Protective coatings for plasma facing components in thermonuclear reactors

The plasma facing components in future thermonuclear confinement experiments have to withstand high stationary heat loads during normal operation and severe thermal shocks during off-normal conditions (so-called disruptions). In these transient events on the first wall, energy depositions up to 2 MJ m⁻² can occur with pulse durations of the order of 1 ms. To improve the performance of the plasma and to protect it against high-Z impurities from metallic structures, boron carbide coatings have been used successfully in different fusion experiments. Thick coatings of this material have been prepared by plasma spraying, a technique which also offers potential for in-situ repair of damaged coatings inside the torus.

Coatings with thicknesses of several hundred micrometers on different substrates (graphites, carbon fiber composites, stainless steel and refractory metals) have been tested in high heat flux test facilities at heat loads simulating the normal operation and disruption conditions. In addition, a limited number of coated tiles have been installed in fusion relevant tokamak experiments such as TEXTOR, JET or JT-60U.