Refocusing of the spent axisymmetric beam in klystron tubes

Analytic methods were developed and employed to optimize the magnetic field transition region between the output interaction gap of a klystron and a multi-stage depressed potential electrostatic beam collector, in order to enhance the power conversion efficiency of satellite-borne broadcast transmitters. Permanent magnet structures were designed to provide the magnetic field distributions required to expand and recollimate the spent electron beam of the power amplifier klystron for proper entry into the beam collector. These design criteria for magnetic field distributions for expanding and recollimating spent-beam electrons for optimal entry into a multi-stage depressed potential collector are generally applicable to traveling-wave tubes as well as klystrons.