Permanent magnet study for high average power TWTS

The average power capability of permanent magnet focused high power linear beam tubes is typically limited by beam interception resulting from beam defocusing with large signals. This is prevented in solenoid focused tubes by using fields substantially higher than the Brillouin value. This method of confining the beam is only practical in periodic magnetic geometries for relatively low values of beam perveance. Size and weight advantages of permanent magnets over electromagnets and their accompanying power supplies make it advantageous to find ways for increasing the average power handling capability of tubes with permanent magnet configurations. In instances where lower perveance beams continue to interact at acceptable RF levels, substantial improvements in beam defocusing are indicated, but at the penalty of higher operating voltages for similar power levels. A detailed thermal analysis of a typical high power traveling wave tube (TWT) indicates areas where additional thermal capability might be achieved. A system life cycle analysis on a solenoid focused tube indicates a small percentage of failures due to focusing problems, however, failure rates associated with the tube alone would be higher. A design is presented for a high average power S-Band TWT using concepts developed during the study.