On collisional impurity transport in nonaxisymmetric plasmas

Joint Varenna-Lausanne International Workshop 2014

Mollén, A.^1 ; Landreman, M.^2 ; Smith, H.M.^3

Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden^1

Institute for Research in Electronics and Applied Physics, University of Maryland, College Park

MD

20742, United States^2

Max-Planck-Institut fur Plasmaphysik, Greifswald

17491, Germany^3

关键词: Ambipolar radial electric fields;    Bootstrap current;    Effective charge;    Impurity accumulations;    Impurity transport;    Magnetic confinement fusions;    Magnetic geometry;    Stellarator plasma;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/561/1/012012/pdf
DOI  :  10.1088/1742-6596/561/1/012012

来源: IOP

【 摘 要 】

The presence of impurity species in magnetic confinement fusion devices leads to radiation losses and plasma dilution. Thus it is important to analyze impurity dynamics, and search for means to control them. In stellarator plasmas the neoclassical ambipolar radial electric field often points radially inwards (referred to as the ion root regime), causing impurities to accumulate in the core. This can limit the performance of nonaxisymmetric devices. In the present work we analyze neoclassical impurity transport in stellarator plasmas using a recently developed continuum drift-kinetic solver, the SFINCS code (the Stellarator Fokker- Planck Iterative Neoclassical Conservative Solver). The study is performed for a case close to the edge of W7-X using the standard configuration magnetic geometry. We investigate the sensitivity of impurity transport to impurity charge, main species density and temperature gradients, as well as ion temperature. At the studied radial location we find that the neoclassical impurity peaking factor can be very large, particularly for high-Z impurities. The ambipolar radial electric field is in the ion root regime, and impurity accumulation can thus be expected. The accumulation is strengthened by the large main species density and temperature gradients. Moreover we find that the size of the bootstrap current is affected by the value of the plasma effective charge, suggesting that employing a realistic ion composition can be important when calculating the bootstrap current.