The calculation of the dissociation of hydrogen from helium clusters in tungsten

Abstract

The synergistic effects of H and He interactions in W are important issues in the development of nuclear fusion devices. In this work, a series of molecular static and molecular dynamic (MD) simulations were conducted to investigate the H dissociation from interstitial HemH clusters. The molecular static simulations show that Hem clusters and HemH clusters have several energy states at 0 K, suggesting the complexity of the dissociation process where various dissociation paths with differing energy barriers exist. Thus, in the molecular dynamics phase, we propose a linearly increasing temperature technique that is an emulation of thermal desorption experiments to calculate the coarse-grained dissociation rate of H atoms from HemH clusters. Despite the complexity of the H dissociation process, our results showed that a single coarse-grained activation energy Ea can be extracted to characterise the complicated process that can be considered a thermal activated event based on our theory. To demonstrate the application of the results, we calculated and compared the H dissociation rate and the rate for Hem clusters colliding with H atoms. The comparison at 500 K shows that the rate for the Hem clusters colliding with the H atoms is much faster than H atoms dissociating from HemH clusters, suggesting that HemH clusters at this temperature should be used in some long-term models. The proposed method can also be extended to calculate the coarse-grained rate coefficients of other types of clusters.