Review of in Situ Boronization in Contemporary Tokamaks

A review of some characteristic features of the boronization process, properties of boron-carbon films, and the influence of these features on tokamak discharges is presented. Boronization, as defined here, is a plasma chemical vapor deposition of a thin a-B/C:H film on the first wall of fusion reactors. As a result of boronization, oxygen, carbon, and heavy impurities (e.g., iron, nickel, and chromium) are suppressed, and hydrogen recycling is reduced, which substantially improves the characteristics of tokamak discharges. A two-stage complex protection of both the first wall by boronization and of limiters, divertor plates, and radio-frequency antennas by the application of thick B4C coatings provides further improvement of tokamak plasma parameters.