Hydrogen retention after boron carbide coating during plasma shot of tokamak 11

1
Hydrogen retention after boron carbide coating
during plasma shot of tokamak ?11-?
O.I. Buzhinskij , E.A. Azizov, V.G. Otroshchenko,
V.P. Rodionova, N.B. Rodionov, S.M. Sotnikov,
I.Ya. Shipuk, S.N. Tugarinov, A.G. Trapeznikov

• Presented by
• Prof. Oleg Buzhinskij
•  
• Head of Boundary Physics
• Federal State Unitary Enterprise State
  Scientific Center Troitsk, Institute for
  Innovation and Fusion Researches,
• Troitsk Moscow reg., 142190, Russia
• 
  June 1-4
• SALAMANCA,
  SPAIN
• 
  2008

2
Troitsk Moscow reg., Russia

• Experimental results on boronization in plasma
  shots of the tokamak T-11M are presented.
  Non-toxic and not explosive metacarborane
  C2H12B10 was used in the boron deposition
  process. Experiments have been carried out in
  shots with parameters toroidal field 1-1.2 ?,
  plasma current Ip 70??, average shot duration
  tp 150ms and electron density along the central
  chord ne 2.51013 cm-3. As a result of
  experiment, a dense film of 0.2 microns
  thickness with good adhesion to a surface has
  formed on the reference specimens after 8 second
  boronization.

SALAMANCA, SPAIN, 1-4 June, 2008
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Troitsk Moscow reg., Russia

• Crystalline boron carbide coating ?4?, produced
  by a method of the chemical vapor deposition in a
  reactor from the fluoride phase at the
  temperatures to 2000?, is widely used in the
  Russian tokamaks 1. The coating has a number of
  substantial advantages before graphites the
  small chemical and physical sputtering, low
  ion-stimulated desorption and radiation-accelerate
  d sublimation. As a result, a rate of the film
  erosion and sputtering at ion and plasma
  irradiation in the up-to-date accelerating and
  thermonuclear facilities is much below, than for
  graphites 1. These characteristics vary a
  little up to the temperatures of 1400?.

SALAMANCA, SPAIN, 1-4 June, 2008
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SALAMANCA, SPAIN, 1-4 June, 2008
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Troitsk Moscow reg., Russia

• Hydrogen capture in boron carbide in several
  times is less, than in fine-grained, dense
  graphites and CFC composites 2. This
  difference is increased with an irradiation dose,
  hydrogen capture in ?4? is saturated at doses
  about 1023 ?t/m2.

SALAMANCA, SPAIN, 1-4 June, 2008
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• Thermal conduction of boron carbide is not high
  (20 W/mK), but the coating of thickness up to 100
  µm, deposited on graphites with high thermal
  conduction, withstands high heat loads without
  its destruction and integrity losses. In all
  experiments the boron carbide coating showed a
  high resistance to heat loads without destruction
  and integrity losses, without changes in the
  chemical composition and material structure. The
  best coatings were at the deposition on graphites
  with a high thermal conduction (RGT or pyrolitic
  graphite) 5.

SALAMANCA, SPAIN, 1-4 June, 2008
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• Boron carbide coating produced by chemical
  vapour deposition has obvious advantages.
  However, because of complex technology of
  production at high temperatures a coating can be
  used in tokamaks only at the stage of initial
  mounting, reconstruction and modification of a
  discharge vessel. Boronization in a glow
  discharge in-situ results in to formation of thin
  amorphous films of thickness up to 100 nm 3,4.
  Recently, boron carbide films with a composition
  close to stochiometric ?4? have been obtained on
  the PISCES-B facility in the University of
  California, San Diego. Deposition rate was
  extremely high and achieved of 30 nm/sec, that
  approximately in one thousand times exceeds a
  rate of film deposition in a glow discharge.
  Thickness of deposited layer depended on
  discharge time and achieved of 40 µm

SALAMANCA, SPAIN, 1-4 June, 2008
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R - 0,7m a - 0,2m B? - 1? Ip - 70kA Poh
100kVt ?t 0,1s

• Crystalline metacarborane was placed in the
  glass container that connected with high-vacuum
  electromagnetic valve. Electromagnetic valve was
  connected to a diagnostic port of the T-11M
  tokamak discharge chamber through a vacuum gate
  valve.

SALAMANCA, SPAIN, 1-4 June, 2008
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• Boronization in the ?-11? tokamak was carried
  out after operation with lithium limiter without
  preliminary induction heating and cleaning of
  chamber by a glow discharge. In anterior shots
  (before boronization) atomic lithium, and also
  impurities came in plasma at the expense of an
  ion sputtering from chamber walls.

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A radiation spectrum of plasma before
boronization is shown by red colour. There is a
bright line of Li ion in the plasma radiation
spectrum. However, already after several shots
with carborane Li line and impurities lines
practically vanish from plasma radiation spectrum
(black line), and B ion line appears.
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During boronization DH ratio in peripheral
plasma changed up to 14. When a valve for
carborane injection was closed, from the plasma
radiation spectrum B line vanished, at the same
time lines of impurities have completely
vanished. The carborane injection valve has been
opened at the most for 50 ms before the plasma
shots start and start time of its opening could
be varied in a wide range.
SALAMANCA, SPAIN, 1-4 June, 2008
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The time dependencies of plasma current, plasma
density, of volts-seconds, hard X-rays detector
along a central chord for carborane container
temperature 100?
SALAMANCA, SPAIN, 1-4 June, 2008
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• The time dependencies of plasma current, plasma
  density, of volts-seconds, hard X-rays detector
  along a central chord for carborane container
  temperature 50?

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• Dependencies of a loop voltage before and after
  boronization

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• Time dependence of the B line intensity at
  opening of an injection valve for 50 ms before
  the plasma shot start (black line) and for 75 ms
  after shot start (red line)

SALAMANCA, SPAIN, 1-4 June, 2008
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The time dependencies hydrogen into a chamber
after (red line) and during boronization (black
line)
Troitsk Moscow reg., Russia
SALAMANCA, SPAIN, 1-4 June, 2008
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Time dependence of the B line intensity for
carborane container temperature 100? (red
line) and 60? (black line)
Troitsk Moscow reg., Russia
SALAMANCA, SPAIN, 1-4 June, 2008
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• optic microscope x 1500

Images of the boron-carbon film surface, SEM x
1400
optic microscope x 1500
SALAMANCA, SPAIN, 1-4 June, 2008
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coating images on the vacuum chamber T-11M
SALAMANCA, SPAIN, 1-4 June, 2008
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Conclusion
Troitsk Moscow reg., Russia

• Experiments on boronization in the tokamak T-11M
  plasma shots using metacarborane were carried
  out.
• Stabilization of a plasma column has improved,
  hydrogen recycling from the vessel walls has
  decreased.
• Plasma shot duration without disruption has
  essentially increased. At the density of
  ne1.31013?m-3, Ip 70?? a shot duration was
  350 ms and at the density of ne4.651013?m-3,
  Ip 70?? was 250 ms, the hard X-rays intensity
  in plasma shot and radiation losses have
  decreased, a plasma lifetime has increased almost
  in four times.
• High repeatability of experimental results has
  appeared.
• The film with microhardness ?10 600 and the
  thickness up to 0,2 µm at deposition rate of
  25 nm/s has been produced as a result of
  boronization.
• The impurities in wall areas were suppressed,
  high vacuum characteristics of the discharge
  chamber have stabilized.
• Presented technology opens the possibility of
  practical production of renewable structured
  boron-carbon coating with use of plasma shots in
  large-scale tokamaks, such as T-15M, ITER, DEMO.

SALAMANCA, SPAIN, 1-4 June, 2008
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References
Troitsk Moscow reg., Russia

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SALAMANCA, SPAIN, 1-4 June, 2008