TESLA: large signal simulation code for klystrons

Summary form only given. TESLA (telegraphist's equations solution for linear beam amplifiers) is an example of hybrid code designed to simulate linear beam vacuum electronic devices with cavities, such as klystrons, extended interaction klystrons, twystrons, and coupled cavity amplifiers. The model includes a self-consistent, nonlinear solution of the 3D electron equations of motion and the solution of time-dependent field equations. The model differs from the conventional particle in cell approach in that the field spectrum is assumed to consist of a carrier frequency and its harmonics with slowly varying envelopes. The main numerical problem in the simulation of high gain klystrons is the artificially low decay rate of cavity fields when the resonant frequency of the cavity is far from the carrier frequency. A second problem found in high power klystron simulations is the presence of strongly decelerated, and even stopped or reflected, particles in the output resonator. This paper described modifications to TESLA to overcome these problems.