Collisional transport of impurities with flux-surface varying density in stellarators

Abstract

High-Z impurities in magnetic confinement devices are prone to develop density variations on the flux-surface, which can significantly affect their transport. In this paper, we generalize earlier analytic stellarator calculations of the neoclassical radial impurity flux in the mixed-collisionality regime (collisional impurity and low-collisionality bulk ions) to include the effect of such flux-surface variations. We find that only in the homogeneous density case is the transport of highly collisional impurities (in the Pfirsch-Schlüter regime) independent of the radial electric field. We study these effects for a Wendelstein 7-X (W7-X) vacuum field, with simple analytic models for the potential perturbation, under the assumption that the impurity density is given by a Boltzmann response to a perturbed potential. In the W7-X case studied, we find that larger amplitude potential perturbations cause the radial electric field to dominate the transport of the impurities. In addition, we find that classical impurity transport can be larger than the neoclassical transport in W7-X.

arXiv comment20 pages, 5 figures

References in corpus (5)

• Impurity transport in a mixed-collisionality stellarator plasma
• Stellarator impurity flux driven by electric fields tangent to magnetic surfaces
• Impurity transport and bulk ion flow in a mixed collisionality stellarator plasma
• Stellarator bootstrap current and plasma flow velocity at low collisionality
• Impurity transport in Alcator C-Mod in the presence of poloidal density variation induced by ion cyclotron resonance heating

Cited by in corpus (11)

• KNOSOS: a fast orbit-averaging neoclassical code for stellarator geometry
• Turbulent impurity transport simulations in Wendelstein 7-X plasmas
• Stellarator impurity flux driven by electric fields tangent to magnetic surfaces
• Turbulent transport of impurities in 3D devices
• Study on impurity hole plasmas by global neoclassical simulation
• Impact of main ion pressure anisotropy on stellarator impurity transport
• The importance of the classical channel in the impurity transport of optimized stellarators
• Impurity temperature screening in stellarators close to quasisymmetry
• Electron root optimisation for stellarator reactor designs
• Direct optimization of neoclassical ion transport in stellarator reactors
• Optimization of flux-surface density variation in stellarator plasmas with respect to the transport of collisional impurities