Abstract Details
Abstracts
Author: Julien Dominski
Requested Type: Pre-Selected Invited
Submitted: 2019-02-22 19:42:05
Co-authors: C.S. Chang, R.M. Churchill, R. Hager, P. Helander, S. Ku, E.S. Yoon
Contact Info:
Princeton Plasma Physics Laboratory
100 Stellarator rd
Princeton, New Jersey 08540
USA
Abstract Text:
The formation of large amplitude up-down asymmetries that invalidate the use of the small neoclassical ordering (f=f0+epsilon f1 with epsilon=rho/a) are observed in XGCa neoclassical gyrokinetic simulations, including full-f non-Maxwellian multi-species collisions [Hager et al., Journal of Computational Physics, 315 (2016)]. These up-down asymmetries are observed to be large for heavy impurities with high electric charge (Z>10). Estimates of the neoclassical impurity fluxes based on this small ordering are thus found to be inaccurate, as they miss the effect of strong poloidal asymmetric density [Angioni and Helander, Plasma Physics and Controlled Fusion, 56 (2014)]. They are off by up to 30% for tungsten with Z=40. This study is conducted for a circular test case with tight aspect ratio, and mild density and temperature gradients. A study is also conducted for a realistic H-mode plasma with magnetic separatrix. The main ions are in the banana collision regime and the impurities are in the Pfirsch-Schluter collision regime. The influence of the parallel electric field and parallel friction force, which are assumed to dominate over the parallel viscosity [Helander, Phys. Plasmas, 5 (1998)], will be discussed. The validity of the Maxwellian approximation for impurities will also be discussed. Verification of XGCa against analytic predictions and simulations with the NEO code [Belli et al., Plasma Physics and Controlled Fusion 54 (2012)] are successfully carried out in regimes where the small ordering is valid. Formation of large amplitude asymmetries in geometry including X-point and pedestal will also be discussed.
Comments:
1/ Computer Simulation of Plasmas
2/ Plasma Properties, Equilibrium, Stability, and Transport
3/ Physics of Plasma Edge and Divertor Region
4/ Plasma Production and Heating
