Predicting helium retention in tungsten is of relevance for future nuclear fusion reactors as it influences tritium uptake and transport, the latter effects being a critical question to achieve tritium self-sufficiency.
While the macroscopic effects of helium agglomeration in tungsten are known it is still an open topic of discussion what the underlying processes on a microscopic scale are. Our goal is to contribute to this discussion by providing experimental results for "simple", i.e only containing vacancy defects, tungsten systems.
We therefore compare samples where defects have been induced by either self-ion bombardment (MeV range), MeV electron bombardment or thermal quenching. While the samples' initial state and post damaging state are also monitored by different types of microscopy, Doppler-broadening spectroscopy is used as the main tool since it shows the highest sensitivity to vacancy-like defects. The positron-annihilation measurements shown have all been performed on a tungsten-moderated, Na-22-based mono-energetic slow positron beam at FRM II which has been modified to deliver acceleration voltages of up to 40 kV.