Test fabrication of a copper beam duct for the KEK B-factory

A trial model of a copper beam duct for the KEK B-Factory was fabricated and gas desorption rates were measured. The duct consists of a cooling channel, a beam channel and a pump channel, which were extruded separately and welded each other by the electron beam welding. The duct received only ultrasonic cleaning in a freon bath. The ultimate total pressure was about 4/spl times/10/sup -10/ Torr after baking at 150/spl deg/C for 48 hours and the thermal gas desorption rate was calculated to be about 1.5/spl times/10/sup -12/Torr. l/(s/spl middot/cm/sup 2/) in N/sub 2/ equivalent. The measurement of the photon stimulated gas desorption rate was performed using synchrotron radiation with a critical energy of 26.3 keV from the TRISTAN Accumulation Ring. The photo-desorption coefficients of the order of 10/sup -2/ molecules/photon were observed for main gases desorbed at the initial stage. These high gas desorption rates indicate that more careful surface preparation must be necessary.<
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