Magnetic-field source for bichambered electron-beam devices

Some electron-beam devices such as gyro amplifiers are composed of tandem coaxial chambers with different uniform axial magnetic fields in their interiors. Therefore, there is a step in the field profile in the vicinity of the juncture of the two chambers, which are sometimes of different diameter as well. An electric solenoid is usually employed to furnish such a field, but such sources are bulky, cumbersome, and consumptive of energy, and usually provide only rough approximations to the ideal field profile. This paper describes a permanent magnet field source that provides a constant axial field of 2.0 kOe in the larger of the two chambers and 0.5 kOe in the smaller. The basic field is provided by tandem permanent magnet solenoids. The rather broad transition between the field values in the two chambers is considerably narrowed (40%) by application of a radially magnetized ring to the juncture of the two solenoids. The field profile can be made to conform to that specified to within a few percent.