Stress induced hydrogen self-trapping in tungsten*

It has been observed experimentally that hydrogen concentrations as high as ~1 at.% can be retained in surface layer of plasma exposed tungsten samples. However, mechanism of retention of such high amounts of hydrogen is not understood. We present molecular dynamics simulations that demonstrate formation of self-trapped hydrogen platelets in tungsten induced by stresses, in particular, those produced by dislocations. We also show that hydrogen self-trapping in tungsten can occur spontaneously at high hydrogen concentrations ~10 at.%. The platelets are capable to retain large quantities of hydrogen, exceeding trapping capacity of other non-cavity defects in tungsten by orders of magnitude. The formation mechanism and properties of the hydrogen platelets formed in tungsten are described. The hydrogen de-trapping energy from the platelets is also obtained. Based on the simulation findings, we present a model of hydrogen retention via the dislocation-induced self-trapping, which describes retained quantities and dynamics of hydrogen in plasma exposed tungsten.