Erosion of Si- and Ti doped graphites due to deuterium irradiation

Abstract

During irradiation of carbon materials with hydrogen ions hydrocarbon molecules are formed resulting in an enhancement of the erosion yield. At temperatures around 800 K hydrocarbon molecules are released in a thermal activated process, while at low temperatures and low ion energies physical sputtering of lightly bound hydrocarbon radicals enhances the erosion yield. Doping of carbon materials with B, Si and Ti results in a reduction of its chemical reactivity with hydrogen ions. While B reduces drastically the thermal activated process it does not alter the sputtering of hydrocarbons at low energies. For isotropic graphites doped with 10at% Si (LS10) and 10at% Ti(LT10) it is shown that preferential erosion of carbon leads to enrichment of the dopant at the surface. The thermal activated hydrocarbon emission is reduced already at low ion fluences for LS10 and LT10, while the low energy process is only reduced after high fluence irradiation and carbon surface depletion in the case of Ti doping. Depending on the microstructure of the material a very pronounced surface topography delevopes. Carbidic grains protect the underlying carbon material from erosion until a columnar structure evolves. Due to the high threshold for physical sputtering of Ti the total erosion yield for LT10 shows the predicted threshold behaviour for physical sputtering.