Boron Carbide as a Protective Material for Plasma-Facing Elements of Plasma and Thermonuclear Facilities

The properties of boron carbide and its coating, which seem important for the plasma-facing material in thermonuclear facilities, are presented. The basic steps for boron carbide (B4C) coating using carborane (C2B10H12) as the initial material are reported. It has been shown that is not susceptible to “chemical sputtering.” The sputtering rate of B4C is 3–4 times and the emission of carbon atoms is 15–20 times less than that of graphite and changes slightly up to 1500 K. Trapping of hydrogen isotope ions into the B4C coating tends to saturation at irradiation doses of about 7 × 1023 at/m2. A method for low-temperature “detritization” of the coating is proposed. Conditioning the coating by irradiating it with hydrogen ions with an energy of 50 eV left ≈8% of the introduced deuterium ions in it. The results of several cycles of thermal cycling of coatings are presented. In particular, a B4C coating with a thickness of 5 µm on tungsten up to 2000 K retained the composition B:C ≈ 3.8:1, melted in the range of 2500–3670 K, and changed the composition to B : C ≈ 1.2:1, but remained continuous, without peeling. The results of improvement of plasma parameters after deposition of a boron carbide coating on the first wall of the T-11M tokamak and in the PISCES-B facility are presented. The coating deposition rate reached 30 nm/s. The possibility of plasma-chemical conversion into gas and removal of boron carbide erosion products from facilities is reported.