hydrogen retention after boron carbide coating during plasma shot of tokamak Т11-М presented by...

Hydrogen retention after boron carbide coating during plasma shot of tokamak Т11-М

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

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

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 Т, plasma current Ip = 70кА, average shot duration tp ~ 150ms and electron density along the central chord ne ~ 2.5∙1013 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.

Troitsk Moscow reg., Russia

SALAMANCA, SPAIN, 1-4 June, 2008

Crystalline boron carbide coating В4С, produced by a method of the chemical vapor deposition in a reactor from the fluoride phase at the temperatures to ~ 2000°С, 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-accelerated 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°С.



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 В4С is saturated at doses about 1023 аt/m2.



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].



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 В4С 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



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.



R - 0,7ma - 0,2mBт - 1ТIp - 70kAPoh ~ 100kVt∆t ~ 0,1s

Boronization in the Т-11М 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.





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.



During boronization D:H ratio in peripheral plasma changed up to ~ 1:4. 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.



The time dependencies of plasma current, plasma density, of volts-seconds, hard X-rays detector along a central chord for carborane container temperature 100°С

The time dependencies of plasma current, plasma density, of volts-seconds, hard X-rays detector along a central chord for carborane container temperature 50°С



Dependencies of a loop voltage before and after boronization



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)





The time dependencies hydrogen into a chamber after (red line) and during

boronization (black line)



50 100 150 200 2500

100000

200000

300000

400000

Inte

nsity (

a.u

.)

Time (msec)

22673-BIII (60 C0)

22691-BIII (100 C0)

Time dependence of the B line intensity for carborane container temperature

100°С (red line) and 60°С (black line)

optic microscope x 1500



Images of the boron-carbon film surface, SEM x 1400

optic microscope x 1500



coating images on the vacuum chamber T-11M

Conclusion• 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 ne=1.3∙1013сm-3, Ip = 70кА a shot duration was ~350 ms and at the density of ne=4.65∙1013сm-3, Ip = 70кА 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 Н10 – 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.



References• [1] O.I. Buzhinskij, M.I. Guseva, G.V. Gordeeva, J.

Nucl. Mater. 196-175 (1990) 262• [2] L. Begrambekov, O. Buzhinskij, A. Gordeev, E.

Miljaeva, P. Leikin and P. Shigin, Physica Scripta, 108 (2004) 72.

• [3] J. Winter, H.Esser, L. Konen, H.Reimer, L. Grobush, P. Wienhold, J. Nucl. Mater. 162-164 (1989) 713.

• [4] O.I. Buzhinskij and Yu.M. Semenets, Fusion Techn. 32 (1) (1997) 1.

• [5] O.I. Buzhinskij, V.G. Otroshchenko, D.G. Whyte, M. Baldwin, R.W. Conn, R.P. Doerner, R. Seraydarian, S. Luckhardt, H. Kugel, W.P. West, J. Nucl. Mater. 313-316 (2003) 214.

• [6] V.A. Evtikhin, I.E. Lyublinski, A.V. Vertkov, S.V. Mirnov, V.B.Lazarev, Proc. 16 IAEA Fusion Energy Conference, IAEA 3 (1997) 659.



hydrogen retention after boron carbide coating during plasma shot of tokamak Т11-М presented by...

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