REDUCTION OF THE CHEMICAL EROSION OF DOPED GRAPHITE DUE TO SURFACE MODIFICATION DURING LOW-ENERGY D+ BOMBARDMENT

The chemical erosion yield of pure graphite during hydrogen bombardmen t is strongly reduced by dopants like Ti, Si, or B. Preferential sputt ering and changes of the surface composition as well as influences of the dopant-carbon bonding on methane formation consequently change the erosion yield. Surface changes may be accentuated:lt low energy hydro gen ion bombardment and elevated temperatures. The changes of the surf ace compositions of titanium doped graphites and of pure TiC during bo mbardment with D+ ions below an ion energy of 1 keV and temperatures u p to 1000 K was investigated. Ti concentrations up to 75 at% at room t emperature and stoichiometric TiC concentrations at enhanced temperatu res were found. Qualitative investigations of the Auger carbon signal fine structure confirms the phase changes. Due to these changes in mat erial composition the chemical erosion yield is suppressed and the ero sion dominated by physical sputtering.