Behaviour of Reversible Hydrogen Getters under the Pulsed Plasma Heat Loads

I. Garkusha (Sp), O.V. Byrka, V.I. Tereshin, A.V. Tsarenko, NSC KIPT, Kharkov (Ukraine); J. Baranowski, M.J. Sadowski, E. Skladnik-Sadowska, The Andrzej Soltan Institute for Nuclear Studies, Swierk (Poland); V.N. Borisko, Kharkov National University (Ukraine) 
Features of pulsed plasma streams interaction with metal-hydrides, made on the basis of ZrVFe alloys, in conditions of high-heat load and intensive recycling of previously accumulated hydrogen are discussed. It was found that hydrogen desorption contributes to considerable decreasing both the energy density value delivered to the material surface and metal-hydride erosion due to quick formation of protective gas target near the material surface. Such effect can be useful for protection of plasma facing components and elements of diagnostics in zones of intensive heat release. For fusion applications the high erosion- and thermal stability as well as the possibility of easy desorption of tritium are important.
Hydrogen spectra in plasma shield were studied with MECHELE-900 optical spectrometer. Plasma density close to the sample surface obtained from Stark broadening of hydrogen lines achieved 5x1016 cm-3. Lines of getter components were also analyzed. Duration of plasma shield existence obtained from optical measurements essentially exceeded both time of plasma stream exposure and plasma shield duration for irradiation of metal targets. Comparative analysis of shielding layer parameters for nitrogen and hydrogen plasma irradiation has been performed.
Thermal desorption analysis of the targets before and after the plasma irradiation has been performed. Dependence of desorption peaks on initial level of saturation by hydrogen was found. Hydrogen sorption of non-saturated getter under hydrogen plasma stream irradiation was investigated also. The contributions of two competitive processes, e.g. the hydrogen doping by plasma stream during the interaction with the target and desorption of hydrogen, have been discussed.
XRD shows formation of intermetallic phase of ZrCu5 and modification of surface layer as result of plasma irradiation. Modified layer with depth of several micrometers has a fine-crystalline or apparently amorphous-like structure. Influence of plasma exposures on pores distribution in getter material is analyzed also.

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