Design Study of a Superconducting Deflecting Cavity

The superconducting RF beam separator now being constructed at Karlsruhe requires two 3m-long niobium deflectors, which are capable of operating with an equivalent deflecting field of at least 2 MV/m corresponding to an RF peak field of about 250 G. At present, a series of uniform periodic n/2-mode structures are investigated to determine a suitable fabrication technique, but it is anticipated to build the final deflector with a bi-periodic ¿/2-mode structure. The problem of mechanical tolerances is analysed by means of equivalent circuits. Questions which arise in connection with the coupling system, frequency tuner, end cells, joints, and mode stabilizers are discussed. Measurements on a test structure yielded a residual quality factor of Q¿109 and a peak field of ¿200 G after firing the cavity at 1400°C in a vacuum furnace.