Gyrokinetic modelling of impurity peaking in JET H-mode plasmas

Gyrokinetic modelling of impurity peaking in JET H-mode plasmas

Gyrokinetic modelling of impurity peaking in JET H-mode plasmas 150 150 Mathew
CCFE-PR(17)42

Gyrokinetic modelling of impurity peaking in JET H-mode plasmas

Quantitative comparisons are presented between gyrokinetic simulations and experimental values of the carbon impurity peaking factor in a database of JET H-modes during the carbon wall era. These plasmas feature strong NBI heating, hence high values of toroidal rotation and correponding gradient. Furthermore, the carbon profiles present particularly interesting shapes for fusion devices, i.e. hollow in the core and peaked near the edge. Dependencies of the experimental carbon peaking factor (R=LnC ) on plasma parameters are investigated via multilinear regressions. A marked correlation between R=LnC and the normalised toroidal rotation gradient is observed in the core, which suggests an important role of the rotation in establishing hollow carbon profiles. The carbon peaking factor is then computed with the gyrokinetic code GKW, using a quasi-linear approach, supported by few non-linear simulations. The comparison of the quasi-linear predictions to the experimental values at mid-radius reveals two main regimes. At low normalised collisionality, v*, and Te=Ti < 1 the gyrokinetic simulations quantitatively recover experimental carbon density profiles, provided roto-diffusion is taken into account. In contrast, at higher v* and Te=Ti > 1, the very hollow experimental carbon density profiles are never predicted by the simulations and the carbon density peaking is systematically over estimated. This points at a possible missing ingredient in this regime.

Collection:
Journals
Journal:
Physics of Plasmas
Publisher:
AIP
Published date:
06/01/2017