Three-dimensional evaluation of energy extraction in output cavities of klystron amplifiers

An accurate three-dimensional analysis of the performance of output gaps in klystron amplifiers was carried out. The parameters investigated were: beam radius, perveance, output gap angle, output gap peak voltage, RF phase, magnetic field, and beam interception. A new, accurate method for computing space-charge forces between axially and radially deformable rings was developed. Rigorous expressions for electric and magnetic fields in the tunnel and the gap were used. The highest computed efficiency for an optimally bunched beam was 80.3 percent with 6 percent "ideal" interception. An important conclusion is that efficiency decreases with increasing normalized tunned radius for constant in the examined range and probably beyond. Excellent correlation in efficiency and interception between a model klystron developed by E. Lien of Varian and the authors\´ program was established.