Pressure distribution analysis of the KEK 2.5-GeV linac

Since the vacuum system of a linac comprises many conduit pipes (such as accelerator columns, waveguides and pump ducts) it is a multiply connected network. In such a network having n nodes, by introducing an nxn Green-function matrix determined by the network geometry, the pressure (pi) at the i th node can be expressed as (pi)=[Gij](Qj), where (Qj) is the gas load. This type of analysis was applied to a KEK 2.5-GeV linac with 14 nodes, 19 branchs and 2 pumps within the unit. The results show that the outgassing rate of the accelerator columns made of oxygen-free copper decreases from ∼10-10 to ∼10-11 Torr 1 cm-2s-1 after high-power conditioning. (author)