Study of Dynamic After Cavity Interaction in Gyrotrons-Part II: Influence of a Nonuniform Magnetic Field

Spurious oscillations, particularly dynamic after cavity interaction (ACI) in high-power gyrotrons gained attention as an influencing factor on the overall gyrotron performance. Numerical investigations are a main pillar for a deeper understanding of this phenomenon. The Karlsruhe Institute of Technology in-house self-consistent, time-dependent self-consistent multimode code was modified to accommodate the influence of an axial variation of the external magnetic field on the after cavity dynamics. Inclusion of the influence of the nonuniform distribution of the magnetic field in the time-dependent gyrotron beam-wave interaction differential equations is necessary to make proper numerical investigations in terms of the appearance of the dynamic ACI particularly in the output waveguide section (uptaper), where the nonuniform distribution of the magnetic field is more significant. We evaluate the importance of this for modeling of three different high-power gyrotron cavities, where partially undesired weak interactions in the up-taper/launcher region have been observed.