High efficiency klystrons are becoming a subject of very strong interest for future particle accelerator systems. In this presentation we propose a new klystron concept at X-band able to reach more than 70 % efficiency with standard perveance values. This novel idea is based on a particular bunching process which uses a large number of cavities and short drift tubes. This innovative feature produces a so-called “quasi-adiabatic” bunching process and allows minimizing the velocity spread of the beam in the output cavity.
Different bunching structure designs and 1D large signal simulation results will be presented. Benchmarking of 2D/3D beam dynamic codes able to simulate the full behavior of the beam will also be shown. A development plan and possible alternatives to go towards a first prototype klystron will be finally proposed.