142190, Troitsk Moscow region, RussiaEXAMINATION OF THE VESSEL CONDITION OF Т11-M

TOKAMAK AFTER TWO-YEAR OPERATION WITH LITHIUM LIMITER

O.I. Buzhinskij, V.A. Barsuk, V.G. Otroshchenko

Prepared byProf. Oleg Buzhinskij Head of Boundary PhysicsFederal State Unitary Enterprise State Scientific Center Troitsk, Institute for Innovation and Fusion Researches, 142190, Troitsk Moscow reg., Russiabuzh@triniti.ru

142190, Troitsk Moscow region, Russia

Problem of a choice of constructional materials for protective shields , limiters, divertor plates of modern tokamaks, including ITER, remains to present day open. As the alternative decision of this problem, application in a tokamak liquid metal as the renewable coating is proposed. On the tokamak Т11-M within two years tests of the lithium limiter on the basis of capillary - porous structure have been carried out. Experiments were carried out in conditions of He- and Н- plasma discharges at RF-heating.

R – 0.7m a – 0.25mBт - 1Т Ip - 90kA Poh~100kVt∆t ~ 0.1-0.2 s

VISUAL EXAMINATION OF THE T-11M VESSEL CONDITION

Visual inspection of the vacuum chamber and ports surface has shown

availability of appreciable amount of a light grey color substance, covering by a loose layer the significant surface areas of chamber and ports wall, especially near to the lithium limiter location, and also a usual metal incrustation with temper colors through of various thermal loadings on the vessel material. The surface of molybdenum chamber wall had numerous damages as craters in depth from 8 up to 15 microns.

Below, has shown the photos of section placed close to the Li limiter position.

Vessel section in the Li limiter position

142190, Troitsk Moscow region, Russia

Inner part of vessel section near the Li limiter position

142190, Troitsk Moscow region, Russia

Outer part of vessel section near the Li limiter position

142190, Troitsk Moscow region, Russia

The same T-11M vessel section after boronization in plasma shots.

The X-ray microanalysis of a deposited matter from the molybdenum first wall surface near a lithium limiter has shown, that into composition of the given substance there are Мо in the main and insignificant amount of copper.

X-ray difractometer analysis has shown, that a substance on the Mo first wall is a mix of phases: basic phase Li2CО3 and Li2МоО4, that approximately is one third of all substance composition.

142190, Troitsk Moscow region, Russia

x 90

142190, Troitsk Moscow region, Russia

The X-ray microanalysis of a deposited matter from the bottom port wall, also located nearby to a lithium limiter, there are the same elements and in addition Fe in a small amount. Because of the tool restrictions of the given analysis method a detection capability of lithium traces has missed. X-ray difractometer analysis has shown in the substance composition from a port surface as the main phase it was found LiОН-Н2О, there is also Li2СО3 phase. However, repeated analysis of the substance, fullfilled once more in three weeks has shown, that LiОН-Н2О phase completely disappears, and Li2СО3 phase is the main phase. Phase state of Мо in the substance composition from a port clear was not revealed.

x 1000

x 100

142190, Troitsk Moscow region, Russia

The microphotographies of the molybdenum first wall surface, obtained on scanning electron microscope in secondary and back-scattered electrons, and also exposure of the same area in X-rays Mo-La1,2 и K-Ka1,2 have shown, that surface represents a deposited layer with great number of craters on separate areas in depth from 8 up to 15 microns. The undamaged surface includes Мо with a Fe impurity.

x 90

142190, Troitsk Moscow region, Russia

Let's consider possible mechanisms of a formation of the discovered compounds. Yet at a stage of the tokamak working operation the lithium cans to interact with hydrogen of an operating environment at the temperature about 500С:

2Li + Н2 —> 2LiH Moreover, the oxygen existing in the discharge vessel at an attainable

underpressure degree on the given facility and the temperature 500С intensively interacts with the chamber wall molybdenum with formation of a volatile oxide:

2Мо + ЗО2 —> 2МоО3

In the same conditions there is also an oxidation of lithium: 4Li + О2 —> 2Li2O (at the temperature 200С this process is

very active). At the temperature 1100С it is probably a direct interaction of oxides with

formation of the lithium molybdate: Li2O + МоОз —> Li2MoO4 so, for example, are formed the lithium

niobates and tungstates).

Conclusion 142190, Troitsk Moscow region, Russia

The analysis of the molybdenum first wall surface after work with a lithium limiter has shown presence of a Li deposited layer with numerous local damages as craters in depth from 8 up to 15 microns. The undamaged surface of the first wall includes Мо with impurities of Fe and also K and Са in several areas.

Chemical compounds of lithium: Li2CO3, Li2MoO4 и LiOH-H2O have been identified during the analysis of substance composition and products of interaction with the plasma, forming on the first wall during plasma shots.

Graphite limiter surface with a boron carbide coating has not shown any changes.