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SLAC Technical Note: SLAC-TN-20-001
SLAC Release Date: January 6, 2020
Preliminary results for in situ cleaning of B4C-coated FEL mirrors using oxygen plasma.
Peter, Stefan.
An in situ oxygen plasma cleaning process has been applied to LCLS B4C-coated Kirkpatrick-Baez (KB) mirrors. After a total of five hours treatment, the initial carbonaceous contamination stripes, acquired over 7 years of FEL beam irradiation, were visibly reduced to barely detectable. After treatment, the output photon flux showed a reflectivity improvement between ~20% and ~170%, depending upon the photon energy. Further characterization, including detection of possible sputter-deposited impuri... Show Full Abstract
An in situ oxygen plasma cleaning process has been applied to LCLS B4C-coated Kirkpatrick-Baez (KB) mirrors. After a total of five hours treatment, the initial carbonaceous contamination stripes, acquired over 7 years of FEL beam irradiation, were visibly reduced to barely detectable. After treatment, the output photon flux showed a reflectivity improvement between ~20% and ~170%, depending upon the photon energy. Further characterization, including detection of possible sputter-deposited impurities and improvement in KB focusing properties, are planned following return of FEL beams, at the conclusion of the current six-month downtime, in June, 2017. Preparatory, off-line measurements suggest that the process is both "safe and effective" for B4C-coated mirrors. Test depositions of 50 nm amorphous carbon could be removed with high selectivity against B4C erosion, with no change in treated/untreated surface roughness. Nevertheless, sputter-deposited impurities from adjacent components may be an issue, as seen in soft x-ray reflectivity studies, where surface reflectivity restoration remained imperfect. Show Partial Abstract
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  • Interest Categories: Instrumentation/Development, Optics, Synchrotron Radiation, X-Ray Free Electron Laser