Hydrogen ion bombardment damage in stainless steel mirrors

Experiments have been performed to evaluate the changes in surface structure and the resulting effects on the optical properties of stainless steel due to hydrogen ion irradiation. Stainless steel (SS) is a standard material used for in-vessel components, including the first mirrors (FMs), in some current generation fusion devices. Optical microscopy, interferometry, scanning electron microscopy (SEM) and ellipsometry were used to characterize the surfaces. Results are presented for the bombardment of SS mirrors with H3+ ions having various fixed energies (0.3, 0.65, and 1.5 keV/H+), with ion flux densities of (0.5-2) × 1020 H+/m2s and fluences of ∼2.2 × 1024 H+/m2. Variation of the ion energy at a constant fluence had a considerable effect on the damage structure that forms on the SS mirror surfaces. Possible mechanisms for the ion energy effect on the surface are discussed and a model of the damaged surface layer is proposed.