Impurity transport in a mixed-collisionality stellarator plasma

Abstract

A potential threat to the performance of magnetically confined fusion plasmas is the problem of impurity accumulation, which causes the concentration of highly charged impurity ions to rise uncontrollably in the center of the plasma and spoil the energy confinement by excessive radiation. It has long been thought that the collisional transport of impurities in stellarators always leads to such accumulation (if the electric field points inwards, which is usually the case), whereas tokamaks, being axisymmetric, can benefit from "temperature screening", i.e., an outward flux of impurities driven by the temperature gradient. Here it is shown, using analytical techniques supported by results from a new numerical code, that such screening can arise in stellarator plasmas too, and indeed does so in one of the most relevant operating regimes, where the impurities are highly collisional whilst the bulk plasma is in any of the low-collisionality regimes.

11 pages, 3 figures

References in corpus (2)

• Comparison of particle trajectories and collision operators for collisional transport in nonaxisymmetric plasmas
• Impurities in a non-axisymmetric plasma: transport and effect on bootstrap current

Cited by in corpus (25)

• Turbulent impurity transport simulations in Wendelstein 7-X plasmas
• Stellarator impurity flux driven by electric fields tangent to magnetic surfaces
• Electrostatic potential variations on stellarator magnetic surfaces in low collisionality regimes
• Impurity transport and bulk ion flow in a mixed collisionality stellarator plasma
• Collisional transport of impurities with flux-surface varying density in stellarators
• Large tangential electric fields in plasmas close to temperature screening
• Strategies for Advantageous Differential Transport of Ions in Magnetic Fusion Devices
• Quasilinear particle transport from gyrokinetic instabilities in general magnetic geometry
• Improved linearized model collision operator for the highly collisional regime
• On-surface potential and radial electric field variations in electron root stellarator plasmas
• Study on impurity hole plasmas by global neoclassical simulation
• MITNS: Multiple-Ion Transport Numerical Solver for Magnetized Plasmas
• Maximum-Entropy States for Magnetized Ion Transport
• Heat Pump via Charge Incompressibility in a Collisional Magnetized Multi-Ion Plasma
• 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
• Generalized Impurity Pinch in Partially Magnetized Multi-Ion Plasma
• Trace Impurity Transport in Multi-Species Plasmas with Large Particle Fluxes
• In-Out impurity density asymmetry due to the Coriolis force in a rotating tokamak plasma
• Electron root optimisation for stellarator reactor designs
• Temperature Screening and Cross-Field Impurity Accumulation from a Thermodynamic Perspective
• Direct optimization of neoclassical ion transport in stellarator reactors
• Effects of collisions on impurity transport driven by electrostatic modes
• Optimization of flux-surface density variation in stellarator plasmas with respect to the transport of collisional impurities