Speaker
Description
See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I3.102.pdf
Two of the highest priorities in stellarator research are to verify the effects of orbit driftoptimization on the energy core confinement and to learn to prevent the accumulation of impurities in high-density plasmas. The basic framework for understanding energy and particle transport in these devices is neoclassical theory and plasma flows is one of its most fundamental predictions, upon which further transport modeling relies.
In this talk we will present an integral interpretation of flow measurements, in terms of the neoclassical ambipolar radial electric field and the Pfirsch-Schl¸ter and net parallel velocities, to test our understanding of plasma flows in high-density, low-collisionality (i.e. optimization relevant) plasmas. Furthermore, the deviation of impurity flow fields from an incompressible spatial variation has been linked to significant inhomogeneities of impurity density on flux surfaces (see e.g. [1] and references), which, in turn, give rise to a damped low-frequency oscillation in the radiation traces after sudden profile changes such as those caused by pellet injections [1]. The observation of a similar oscillation in W7-X plasmas [2] has sparked the question whether such impurity density variations can also be observed in W7-X and whether or not they are important in determining the radial impurity fluxes. In the talk, fluid and kinetic modeling of the density variation and radial fluxes will be presented and confronted with the observed X-ray oscillations as well as with the stationary radial fluxes calculated with the three-charge-states technique [3] to provide an up-to-date status of our understanding of these questions.
[1] J A Alonso, J L Velasco, I Calvo et al. 2016 Plasmas Phys. Control. Fus. 58 074009.
[2] C. Brandt, H. Thomsen, T. Andreeva et al. 2018 EPS Plasma Phys. Conference, P4.1056.
[3] A. Langenberg, N. Pablant, O. Marchuk et al. 2017 Nucl. Fusion 57 086013.
