Modifications of thin coatings by heat treatment: Behavior of redeposited material on the first wall of fusion devices during plasma wall interaction

In magnetic confinement experiments the first wall and especially its high heat flux components (e.g., limiter, armor tiles) are subjected to plasma wall interaction which will cause physical and chemical erosion. The eroded wall material can enter the plasma where it contributes to plasma radiation losses especially when materials with medium or high atomic numbers (Z) are used. To avoid or reduce these objectionable processes, the application of thin low‐Z coatings for the first wall has been discussed and is occasionally already in use. A considerable disadvantage of thin films is their morphological instability under thermal loading. The stability of thin metallic coatings on different substrates was investigated in laboratory experiments under fusion‐relevant heat loading conditions and also under realistic conditions in magnetic confinement experiments.