Development of Disk-and-Washer Cavity in KEK

The behavior of the deflecting mode of the disk and washer structure was studied experimentally and computationally. A possibility was proved that the second HEM1 passband can be moved above the accelerating frequency and that the value of R/Q can be increased by 60 % compared to that of the shunt impedance optimized DAW cavity, if one makes a compromise with 80 % of the optimized shunt impedance. The transverse coupling impedance of the second HEM1 mode at ¿ phase shift is less than 1 Mohm/m for a single cell, which is small by more than an order of magnitude compared to that of the re-entrant cavity or disk loaded cavity.