An 805 MHz disk and washer accelerating structure with coaxial coupler for the Fermilab upgrade

The Disk and Washer (DAW) structure with four bi-periodic tees to support the washers has been studied at Fermilab for the Linac Upgrade by constructing two, 805 MHz, one-meter sections joined by a coaxial coupler. The coupler provides an rf drive port, an adjustable tuner, a vacuum port, and an enclosure for the installation of beam focussing and monitoring devices. This configuration is suitable for a high beta proton linear accelerator. The bi-periodic tee supports in the DAW structure suppress the TM11 mode at the operating frequency which has been a problem with previous designs. Frequency-mode spectra have been calculated and measured as well as the quantities Q, R/Q, and ZT2. The structure has been evacuated and operated at high power levels and high accelerating fields. 5 refs., 4 figs., 2 tabs