Modeling thermal beam effects in coupled cavity TWTs

Summary form only given. Successful design and optimization of coupled cavity TWTs (CC-TWTs) operating in the mm and sub-mm wavelength range requires adequate simulation tools capable of including many details of the beam-wave interaction for realistic beams. In particular, the designs of CC-TWTs require taking into account effects of the finite emittance of the electron beam used in the device. The 2.5D large-signal code TESLA-CC [1] is capable of accurate modeling of CC-TWTs with different beam injection models, including beams imported from the collector/gun design code MICHELLE [2]. The typical number of particles included in the electron gun simulations by MICHELLE can be a few thousands for a cold beam; taking into account “thermal” beam effects will require increasing this number even more to allow proper statistics. Although the direct use of such a large number of particles by TESLA-CC is possible, it is desirable to depopulate the given set of particles without loosing valuable information about the beam particles´ distribution. A new depopulation algorithm has been introduced in TESLA-CC to create a beam distribution using a reasonable number of particles that accurately represent the “thermal” beam distribution prepared by MICHELLE. The algorithm is based on correlation analysis of MICHELLE data and generation of a two-dimensional distribution function, taking into account an arbitrary level of correlation between components of the electrons´ transverse velocities. Results of this algorithm are used to perform detailed simulations to find impact of the “thermal” effects on a predicted performance of coupled cavity TWTs.