DEUTERIUM PERMEATION THROUGH NB DURING LOW-ENERGY ION IRRADIATION AT CONTROLLED SURFACE CONDITIONS

Permeation rates of deuterium through a niobium membrane have been inv estigated as a function of the primary ion energy and the membrane tem perature at controlled surface conditions. A mass separated ion beam w ith the ion energy in the range of 400-1500 eV per deuteron was used. The ion channel supplied a high ratio of the ion beam current to the b ackground molecular flux to the surface. It allowed to measure the flu xes of reflected and reemitted particles along with the permeation flu x with in-situ surface analysis by Auger electron spectrometry (AES) a nd secondary ion mass spectrometry (SIMS). The recombination rate coef ficients were obtained experimentally in steady-state conditions for b oth upstream-side and downstream-side membrane surfaces by evaluating the concentration of dissolved hydrogen by means of thermodesorption t echnique and taking into account the contribution of the reflected par ticles to the flux balance. Experimental data of the hydrogen recombin ation coefficient have been compared with the numerical evaluation by using the Richards-Nagasaki model.