Speaker
Description
We present large scale molecular dynamics simulations of medium and high velocity W dust particle (10 - 40 nm diameter) impacts on fuzz covered W surfaces, as will likely occur in future fusion energy reactors. Results show that the commonly held intuition, that fuzz structures are fragile, is wrong. Nanorods are ductile due to their small dimensions and they undergo extensive plastic deformation under impact of medium velocity dust particles. A fuzz layer absorbs the energy and momentum of medium velocity small dust particles more gradually over a much greater thickness (up to several hundred nm) and a much longer time scale (up to over 1 ns) than a solid W surface. Impacts of high velocity dust particles do not cause extensive plastic deformation. Instead, dust particles liquefy on first impact on a nanorod, along with part of the nanorod. If the radius of the high velocity dust particle is large enough, the particle will smash through the nanorod, fragment into many smaller liquid droplets and these continue to move deeper into the fuzz layer. The amount of W that reflects back to the vacuum from a high velocity particle impact, as potential high-Z fusion plasma pollutant, ranges from 1/100th to 1/10th of the volume of the dust particle. High velocity particles also lose their energy and momentum over a much greater depth (hundreds of nm) and over a much longer time (hundreds of ps) than on a solid W surface. From a fusion energy application point of view, the results are encouraging, as they show that W fuzz is not fragile but is instead a better absorber for small W dust particles than a W solid surface.