Speaker
Volker Naulin
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.101.pdf
The intermittent SOL: Setting plasma performance and power handling
V. Naulin
DTU Fysik, Plasma Physics and Fusion Energy group, Byg 309, DK 2800 Lyngby
vona@fysik.dtu.dk
The region of open magnetic field lines in tokamaks, which establishes the contact of the confined
plasma with material surfaces, has often only been perceived as a boundary condition to the core plasma,
with the main effect of providing a source of impurities. In the recent years, it has become increasingly
clear that the SOL is setting the conditions for core plasma performance and confinement transitions
between low and high confinement.
Simulations dropping the distinction between fluctuations and background have been highly successful
in reproducing crucial features of the SOL without the input of fitting parameters. Both transitions to H
mode with intermittent access to the H mode have been demonstrated and selected power scalings have
been recovered. More recently the fuelling of fusion plasmas and the influence of the particle source
region in the plasma edge has gained vast attention. Experimental and numerical investigations are
underway to understand the effects of SOL intermittency on fuelling and eventual inward pinch effects
through the pedestal and via the X-point. The statistical properties of the SOL fluctuations are now well
established and can be described as a super-position of uncorrelated pulses from the confinement region
into the SOL domain.
The saturation of the SOL profiles, that is shoulder formation and their potential connection with plasma
detachment and HL back transition, has gained attention as detachment needs to be obtained to mitigate
power loads in any realistic divertor operation regime with stable H-Mode operation.
The theoretical explanation of the observed heat loads to the divertor and first wall elements and their
extrapolation towards ITER conditions is challenging and needs support from accompanying numerical
simulations. Large-scale kinetic simulations give stimulating input, but ultimately systematic scans of
the parameter space in operating tokamaks are mandatory. The inclusion of finite temperature ion
dynamics and neoclassical effects were successful for connecting empirical results to physics
interpretation, revealing the role of zonal flows for the initial access to H mode and reproducing SOL
fall off lengths,
While much progress has been obtained in understanding the non-local and intermittent nature of the
SOL, large gaps in our understanding remain, specifically the interaction with neutrals and plasma facing
components especially divertor regions. Many species plasmas and most certainly geometry effects will
be the areas where most development is expected. We here review recent experimental findings and
contrast them with present simulation results including the effects of neutral turbulence interaction.
