Speaker
Fryderyk Wilczynski
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1019.pdf
Edge-SOL stability: a two-layer approach
F. Wilczynski1 , D.W. Hughes1 , S. Van Loo1 , F. Millitelo2 , W. Arter2
1 University of Leeds, United Kingdom
2 Culham Centre for Fusion Energy, Abingdon, United Kingdom
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 full un-
derstanding of the mechanisms behind the transport in the edge of the plasma.
Study of the formation and expulsion of filaments requires consideration of both the core
and the SOL region. 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 inclusion of parallel
loss terms in the SOL region. The resulting sharp transition between the two regions imposes a
number of continuity conditions that need to be satisfied at the separatrix.
In this contribution, we study the stability of the boundary plasma by considering a two di-
mensional interchange model that includes a simple description of open and closed field line
regions based on the sheath dissipation closure. We calculate the linear stability threshold and
characterise the onset of instability. Furthermore, we discuss how the stability threshold is af-
fected subject to changes in our model, such as varying the separatrix location, or different
choices of boundary conditions.
