Ion–solid interaction in fusion reactors

The impact of energetic ions and atoms from the plasma on the first wall causes serious problems in achieving and maintaining a thermonuclear plasma. Simple model calculations show that sputtering by working gas particles is the main source of impurities in the plasma. Wall erosion is estimated to be up to ∠0.1 mm/yr. Recent experiments show that blistering due to ions and atoms in the mean energy range of the plasma particles (1–20 keV) does not contribute to wall erosion and may be completely avoided. The charge and energy distributions of working gas particles backscattered from the first wall is largely responsible for the impact of high energy resonant charge exchange neutrals on the wall. The energy distribution of backscattered neutrals differs significantly from that of ions. High amounts of gas may be trapped in the first wall, but a reemission factor of one will be attained for most materials after a short starting period. High trapping efficiencies for hydrogen even at very high doses are found in materials like Ti and Zr. This may be helpful in increasing the pumping efficiency of a divertor.