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

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ADSORPTION STATESOF PROTIUM AND DEUTERIUMIN
POLYMER HYDROCARBON FILMSFROM T-10 TOKAMAK
ASEVA WORKSHOP 2008 WS-23 9th International
Workshop on Hydrogen Isotopes in Fusion Reactor
Materials Salamanca, Spain, June 2-3, 2008

• 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

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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

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Flakes formation conditions
Tokamak T-10 (RRC Kurchatov Institute)
minor radius 0.39 m
major radius 1.5 m
minor radius of plasma 0.35 m
toroidal field 2.8 T
plasma current 200 - 400 kA
discharge time 1 s
electron temperature of core plasma 1 keV
ion temperature 450 - 700 eV
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??
897 hours ? inductive discharges 35 hours
H2 plus 270 hours (99 D2 1 H2) ? ?? glow
discharges 86 hours ? D- plasma discharges
1620 s.
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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 2030 µm, size S 0.5
cm2
Plasma facing side of flakes
Structure of soft a-CH films is rather close to
that of flakes
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Experimental methods

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

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Thermodesorption spectra
H2
Heating rate dT/dt 10 K/min
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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
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Deuteriumthermodesorption spectra 1
?) gas charged graphite
1 H. Atsumi et al., J. Alloys Comp. 356 (2003)
705
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Graphite milled in D2-atmosphere 2
Raman spectra
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.
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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)
0.3350.345 nm in-plane hexagonal structure at
d(100) 0.214 nm) and are amorphous. The
dominant diffraction component at d0.77 nm
corresponds to a certain characteristic
dimension of poorly ordered structure of flakes.
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Two mechanismsof thermal desorptionof H2, D2,
HDin flakes
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CONCLUSIONS 1. Two main adsorption states of
hydrogen isotopes were revealed from TDS
Temperature 450 600 ? 900 1000 ?
Adsorption state Weak (physisorption) Strong (chemisorption)
Desorption Mechanism Hopping diffusion Resonance type mechanism
Activation energy 0.65 eV/H 1.25 eV/H
Genesis of adsorption state H2 cleaning discharge storage at atmosphere ? D- plasma discharge (99 D2 1 H2) cleaning
2. Carbon flakes differ substantially from
graphite and are amorphous. The dominant
diffraction component at d0.77 nm corresponds to
a certain poorly ordered structure of flakes.
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TEAM
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Gracias por su atención
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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 CH 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 CH, CC, OH, CO
interconnected adsorbates, i.e. more short carbon
network structures composed mainly of CH
aromatic modes at 700900 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.