ADSORPTION STATES OF PROTIUM AND DEUTERIUM IN POLYMER HYDROCARBON FILMS FROM T-10 TOKAMAK

1. ASEVA WORKSHOP 2008 WS-23 9th International Workshop on Hydrogen Isotopes in Fusion Reactor Materials Salamanca, Spain, June 2-3, 2008 ADSORPTION STATESOF PROTIUM AND DEUTERIUMIN POLYMER HYDROCARBON FILMSFROM T-10 TOKAMAK V.G. Stankevich1, N.Yu. Svechnikov1, L.P.Sukhanov1, K.A .Menshikov1, A.M. Lebedev1, B.N. Kolbasov1, Y.V. Zubavichus1, D. Rajarathnam2 1 Russian Research Center Kurchatov Institute, Moscow 123182, Russia 2 National University of Singapore, Singapore 117576

2. 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

3. Flakes’ formation conditions Tokamak T-10 (RRC Kurchatov Institute) Movable limiter and stationary annular diaphragm, made of a fine grain graphite MPG-8. The total duration of VV conditioning modes and plasma discharges in 2002: ♦heating up to 200С – 897 hours; ♦inductive discharges – 35 hours H2 plus 270 hours (99% D2 + 1% H2); ♦Не glow discharges – 86 hours; ♦D- plasma discharges – 1620 s.

4. Samples 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 = 0.2 - 0.4 reddish-gold D/C = 0.5 - 0.8 H/C = 0.1 - 0.2 Thickness 20–30 µm, size S ≈0.5 cm2 Structure of soft a-C:Hfilms is rather close to that of flakes Plasma facing side of flakes

5. Experimental methods • Thermal desorption spectroscopy (TDS) of H2, D2, HD gases • X-ray Diffraction

6. HD D2 TDS curves for D2(H2) consist of 2 groups of peaks: at 450–800 Kand 900–1000 K Thermodesorption spectra H2 Heating rate dT/dt = 10 K/min

7. Comparison of gold and dark flakes for H2 isotope for D2 isotope The whole TDS structure of gold and dark flakes cannot be regarded as totally different, i.e. their adsorption sites have similar features

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

9. Raman spectra Graphite milled in D2-atmosphere [2] TDS spectra crystallites less than 40 Å Similarity of spectral features allow to use data already reported on activation energies for interpretation of the present TD spectra. As a result, two main adsorption states of hydrogen isotopes were revealed from TDS. [2] Orimo et al., J.Appl.Phys. 90 (2001) 1545.

10. 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) = 0.214 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.

11. Two mechanismsof thermal desorptionof H2, D2, HDin flakes

12. 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)

13. CONCLUSIONS 1.Two main adsorption states of hydrogen isotopes were revealed from TDS: 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.

14. TEAM

15. Gracias por su atención

17. Infrared reflectance spectra of golden and dark flakes Low energy part of spectra ●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.