  We carry out generalized-ensemble molecular dynamics simulations of the
formation of small Helium (He) clusters in bulk Tungsten (W), a process of
practical relevance for fusion energy production. We calculate formation free
energies of small Helium clusters at temperatures up to the melting point of W,
encompassing the whole range of interest for fusion-energy production. From
this, parameters like cluster break-up or formation rates can be calculated,
which help to refine models of microstructure evolution in He-irradiated
Tungsten.
