Test of the boron-containing coating of the graphite limiter in the T-10 tokamak

Results of test investigations on the behavior of different carbon-based materials with boron carbide coverings as operation elements of the rail limiter in T-10 are reported. This rail limiter consisted of some elements made from MPG-8 graphite, uglesitall USB-15, and pyrolytic graphite. Some MPG-8 and pyrolytic graphite elements were covered by a B-C film with a thickness of 200 μm. The limiter was exposed to about 2500 operation pulses with the following plasma parameters: ne = (0.5-1.0)x1013 cm-3, Te = 20-50 eV, plasma flux F = 5x1018-2x1019 cm-2 s-1, power load up to 5 MWm-2 in ohmical discharge and up to 20 MWm-2 in ECR heating discharge. The test revealed that the erosion of the B-C films is 50-100% less than of MPG-graphite. However, the total sputtering both for the graphite and for the B-C folm is much higher than predicted from model experiments. Melting of the B4C coating was observed on MPG substrate, but not on the substrate from the pyroloytic graphite, due to its high thermal conductivity. No cracks or flakes typical for graphite material were observed on the B4C coating. (orig.)