Large Signal Klystron Simulation

Summary form only given. L-3 uses several advanced computational codes for design and analysis of klystron RF performance. This paper presents recent results from two of these: the large signal codes, TESLA and MAGIC 3D. TESLA, developed by the Naval Research Laboratory and SAIC, is quasi-3D, that is, it calculates the 3D electron trajectories for axisymmetric RF structure geometries. MAGIC 3D, from ATK-Mission Research, is a particle-in-cell code allowing arbitrary 3D geometries. TESLA is used to model a four cavity CW production klystron. RF loss, incorporated in one of the gain cavities to lower the quality factor and broaden bandwidth, was included in the model. TESLA accurately predicted both small signal gain and saturated output power. TESLA was also used to study the effect of dimensional tolerances on output power and the results have been confirmed by experiment. To model more complex klystrons, a combination of codes is used. The RF gain section is simulated using a ID or ID code. The modulated beam is then exported into a 3D code which is required to correctly model the asymmetric output circuit geometry. This technique has been used to predict the RF performance of one of L-3´s wide instantaneous bandwidth klystrons. The RF gain section, comprised of several cavities incorporating varying degrees of RF loss, was modeled with MAGIC ID. The modulated beam was then exported into a MAGIC 3D model of the extended interaction output circuit, consisting of two inductively coupled cavities, the second loaded by the output waveguide. Simulation results are compared to measured data