Angular distributions of photon stimulated desorption in a vacuum duct observed by using a unidirectional detector

Abstract

Pressures in the vacuum duct of the electron storage rings depend on photodesorption. A multicapillary-type mass spectrometer was applied to observe local outgassing rates in the duct, in which the duct surfaces were irradiated by directly incident photons and/or by scattered photons. Local outgassing rates were nonuniform along the periphery of the duct. The desorption rates at the directly incident point were higher than at the other surfaces when photon dose was less than 200 mA h. At over 9000 mA h the rates at that point decreased more, while the desorption rates at the other surfaces decreased less. Angular distributions of photocurrent were also measured. The distributions were almost uniform except near the directly incident point.