Deuterium retention in codeposited layers and carbon materials exposed to high flux D-plasma

A ceramic BCN target with samples of dense RG-Ti-91 without boron, RG-Ti-B with boron (0.1 at,%) and porous POGO AXF-5Q graphites was exposed in a stationary D-plasma of the 'Lenta' device with an ion energy of 200 eV and an ion flux of (3 - 6) x 10(17) D/cm(2)s at 1040 and 1400 K to a fluence of similar to 1 x 10(22) D/cm(2), Codeposited layers were obtained for comparison on the target surface. Thermal desorption spectroscopy (TDS showed that the amount of deuterium in RG-Ti after exposure at 1040 K was more than an order of magnitude higher than in POGO (9 x 10(17) and 7 x 10(16) D/cm(2), respectively). The retention took place preferentially in a surface layer about 100 mu m thick. The bulk deuterium concentration in both RG-Ti and POGO was lower than 1 appm. The irradiated RG-Ti surface was subjected to strong erosion and consisted of 'columnar' grains covered with TiC at their tips. The deuterium in RG-Ti irradiated at 1400 K was located in the surface layer (1.5 x 10(16) D/cm(2)), The value of the bulk concentration did not exceed 0.1 appm while in POGO it was equal to about 20 appm. TDS for deuterium in RG-Ti demonstrated a spectrum similar to that for codeposited layers on a target surface. The differences in deuterium retention in the graphites are explained on the basis of structural differences. Considering tritium inventory assessment for ITER, dense graphites like RG-Ti are preferred for working divertor plates at high temperatures. (C) 1999 Elsevier Science B.V. All rights reserved.