Accelerator Vacuum Problems. In-Line Oil Trapping between the Stanford Linear Accelerator and the Beam Switchyard

Abstract

The thirty accelerator sectors (each 330 feet long) of the two-mile machine will be evacuated with sputter-ion pumps to pressures low enough to limit rf breakdown and multipactor problems. After the beam leaves the accelerator it will be switched by pulsed magnets to one or more of the experimental areas through the 1000-foot beam switchyard. Due to the nature of the equipment in the beam switchyard and the requirements for inexpensive, non-elastomeric, remotely operable couplings, there will be a high probability for virtual and real leaks and a consequent need for continuous high throughput pumping. Oil diffusion pumps are therefore used to evacuate the four branching beam tubes of the beam switchyard. Some kind of in-line oil trap is needed to separate the clean, low pressure (10-7 torr), ion-pumped accelerator from the oil-pumped (10-4 torr) beam switchyard end of the machine. This trap should limit the amount of oil and organic fractions passing back through to the accelerator and should provide some of the impedance necessary to obtain the three-order-of-magnitude pressure difference between accelerator and switchyard. The pressure difference will be maintained by differentially pumping on each of two in-line vacuum impedances. One of these impedances will be a standard 10-foot section of disk-loaded waveguide and will act as an oil trap. When refrigerated, such a trap had measured transmission probabilities of 10-9 to 10-6 for heavy hydrocarbons.