Temperature Dependence of Deuterium and Helium Accumulation in W and Ta Coatings during D⁺- or He⁺-Ion Irradiation

Abstract

Thermal desorption spectrometry (TDS) is used to study the processes of the accumulation and thermal release of deuterium and helium in tungsten and tantalum coatings of three-layer composites consisting of a stainless-steel substrate and an intermediate titanium layer, depending on the temperature of the samples upon 20-keV ${\text{D}}_{{\text{2}}}^{ + }$- or He⁺-ion irradiation. The sample temperature range 290–870 K affects the TDS spectra of these gases. With an increase in the sample temperature the deuterium and helium concentrations and capture coefficients decrease in coatings of both types. The mechanisms of deuterium and helium accumulation and thermal desorption as well as the formation of crystal lattice defects are proposed. Deuterium and helium are captured by radiation-induced defects of the vacancy type, forming gas–vacancy complexes. An increase in the sample temperature during ${\text{D}}_{{\text{2}}}^{ + }$- or He⁺-ion irradiation enhances the thermal desorption of implanted gases caused by the dissociation of gas–vacancy complexes, the migration of gas particles through lattice interstices to the surface, and deuterium recombination into a D₂ molecule and its release to free space.