高周波放電および直流グロー放電下のステンレス鋼真空壁における水素同位体交換脱離

Abstract

The saturation and replacement of hydrogen isotopes implanted into 304 stainless steel vacuum wall at 300 K under RF discharge and RF-DC glow discharge has been studied from partial pressure measurements of desorbed isotopes. The bombarding ion flux on the wall are 12×1013 ions/cm2·s. The energy of H2+ or D2+ ion is determined by acceleration with space potential produced in discharge plasma, and is about 40 eV for RF discharge and 300 eV for RF-DC glow discharge. The hydrogen and deuterium saturation concentrations in the wall surface are 4.2×1015 and 1.3×1016 molecules/cm2 for ion bombardment of 40 eV and 300 eV, respectively. Nearly 90% of desorbed gas in isotopic exchange process is HD molecule. The desorption rate is expressed by inverse-exponential function with time. The time constant is proportional to isotope concentration and inversely proportional to bombarding ion flux.Experimental results show that the local mixing model (LMM) is still valid for such ion implantation in lower energy region less than 1 keV. But LMM must be corrected for explanation of the isotope exchange process under plasma ion bombardment at 40 eV. Two-component inverse-exponential functions are observed in the replacement. The function of component 2 is explained by adopting an effective trapping coefficient, although another function of component 1 can be described by LMM.