Hydrogen incorporation into tungsten deposits growing by hydrogen plasma sputtering

Understanding of hydrogen accumulation behavior in tungsten deposits is important from viewpoints of tritium economy and tritium safety in fusion reactors. Some reports indicate that a large amount of hydrogen isotope is incorporated into tungsten deposits growing by hydrogen plasma sputtering. However, the mechanism of hydrogen incorporation is not clarified yet. In this work, tungsten deposits were formed at different circumstances in the sputtering device and the amount of incorporated hydrogen was measured. The implantation of hydrogen reflected from the sputtering target was mainly contributed to the hydrogen incorporation. The contribution of the implantation of reactive hydrogen from plasma was smaller than that of the reflected hydrogen in the experimental condition. A detectable amount of tungsten deposits was formed even in the shadow region from the sputtering target. This suggests that a certain amount of tungsten atoms, which lost its initial energy by collision with molecular hydrogen, diffuses in the gas phase and adheres in the shadow region.