OPTIMIZATION OF THE CONFIGURATION OF THE VACUUM PUMPS IN THE KEK 2.5-GEV LINAC

A pressure-distribution analysis was carried out for a vacuum unit of the KEK 2.5-GeV linac in order to improve the pressures at the radio f requency (rf) windows and accelerator columns. The characteristic matr ix ([G]) of the vacuum network geometry including the pumps was calcul ated for several configurations of the pumps. The results show that th ree additional pumps must be installed near to the rf window, so as to suppress any pressure rise due to outgassing in the long waveguides. A distributed configuration of the pumps causes more substantial reduc tion of the pressures at every node. However, it cannot cause a drasti c decrease in the pressure at the accelerator-column center, because o f its poor conductance. Pressure measurements at the nodes have also b een carried out for these configurations.