Impact of Peripheral D–Li-Plasma on Electrical Insulating Ceramics in the T-11M Tokamak and Its Thermodynamic Modeling

The interaction of peripheral D–Li-plasma with the protective ceramic elements of electrical porcelain, EP (xAl2O3⋅ySiO2), on the limiter of the T-11M tokamak has been studied. The calculated theoretical estimate of the maximum possible lithium capture is 6 mg (5 μg/discharge). The authors’ experimental method, based on the acid leaching with formic acid of the products of the interaction of EP with elemental lithium from the surface of dismantled protective ceramic elements, allowed us to obtain a practical estimate of Li-sorption equal to 3 mg (2.5 μg/discharge) (~50% of the theoretically calculated value) and to conclude that lithium chemisorption by the EP surface is irreversible. Li chemisorption is accompanied by the formation of lithium meta-aluminate (LiAlO2) and by the occurrence of the chemical transport reaction (CTR) due to the transfer of reduced aluminum vapors by the plasma flow (practical estimation of Al emission—4 mg (3 μg/discharge)) with the subsequent formation of Li–Al intermetallic compounds (mainly, AlLi5), mainly on the surface of the vertical limiter. The assessment of Li removal from the in-chamber circulation due to the formation of intermetallic compounds with Al is 2.5 mg (2 μg/discharge). Thus, the practical assessment of the total irreversible binding (and removal from circulation) of Li is 5.5 mg (4.5 μg/discharge). The thermodynamic model has been created and tested, which is adapted to the high (T >> ΘD) temperatures typical of plasma, and which permits the prediction of in-chamber processes in tokamaks. To adapt the model, the authors were the first to substitute polynomial dependences of heat capacities (Cp) on temperature T by their calculations according to Joule–Kopp’s law. The practical value of the work is that the long-term use of the protective ceramic elements promotes the growth of the chemically inert film of γ-LiAlO2 on the EP surface in situ.