An Overview of Recent Standard and Accelerated Molecular Dynamics Simulations of Helium Behavior in Tungsten.

Luis Sandoval,Danny Perez,Blas P. Uberuaga,Arthur F. Voter

doi:10.3390/ma12162500

Abstract

One of the most critical challenges for the successful adoption of nuclear fusion power corresponds to plasma-facing materials. Due to its favorable properties in this context (low sputtering yield, high thermal conductivity, high melting point, among others), tungsten is a leading candidate material. Nevertheless, tungsten is affected by the plasma and fusion byproducts. Irradiation by helium nuclei, in particular, strongly modifies the surface structure by a synergy of processes, whose origin is the nucleation and growth of helium bubbles. In this review, we present recent advances in the understanding of helium effects in tungsten from a simulational approach based on accelerated molecular dynamics, which emphasizes the use of realistic parameters, as are expected in experimental and operational fusion power conditions.

Highlights

Conditions expected in the divertor of the world’s largest tokamak under construction, ITER (“The Way” in Latin, formerly known as International Thermonuclear Experimental Reactor), include the low-energy (≤100 eV) helium nuclei impact on a high-temperature tungsten surface (∼1000 K) [1]
We mostly focus on work from our own group where so-called Accelerated MD (AMD) techniques have been applied to the problem
The results presented provide a comprehensive characterization of the kinetics of small interstitial He clusters in bulk W

Summary

Introduction

Conditions expected in the divertor of the world’s largest tokamak under construction, ITER (“The Way” in Latin, formerly known as International Thermonuclear Experimental Reactor), include the low-energy (≤100 eV) helium nuclei impact on a high-temperature tungsten surface (∼1000 K) [1]. No tungsten defects are created upon impact because the maximum energy transferable from the collision is significantly below the tungsten displacement threshold [2]. The helium atoms diffuse in the tungsten matrix, eventually forming helium clusters with lower diffusion rates. Time scales) entity, composed of the helium cluster and a tungsten Frenkel pair [3]. This helium (nano-)bubble is able to collect additional helium clusters, triggering the nucleation of additional. The bubble grows and the tungsten interstitials form a dislocation line pinned to the bubble, which eventually detaches as a loop, effectively displacing tungsten atoms in the matrix [4,5,6]

Methods

Discussion

Conclusion