(IT/P1-17) Methane Formation under Charcoal Interaction with Atomic Hydrogen and Deuterium at 77 K

A.E. Gorodetsky1), S. P. Vnukov1), R. Kh. Zalavutdinov1), V. L. Bukhovetz1), A. P. Zakharov1), Chr. Day2), G. Federici3)
1) Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow, Russian Federation
2) Institut für Technische Physik, Forschungszentrum Karlsruhe, Germany, Po Box 3640, 76021 Karlsruhe, Germany
3) ITER Garching Joint Work Site, Garching, Boltzmannstr. 2, 85748 Garching, Germany

Abstract.  Charcoal is a working material of sorption cryopumps in the ITER project. An interaction of thermal hydrogen (deuterium) atoms and molecules with charcoal has been analyzed by adsorption measurements at 77 K and TDS (77-300 K). A stream quartz tube of 100 cm length, 1 cm radius with an H2(D2)/CH4 RF discharge was used for the production of H(D) atoms and CH3 radicals. The charcoal was an effective sink for atomic hydrogen. Under charcoal interaction with the H(D)/H2(D2) mixture (77 K) the methane or deuteromethane (CD4) appeared in thermodesorption spectrum. Only methane was recorded in mass spectrum at annealing of sample up to 300 K. Methane was observed after a critical fluence depending on charcoal mass. The numbers of methane molecules formed and hydrogen atoms in the tube cross-section with the samples were close to each other. It means that the sticking coefficient of atomic hydrogen for the charcoal surface is close to unity at 77 K. At constant H/H2 flow the methane formation rate was higher for the samples with lesser mass. The methane yield increased with the exposure time. The CD4 yield some exceeded of CH4 one. After increasing temperature (up to 300 K) of the samples exposed in H(D)/H2(D2) mixture remained hydrogenated. Charcoal contained the chemically bound hydrogen in quantities of tenths parts of H atoms fluence. After transfer of the sample to adsorption setup the decreasing of hydrogen sorption capacity (T=77K) made up several percent when carbon atoms (0.1%) transformed into methane.

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