Abstract
One of the key problems for the application of nuclear fusion energy is to select the suitable plasma facing materials (PFMs). Among the W-based materials, CVD-W exhibits some unique advantages. In order to estimate the performance of CVD-W under the fusion environment, the vacancy-type defects and their evolution are investigated by the Doppler-broadening slow positron beam analysis (DB-SPBA) combined with SEM (scanning electron microscope). There are two kinds of neutral beam irradiation, the pure H neutral beam and the H + 6 at.% He neutral beam irradiation, which are performed at the neutral beam facility GLADIS (IPP, Germany). The surface temperatures of CVD-W irradiated by H (H + 6 at.% He) are 850 and 1000 (700 and 800 °C). By comparing the samples under different conditions, the defect evolution of CVD-W is obtained. As for the pure H neutral beam irradiated samples, the DB-SPBA results demonstrate that the CVD-W sample at the surface temperature of 1000 °C, compared to the 850 °C sample, shows a decrease in S parameters, which is due to the reduction of vacancy-type defect concentration. The defect damage layer in 1000 °C sample is narrower than that of 850 °C sample and the defect type tends to be consistent in 1000 °C sample. The SEM results suggest that the surface damage of the 1000 °C sample was recovered to some extent. As for the H + 6 at.% He neutral beam irradiated samples, compared with the CVD-W sample at the surface temperature of 700 °C, the 800 °C sample shows an increased S parameters, which can be attributed to the volume increase of vacancy-type defect. The defect damage layer in the 800 °C sample is wider than that of the 700 °C sample. Both the H + 6 at.% He irradiated samples show complex defect types. The surface of the 800 °C sample exhibits more dense pinhole damage structures compared to that of the 700 °C sample.
Highlights
Nuclear fusion energy has been widely concerned and highly valued for its safe, clean, and environment-friendly traits
In the operation of fusion reactor, the plasma-facing materials (PFMs) are subjected to extremely severe conditions: the high flux plasma particle bombardment, high energy neutron irradiation, steady-state thermal shock, and transient thermal shock [1,4]
The study is of great significance to understand the resistance of chemical vapor deposition (CVD)-W samples to the H/He neutral beam irradiation and it provides valuable help to estimate the actual applications of CVD-W
Summary
Nuclear fusion energy has been widely concerned and highly valued for its safe, clean, and environment-friendly traits. In the operation of fusion reactor, the PFMs are subjected to extremely severe conditions: the high flux plasma particle bombardment, high energy neutron irradiation, steady-state thermal shock, and transient thermal shock [1,4]. The divertor materials will be exposed to the H (D or T)/He mixed plasma with the flux of 1024 –1028 m−2 ·s−1. He is mainly produced by D-T reaction and its concentration in burning plasma can be 5–10% (atomic fraction) [26,27]. The study is of great significance to understand the resistance of CVD-W samples to the H/He neutral beam irradiation and it provides valuable help to estimate the actual applications of CVD-W in fusion reactors
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