Tungsten nanostructure growth by sputtering and redeposition in BCA-MD-KMC hybrid simulation

Abstract

The formation mechanism of fibrous tungsten nanostructures, fuzz, induced by helium plasma irradiation on tungsten materials has been investigated. We have developed a BCA-MD-KMC hybrid simulation, which solves the injection process of helium atoms by the Binary Collision Approximation (BCA) method, the diffusion process of helium atoms in tungsten materials by the Kinetic Monte-Carlo (KMC) method, and the deformation of tungsten materials due to helium bubbles by the Molecular Dynamics (MD) method. In addition, the model used to calculate the recoiling of tungsten atoms in BCA was improved to account for the reduced binding energy of tungsten atoms on rough surfaces. Using the hybrid simulation, the height of the nanostructures reached about 50 nm. The main mechanism of nanostructure growth was that sputtering and redeposition caused transport of tungsten atoms perpendicular to the surface. The present simulation was able to represent not only the dependence that the nanostructure height increases in proportion to the square root of the helium fluence, but also the existence of incubation fluence before the growth starts.

Focus on plasma-facing materials in nuclear fusion reactors

“…While the materials science community has a long history of conducting fundamental and applied research on plasma-materials interactions [6][7][8], this collection focuses on the same type of physics with respect to a nuclear fusion environment. The topics covered are unique to 'Plasma-Facing Materials in Nuclear Fusion Reactors' such as: deuterium and tritium retention in PFCs [9][10][11][12][13]; fundamental processes at the plasma-surface interface [10,[14][15][16][17][18][19][20]; evolution of structure and properties under fusion-reactor-relevant heat loads [21]; material degradation under ion exposure [15,16,19]; material degradation under neutron irradiation [9,21]; material erosion, migration, and deposition [14,15,18,20,22]; plasma fueling [12]; and diagnostics for plasmamaterials interactions [23]. Although the details of the underlying mechanisms that govern the above phenomena remain largely unresolved, the results presented here will drive the emergence of engineering solutions to the amelioration of plasma-facing materials degradation.…”