AVS 49th International Symposium
    Vacuum Technology Tuesday Sessions
       Session VT-TuP

Paper VT-TuP9
Vacuum Chamber with Distributed Titanium Sublimation Pumping for the G-Line Wiggler at Cornell High Energy Synchrotron Source

Tuesday, November 5, 2002, 5:30 pm, Room Exhibit Hall B2

Session: Poster Session
Presenter: Y. Li, Cornell University
Authors: Y. Li, Cornell University
Y. He, Cornell University
N.B. Mistry, Cornell University
Correspondent: Click to Email
This paper describes a 3-meter long vacuum chamber for the newly installed wiggler magnet at the Cornell Electron Storage Ring (CESR) for the synchrotron light beam line of the Cornell High Energy Synchrotron Source (CHESS). Copper was chosen as the main chamber material for its good electric and thermal conductivities. Proper mechanical design and welding procedure were implemented to meet very tight tolerances to ensure adequate vertical aperture for the stored beams in CESR while allowing the required small wiggler gap. Distributed titanium sublimation pumping is incorporated along 3-meter length of the chamber to provide sufficient pumping speed and capacity for CESR and CHESS operations. The chamber pumping performance was evaluated prior to the installation. Linear distributed pumping speeds at the beam line of ~800 liter/sec/meter for N@sub 2@ and CO and ~4200 liter/sec/meter for H@sub 2@ were measured. The pumping speed is determined by the gas conductance of the slotted copper screen between the beam line and the TiSP compartments. The measured pumping capacities for N@sub 2@, CO and H@sub 2@ are ~1.0, ~2.0 and ~77 torr-liter, respectively, for each titanium sublimation cycle. Measurements also showed that CO molecules adsorb on the N@sub 2@ and H@sub 2@ saturated titanium films with virtually the same initial sticking coefficient as on a fresh titanium film. Detail analyses indicated very different CO adsorption mechanisms between the N@sub 2@ and H@sub 2@ saturated titanium films. While the replacement of surface H@sub 2@ by CO was observed, little desorption of N@sub 2@ was measured. Operational experience showed excellent vacuum pumping performance over seven months after the chamber installation.