Some problems arising due to plasma–surface interaction for operation of the in-vessel mirrors in a fusion reactor

Effects of two contradictory processes on the survivability of the in-vessel mirrors for diagnosing plasma in a fusion reactor, namely, the sputtering by charge exchanged atoms and deposition of eroded material, are analyzed in detail using results of simulation experiments. The degradation rate of mirrors bombarded long-term by keV energy range ions of deuterium plasma was found to depend strongly not only on the mirror material but also on its initial structure and energy of projectiles. The highest resistance was demonstrated by mirrors fabricated of monocrystal W and Mo and the lowest by mirrors fabricated of hot-pressed Be. As for the effect of mirror contamination, an effective reflectance was measured and calculated for some metal mirrors coated by thin films typical for existing fusion devices or for a fusion reactor: boron, carbon, and beryllium.