Incident Ion Energy and Temperature Dependence of Helium Bubble Formation and Its Impact on D-Retention Under Simultaneous He-D Irradiation of Tungsten

The structure and concentration distribution of He, H, and D in the ion implanted zone following simultaneous He-D irradiation in W was characterized. A shift in He bubble size from nanometer to tens of nanometers was observed between 800 K < T < 1000 K. The bubble field was found to extend to depths of 30-40 nm with mean concentrations of 4-5 at.%.. An order of magnitude increase in He trapping was observed at 800 K when the ion energy was increased from 0.3 to 1.0 keV. Depth profiles of the trapped D at 500 K indicatea marked decrease in the trapped amount coinciding with the He bubble layer. Conversely, enrichment in hydrogen concentration was observed. One hydrogen atom was found to trap in ratio with ~6 He atoms. Such preferential trapping of hydrogen appears to be an important process in the reduction of D diffusion into W due to He effects.