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

Abstract

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.