Simulation of plasma transport by coherent structures in scrape-off-layer tokamak plasmas

Abstract

The formation of coherent structures by two-dimensional interchange turbulence in the scrape-off layer (SOL) of tokamak plasmas and their subsequent contribution to anomalous plasma transport has been studied in recent years using electron continuity and current balance equations. In this paper, it is demonstrated that the inclusion of electron energy equation in the simulations changes the nature of coherent structures in a significant manner and gives results which are in better agreement with experiments. Specifically, it is observed that radial potential gradients are established which give a poloidal elongation and movement to the structures. Only during the radial transport events do the structures get significantly extended in the radial direction giving radial velocities of order 1 km/s. Sometimes detachment of density structures from the main plasma is observed. These detached structures either decay into the background plasma or are transported out from the SOL. The simulated particle flux and its statistical properties also are discussed.

Three-dimensional fluid simulations of a simple magnetized toroidal plasma

“…3 shows that the interchange instability dominates. We note that in the presence of sheath effects, the linear grow rate of the interchange instability is reduced at small value of k y , as noted in the analysis of the two-dimensional model [6,16]. By balancing the term γk 2 yφ and d zj|| /n 00 in Eq.…”

Plasma transport and turbulence in the Helimak: Simulation and experiment

“…͑7͒-͑9͒ are very similar to those used previously to study interchange dynamics in other systems. 4,[14][15][16] The normalized diffusion constants are taken to be n = t = 1 and = 0.5. Localized source profiles with Gaussian shapes are used for density and temperature in the simulations; 4 that is, the shapes of the sources are given by S n = S T = S 0 exp͓−͑x − x s ͒ 2 / w 2 ͔.…”

Mechanism for blob generation in the TORPEX toroidal plasma

“…The observed behavior is redolent of numerical simulations of edge/SOL turbulence in tokamaks, which show the generation of plasma blobs via shearing of density streamers by the plasma flow. 12 To illustrate the mechanism driving the elongation of the density wave crest, we show in Fig. 6͑a͒ a zoomed view of the instantaneous pattern of the fluctuating ṽ EϫB .…”