Photon stimulated desorption phenomena at the Taiwan Light Source vacuum system

The photon stimulated desorption (PSD) by the synchrotron radiation irradiated from the Taiwan Light Source (TLS) vacuum chambers were analyzed. The desorption behavior of the various gas species were compared by either adjusting the electron beam orbit and hitting the photons on the fresh chamber walls or turning off the pumps. The dominated gases during the earlier years' operation are the H/sub 2/, in concentration of >90%, followed by other gases, e.g. CO, H/sub 2/O, CH/sub 4/, etc. However, some of the massive gas species, e.g. CxHy, CxFy, were observed after replacing the new vacuum parts or unsuitable baking of the O-ring gate valves at higher temperature. The contaminated gases are to be reduced by beam-self cleaning treatment. Planning in upgrading the storage ring vacuum system is also described.