Use of Ferrite-50 to strongly damp higher order modes

A new higher order mode damping concept has been proposed for use with the superconducting RF cavities for the Cornell B-factory, CESR-B. All higher order modes are brought out of the cavity via the beam tubes which have a large diameter and special shape. Because of their propagation, these modes can be damped by a 15 cm long beam tube section of Ferrite-50 such that the Q-s of all the modes are below 200, with most being below 100. The microwave losses of Ferrite-50 have been found to be ≥ 104 times higher than copper at ∼1 GHz, and to decrease by a factor of 10 at 10 GHz. The tolerance of Ferrite-50 to high power has been tested up to 10 watts/cm2 (RMS). It vacuum properties appear promising and a 200C bake is permissible without a loss of its microwave absorptive properties. Techniques by which to fabricate a 24 cm diameter beam tube section are being explored