Temperature compensation of periodic permanent-magnet assemblies for focusing traveling-wave tubes

A major problem in the application of lightweight traveling-wave tubes focused by means of periodic permanent-magnet assemblies has been poor performance at extremes of ambient temperatures. Currently, operation of such traveling-wave-tube amplifiers is limited to a 50°C temperature because the magnetic field changes as the temperature of the barium-ferrite ceramic magnets varies. This paper describes techniques which can be used to maintain a constant magnetic field despite relatively large changes in ambient temperature.