Molecular dynamics simulations of the effect of deuterium on tungsten erosion by oxygen

Chemical erosion of tungsten is one of the critical issues for its use as tokamak armor material. Oxygen impurities in the SOL plasma may deteriorate the good tungsten performance. The regime at the divertor surface heated up to 1500 K is investigated, with SOL particles arriving with energies below the sputtering threshold. Oxygen can form the molecules WO2 and WO3 under deuteron bombardment. The tungsten erosion is assumed due to the sublimation of the WO3 molecules. To calculate this process the classical atomic dynamics analysis code (CADAC) is developed. As a new numerical method, time step clusters are introduced which allow significant acceleration of the calculations, especially for assemblies of atoms of large mass ratios, keeping the conservation of momentum and energy. First results are presented based on a solution of simplified equations for molecular surface densities, with kinetic coefficients obtained by CADAC. The deuteron bombardment significantly reduces the erosion because it destroys the WO2 molecules and removes oxygen due to oxygen sputtering.