Modelling of Klystrons with Reflected Electrons Using the Large-Signal Code TESLA

The appearance of reflected electrons in a standard klystron amplifier is a well-known phenomena, which can result in problems for the device's operation, including: 1) damage and heating of the cathode and the walls; 2) drops in efficiency; 3) unstable oscillations due to the feedback. The reasons for particle reflection include the desire to operate in a high efficiency regime, or in the case of multiple beam devices, variations in R/Q values from beamlet to beamlet. It is important to have a tool that can predict the appearance of reflected electrons and model their behaviour in a device.To study oscillations induced by signal feedback by reflected particles we created a configuration in which particles reflected in the output cavity travel back to previous cavities. Here we present our preliminary results for this configuration. Our work complements a previous study modelled using a PIC code.