Speaker
Description
See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1044.pdf
In magnetic confinement devices, the boundary turbulence is characterised by intermittent ejection of coherent filamentary structures. These filaments transport plasma from the well-confined core region, through the Scrape-Off Layer (SOL), towards the material surfaces. This results in increased plasma-wall interaction, which has the potential to damage plasma-facing components and shorten the lifetime of the device. It is therefore essential to develop a full understanding of the mechanisms behind the transport in the edge of the plasma.
A good candidate for the mechanism responsible for the scrape-off layer fluctuations is the interchange instability. SOL interchange models have been studied extensively both theoretically and numerically, and have provided useful insight into the dynamics of SOL plasma. Subsequently, motivated by the concept that filaments are generated in the core region before being ejected into the SOL, the simple SOL models have been extended to consider a configuration composed of the two regions (core and SOL) connected at the interface. The two regions exhibit distinct dynamics parallel to the magnetic field. In the core, field lines are considered periodic in the parallel direction, while in the SOL, the field lines end with a Debye sheath at a material surface. The presence of the sheath provides a sink for plasma particles and energy. Mathematically, this is represented by the inclusion of parallel loss terms in the SOL region. Although such two-region models have become fairly standard in numerical modelling of filament generation, their linear stability properties have not been explored.
The fundamental mechanism of interchange drive in edge plasma has been compared to that of buoyancy drive in neutral fluids, with reference to Rayleigh-Bénard convection in particular. Indeed, simple SOL interchange models can be viewed as a modified convection problem. By extension, there is a similar analogy between two-region plasma models and two-layer convection. Two layer convection has attracted considerable attention because of its interesting theoretical aspects and a variety of possible convection modes. One of these is the possibility of the onset of two distinct unstable modes at the same value of Rayleigh number.
In this contribution address we investigate whether a similar situation can occur in the two-region plasma models through a linear stability analysis of a two dimensional interchange model that includes a simple description of open and closed field line regions based on the sheath dissipation closure.
