Speaker
Vladimir Rozhansky
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.106.pdf
Role of neoclassical mechanisms in the formation of a tokamak scrape-off
layer
V. Rozhansky1, E. Kaveeva1, I. Senichenkov1, E. Vekshina1
1
Peter the Great St.Petersburg Polytechnic University, St.Petersburg, Russia
Understanding of the mechanisms responsible for the formation of tokamak scrape-off layer
(SOL) is crucial for ITER as well as for future tokamak reactors. In particular it is necessary
to understand inverse dependence of the SOL width on the plasma current observed on
present day tokamaks. Grad B drift could be a candidate for a leading mechanism of SOL
formation as was suggested by Goldston [1]. However, the radial ion flux caused by grad B
drift should be considered together with the radial ion ExB drift as it was done in standard
neoclassical theory for closed flux surfaces, and the resulting flux is determined by ion
viscosity [2].
In the present paper role of neoclassical mechanisms in the formation of density and
electron temperature fall-off lengths is analyzed. It is shown that neoclassical mechanisms
can give SOL width of the order of ion Larmor radius multiplied by safety factor in
accordance with the observed inverse current dependence. Radial transport is followed by
flow of radial current which is short-circuited through the divertor plates. The analytics is
supported by numerical modeling of edge plasma by SOLPS5.2 code [2] with the reduced
anomalous transport coefficients in the SOL. These results are in agreement with the earlier
modeling with reduced anomalous diffusion coefficient [3].
A possibility of contribution from blob (filament) transport to the SOL formation is
also considered. It is shown that blob transport can also give inverse current dependence of
the SOL with.
[1] Goldston R J 2012 Nucl. Fusion 52 013009
[2] Rozhansky V, Kaveeva E, Senichenkov I, Vekshina E 2018 Plasma Phys. Control. Fusion 60 035001
[3] Meier E T, Goldston R J, Kaveeva E G, Makowski M A, Mordijck S, RozhanskyV A, Senichenkov I Yu,
Voskoboynikov S P 2016 Plasma Phys. Control. Fusion 58 125012
