Materials and machining processes for 140 GHz gyrotron resonators

Excess heating of the high power gyrotron resonator due to ohmic losses may cause irreversible changes of the resonator geometry. Thus the oscillating frequency is shifted and multimoding may be difficult to be prevented. The following questions have been examined in order to support the construction of a TE03 gyrotron resonator at 140 GHz: Do harder copper alloys have any advantages? How do wall losses depend on the manufacturing process? The paper presents the measured surface resistances of oxigene free copper and different copper alloys. These materials have been machined with different processes. The surface resistance is determined by measuring the Q-factor of a cylindrical cavity at 143 GHz.