Performance of a cryogenic sapphire dielectric resonator

In this paper we present details of the design and operation of a cryogenic sapphire dielectric resonator. This includes controlling the resonator´s temperature to better than 90 μK and the effect of paramagnetic impurities on the predicted performance. We also discuss room temperature observations on the efficiency of the novel microwave choke arrangement. Finally we present some preliminary stability measurements for our Mark I system