Deuterium retention in tungsten and tungsten–tantalum alloys exposed to high-flux deuterium plasmas

Abstract

A direct comparison of deuterium retention in samples of tungsten and two grades of tungsten-tantalum alloys-W1%Ta and W-5%Ta, exposed to deuterium plasmas (ion flux ∼10 24 m −2 s −1 , ion energy at the biased target ∼50 eV) at the plasma generator Pilot-PSI was performed using thermal desorption spectroscopy (TDS). No systematic difference in terms of total retention in tungsten and tungsten-tantalum was identified. The measured retention value for each grade did not deviate by more than 24% from the value averaged over the three grades exposed to the same conditions. No additional desorption peaks appeared in the TDS spectra of the W-Ta samples as compared with the W target, indicating that no additional kinds of traps are introduced by the alloying of W with Ta. In the course of the experiment the same samples were exposed to the same plasma conditions several times, and it is demonstrated that samples with the history of prior exposures yield an increase in deuterium retention of up to 130% under the investigated conditions compared with the samples that were not exposed before. We consider this as evidence that exposure of the considered materials to ions with energy below the displacement threshold generates additional traps for deuterium. The positions of the release peaks caused by these traps are similar for W and W-Ta, which indicates that the corresponding traps are of the same kind.

Depth profiling of the modification induced by high-flux deuterium plasma in tungsten and tungsten–tantalum alloys

“…On the other hand, in the pre-exposed samples the contribution of the bulk to the total retention is much higher (between 30% and 40%). This difference in bulk retention for the pre-exposed and not pre-exposed samples indicates that the plasma-induced material modification is strong enough to significantly influence the retention, as it was earlier demonstrated by the observation of the history effect of retention due to high-flux D plasma exposure [4]. Moreover, it also clearly indicates that enhancement of retention as a result of high-flux plasma exposure occurs not only in the implantation zone, but at depths down to several micrometres.…”

“…A subsequent TDS run removes the deuterium that was trapped during the damaging exposure from these defects, ideally leaving defects themselves intact. This was shown by earlier observations of the history effect [4] proving that indeed material modifications induced by the high-flux damaging exposure at least partly survive the heat treatment (which includes heating to 1300 K, albeit for a short time of 5 min only) during the TDS measurement. During the probing exposures these defects are again decorated with deuterium.…”

“…It was also demonstrated to be affected by plasma exposure in a manner similar to W, i.e. it features a similar history effect [4].…”

“…Since the assessment of W-Ta as a candidate PFM is in progress [4,[9][10][11][12], we studied the depth distribution of plasma-induced material modification for W-Ta as well.…”

The effect of ion flux on plasma-induced modification and deuterium retention in tungsten and tungsten–tantalum alloys

“…It can manifest itself by the formation of subsurface cavities associated with surface blisters [5], [6], as well as by the generation of atomic defects [7]. Plasma-induced material modification was also found to significantly influence deuterium retention, leading to the emergence of a history effect -the enhancement of the deuterium retention after the pre-exposure to low-energy, high-flux deuterium plasma [8].…”