Dynamic Process of Hydrogen Recycling at First Wall

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In order to investigate hydrogen recycling behavior at first wall of fusion reactor, dynamic process of hydrogen reflection, re-emission and permeation under hydrogen ion and atom bombardments are systematically investigated for various first wall candidate materials. Visible light emission from the target surface under the hydrogen ion bombardment is also analyzed spectroscopically. Employing Ar ion laser, in-situ laser Raman analysis is carried out to monitor damaging process of the irradiated surface.Results obtained are summarized as follows(1) H emission emitted by reflected hydrogen atom from target surface is found to be very useful for understanding hydrogen reflection from graphite and molybdenum.(2) Broad band emission from the surface of metallic target is observed and is attributed to be due to the impurity oxygen on the surface. Strong light emission is observed from ceramics originating from the color centers or impurities of the ceramics. The intensity of the emission quite dependent on the target condition. In the case of graphite target band emission from CH and CH_2 molecules is observed indicating H-C interaction. The present results clearly indicate that the ion induced photon (light) emission is a new technique for investigation of ion-solid interactions.(3) Damaging process of the graphite surface by hydrogen ion bombardment are examined by the in-situ laser Raman spectroscopy, which is very successful giving clear image for amorphizing process of the graphite by hydrogen ion bombardment.(4) Hydrogen reemission, retention and permeation at the first wall candidate materials are investigated using hydrogen molecules, atoms and ions and the effect of energy deposition of ion bombardment on hydrogen recycling is analyzed comparing the three cases.