Simulation of Klystrons With Slow and Reflected Electrons Using Large-Signal Code TESLA

The problem of modeling slow and reflected electrons that appear during operation of high-power klystrons is discussed. These electrons are not only problematic for the operation of real klystrons but also present a numerical challenge for simulation codes that solve the equations of motion with axial distance rather than time as the independent parameter. To meet this challenge, particles with axial velocity below some threshold are treated using an alternative algorithm. This approach has been implemented in the simulation code TESLA. The method is verified by comparison with PIC simulation. The effect of these particles on the efficiency of a hypothetical device is also presented.