Fusion Science and Technology / Volume 38 / Number 3 / November 2000 / Pages 357-362
Technical Paper / Special Issue on Beryllium Technology for Fusion
The mixed W-Be layers were prepared by deposition of Be and W atoms on a Be substrate under simultaneous sputtering of Be and W targets by 20 keV Ar+-ions. The thickness of the deposited mixed W-Be layer was ∼500 nm. The element composition analysis of these layers showed that the mixed layer contains up to 35 at.% W, up to 35 at.% Be and up to 30 at.% O. The W-Be films on Be were irradiated by pulsed deuterium plasma flux in the electrodynamic plasma MKT-accelerator with a deuterium plasma concentration of 1021 m−3, maximal ion energy of (1–2) keV and with the energy flux density of 0.2 MJ/m2 per pulse. The pulse duration was equal to 60 μs. After irradiation by two plasma pulses the W-Be film is melted and removed completely from the local surface areas. The element distributions in a mixed layer after an effect of the pulsed plasma are essentially changed. For the surface areas with the removed film the Be concentration is about 75 at.%, W — about 15 at.%, O - about 10 at.% and the penetration of W and O atoms is up to 1000 nm deep of Be substrate. For the surface areas with the retained melted film the Be surface concentration increase up to 90 at.%, tungsten and oxygen concentration decrease about 2–3 times. The method of Elastic Recoil Detection Analysis was used to study D retention. The integral deuterium concentrations are equal to 0.6·1020 and 2.2·1020 m−2 for the removed film areas and for the retained melted film ones, correspondingly. Consequently, deposited W-Be film promotes the essential reduction of D retention in Be substrate. Transmission electron microscopy was used to study the erosion product size distribution. The erosion products were collected on basalt filter fibers located in a shadow of the pulsed plasma flux around the exposed WBe film target. The erosion product size distribution has two maxima located in the ranges 0.1–0.2 μm and 2.5–5.0 μm.