Vacuum Systems

The three major vacuum systems serving the two-mile accelerator, the optical alignment system light pipe, and the beam switchyard (BSY) transport vacuum chambers are located as shown in Fig. 23-1. The accelerator vacuum system must maintain a very high vacuum in the accelerator to prevent RF electrical breakdown and electron scatter. Thirtytwo subsystems evacuate the accelerator to a design pressure of 5 x 10 ~ torr at the center of the individual 10-ft long sections of disk-loaded waveguide that comprise the beam envelope. Separate subsystems are provided for the injector, for the positron source, and for each of the thirty sectors of the accelerator. The subsystems are interconnected only through the 2-mile length of the disk-loaded waveguide except for a normally closed cross-tie between the injector and Sector 1 subsystem piping. Mobile cryosorption pump sets evacuate the individual subsystems from atmospheric pressure to a level at which the sputter-ion pumps can take over to produce the operating vacuum. The alignment light pipe vacuum system evacuates the tubular aluminum girders which support the two-mile accelerator and the central beam tube in the BSY. The design pressure of 1 x 10 ~ torr prevents deflection of light rays used for optical alignment. The girders are interconnected by flexible metal bellows. A single pumping station is located at the end of Sector 30. The initial pumpdown from atmospheric pressure is accomplished using highcapacity mechanical vacuum pumps. The vacuum is maintained at the operating level by a diffusion-ejector vacuum pump backed by a mechanical pump. The beam switchyard vacuum system evacuates the BSY beam transport vacuum chambers to an average design pressure of 1 x 10 " torr to permit passage of electron and positron beams. Normally open valves are provided by which adjoining chambers can be segregated into seven independently