In situ deuterium observation in deuterium-implanted tungsten

Abstract

In order to evaluate the tritium inventory in plasma-facing tungsten components of a fusion reactor, deuterium depth profiles in tungsten were observed in situ using nuclear reaction analysis (NRA) under continuous implantation of 3keV D ions. Measurements were conducted at temperatures of 384, 473, 573 and 673K. Recombination coefficients and rate constants for the surface recombination process were estimated from the observed deuterium concentration. It is indicated that the measured surface recombination rate constant is applied in a case wherein tungsten is exposed to hydrogen particles of various energies from a fusion plasma. The measured recombination coefficient was identical to that found by a different technique in a previous work. Deuterium in trap sites was found to contribute to deuterium retention in the samples as well as to deuterium in solution sites. The deuterium retention was low in the 384K sample, in which trap sites had not appeared. Deuterium retention was very low in the 673K sample, where most deuterium atoms were detrapped and desorbed. At an intermediate temperature of 473K, the retention showed a maximum value due to a large occupancy of deuterium over many trap sites. The dependence of the retention on deuterium fluence was explained assuming that trap sites were produced by implantation.