Design of a Wiggler - Focused , Sheet Beam X Band Klystron

An X band klystron using a sheet beam and wiggler focusing was simulated using the 2 + t dimensional particle in cell code MASK.’ Simulation of the rf cavities was by means of the port approximation used in modell ing of standard klystrons.2 The wigglers, which would need permanent magnets to achieve the required field strengths, were modelled using an idealized analytic expression with an exponential rise and a linear taper superimposed on a sinusoidal variation. Cavity locations and tunings were varied for maximum output power. Beam voltage and current were also varied to explore the effect on efficiency. Both an idealized laminar beam and a more realistic beam from a gun design code were studied. For a voltage of 200 kV and current of 20 amp per linear cm efficiencies of approximately 50% were calculated.