(1) The main impurities in FT are oxygen and iron. Iron impurities are negligible at high density (nFe < 10−4 ne). Radiation losses account for 20-40% of the total input power in all conditions [1, 2].(2) FT is provided with a complete poloidal limiter made of stainless steel. The same material is used for the vacuum chamber. To a good approximation, the volume inside the outermost closed flux surface equals 2π2Rgeoab.