characterized by a structure radially stretched and azimuthally localized, as reported in Refs. [6][7][8]. The existence of the streamers in magnetically confined plasmas is foreseen to reduce the plasma performance, since the streamers act as a radially elongated large convective cell.…”