Moderation of neoclassical impurity accumulation in high temperature plasmas of helical devices

Abstract

Achieving impurity and helium ash control is a crucial issue in the path towards fusion-grade magnetic confinement devices, and this is particularly the case of helical reactors, whose low-collisionality ion-root operation scenarios usually display a negative radial electric field which is expected to cause inwards impurity pinch. In these work we discuss, based on experimental measurements and standard predictions of neoclassical theory, how plasmas of very low ion collisionality, similar to those observed in the impurity hole of the Large Helical Device, can be an exception to this general rule, and how a negative radial electric field can coexist with an outward impurity flux. This interpretation is supported by comparison with documented discharges available in the International Stellarator-Heliotron Profile Database, and it can be extrapolated to show that achievement of high ion temperature in the core of helical devices is not fundamentally incompatible with low core impurity content.

References in corpus (9)

• Comparison of particle trajectories and collision operators for collisional transport in nonaxisymmetric plasmas
• The effect of tangential drifts on neoclassical transport in stellarators close to omnigeneity
• On neoclassical impurity transport in stellarator geometry
• Calculation of the bootstrap current profile for the TJ-II stellarator
• Study of the neoclassical radial electric field of the TJ-II flexible heliac
• Particle transport after pellet injection in the TJ-II stellarator
• Damping of radial electric field fluctuations in the TJ-II stellarator
• Compressible impurity flow in the TJ-II stellarator
• Parallel impurity dynamics in the TJ-II stellarator

Cited by in corpus (12)

• 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
• Robust stellarator optimization via flat mirror magnetic fields
• Quasilinear particle transport from gyrokinetic instabilities in general magnetic geometry
• Study on impurity hole plasmas by global neoclassical simulation
• 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
• Effects of collisions on impurity transport driven by electrostatic modes