On helium cluster dynamics in tungsten plasma facing components of fusion devices

摘要

This paper describes the dynamics of helium clustering behaviour within either a nanometer-sized tendril of fuzz, or a half-space domain, as predicted by a reaction-diffusion model. This analysis has identified a dimensionless parameter, P_Δ, which is a balance of the reaction and diffusion actions of insoluble He in a metal matrix and which governs the self-trapping effects of He into growing bubbles within a tendril. The impact of He self-trapping, as well as trapping caused by pre-existing traps in the form of lattice defects or clusters of impurities, within a half-space domain results in the formation of a densely packed layer of nanometer-sized bubbles with high number density. This prediction is consistent with available experimental observations in which a dense zone of helium bubbles is observed in tungsten, which are compared to estimates of the layer characteristics. Direct numerical simulation of the reaction-diffusion cluster dynamics supports the analysis presented here.