Test Results from Coaxial Cavities for Separated-Orbit Cyclotrons

Three different accelerating cavities were tested at ORNL for possible use in separated-orbit cyclotrons (SOC). All cavities were operated at about 49.2 MHz and at, or above, design power levels. The largest of these cavities is a prototype for a 10-to 50-MeV proton SOC having a total of 15 beam holes and a maximum accelerating voltage of about 290 kV. In cross-section, the prototype is a wedge-shaped coaxial line. Its overall width is about 230 in.; its height, 82 in.; and the maximum thickness, 67 in. Four tuners are located in the top of the cavity, opposite the open end of the center stub, for adjusting the cavity frequency and voltage distribution. The cavity was operated at various power levels up to a maximum of 66 kW. At this power input, the X-radiation near the cavity increased markedly with increasing power input. Some difficulty was encountered with multipacting, but the problem diminished steadily with operating time. The other two cavities that have been tested will be used in the Separated-Orbit Cyclotron Experiment (SOCE). One of the cavities is for use in the cyclotron and the other will be used in the injector. Both cavities were operated under vacuum and at power levels in excess of that required.