ADSORPTION STATES OF PROTIUM AND DEUTERIUM IN POLYMER HYDROCARBON FILMS FROM T-10 TOKAMAK V.G. Stankevich 1, N.Yu. Svechnikov 1, L.P.Sukhanov 1, K.A.Menshikov 1, A.M. Lebedev 1, B.N. Kolbasov 1, Y.V. Zubavichus 1, D. Rajarathnam 2 1 Russian Research Center Kurchatov Institute, Moscow , Russia 2 National University of Singapore, Singapore ASEVA WORKSHOP 2008 WS-23 9th International Workshop on Hydrogen Isotopes in Fusion Reactor Materials Salamanca, Spain, June 2-3, 2008

Our goals Search for ways to decrease tritium accumulation rate inside the vacuum vessel Investigation of the electronic states of Tokamak erosion products Determination of the hydrogen-carbon bonding states for hydrogen isotopes, and their thermal stability

Flakes’ formation conditions Tokamak T-10 (RRC Kurchatov Institute) The total duration of VV conditioning modes and plasma discharges in 2002: ♦ heating up to 200  С – 897 hours; ♦ inductive discharges – 35 hours H 2 plus 270 hours (99% D 2 + 1% H 2 ); ♦ Не glow discharges – 86 hours; ♦ D- plasma discharges – 1620 s. minor radius0.39 m major radius1.5 m minor radius of plasma 0.35 m toroidal field 2.8 T plasma current kA discharge time 1 s electron temperature of core plasma1 keV ion temperature eV Movable limiter and stationary annular diaphragm, made of a fine grain graphite MPG-8.

Samples H/C = Thickness 20–30 µm, size S ≈0.5 cm 2 Flakes were collected in the shadowed areas, between two sidewalls forming the first wall where temperature was close to room temperature. The color of flakes strongly varies with D/C ratio: dark-brown D/C = reddish-gold D/C = Plasma facing side of flakes Structure of soft a-C:H films is rather close to that of flakes

Experimental methods Thermal desorption spectroscopy (TDS) of H 2, D 2, HD gases X-ray Diffraction

Thermodesorption spectra Heating rate dT/dt = 10 K/min H2H2 HD D2D2 TDS curves for D 2 (H 2 ) consist of 2 groups of peaks: at 450–800 K and 900–1000 K

Comparison of gold and dark flakes The whole TDS structure of gold and dark flakes cannot be regarded as totally different, i.e. their adsorption sites have similar features for H 2 isotopefor D 2 isotope

Deuterium thermodesorption spectra [1]: а) gas charged graphite [1] H. Atsumi et al., J. Alloys Comp. 356 (2003) 705 b) ion implanted graphite с) nano-structured graphite milled in hydrogen atmosphere

Graphite milled in D 2 -atmosphere [2] Raman spectra crystallites less than 40 Å TDS spectra As a result, two main adsorption states of hydrogen isotopes were revealed from TDS. Similarity of spectral features allow to use data already reported on activation energies for interpretation of the present TD spectra. [2] Orimo et al., J.Appl.Phys. 90 (2001) 1545.

X-ray diffraction ● The sample is essentially non-crystalline. The XRD profile can be deconvolved into 2 Gaussians which correspond to the interplanar distances of 0.77 nm (large peak) and 0.28 nm (small peak). ● The carbon flakes differ substantially from graphite (graphene layers are observed at d (002) = 0.335–0.345 nm; in-plane hexagonal structure at d(100) = nm) and are amorphous. The dominant diffraction component at d=0.77 nm corresponds to a certain characteristic dimension of poorly ordered structure of flakes.

Two mechanisms of thermal desorption of H 2, D 2, HD in flakes

Hopping diffusion between weakly bonded states on structural elements (nanopores), followed by a fast pair recombination (2-nd order reaction) Resonance mechanism for strongly bonded states (1-st order reaction)

CONCLUSIONS 1. Two main adsorption states of hydrogen isotopes were revealed from TDS : Temperature450 – 600 К900 – 1000 К Adsorption state Weak (“physisorption”) Strong (chemisorption) Desorption MechanismHopping diffusionResonance type mechanism Activation energy≈ 0.65 eV/H≈ 1.25 eV/H Genesis of adsorption state H 2 cleaning discharge & storage at atmosphere ? D- plasma discharge & (99% D 2 + 1% H 2 ) cleaning 2. Carbon flakes differ substantially from graphite and are amorphous. The dominant diffraction component at d=0.77 nm corresponds to a certain poorly ordered structure of flakes.

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Infrared reflectance spectra of golden and dark flakes ●Spectral differences between golden and dark flakes are correlated with concentration differences of carbon deposits and to the degree of C–H hybridization. The dark flakes have less hydrogen adsorption which could be lead to much carbon – carbon network. Dark films have a more fragile and weak C–H, C – C, O – H, C=O interconnected adsorbates, i.e. more short carbon network structures composed mainly of C–H aromatic modes at 700 – 900 cm -1. ● The CD2,3 modes around 2200 cm -1 (main D-tracing modes) are weaker for dark flakes, but their shape is similar to that of golden flakes, therefore these modes are not introduced into the carbon net, but form the CD2, CD3 end-groups connected to the disordered carbon network. Low energy part of spectra