Magnetic field profiles in depressed collector region for small-orbit gyrotrons with axial or radially extracted spent beam

Feasibility studies for the design of multiple depressed collectors for small-orbit gyrotrons are presented. Particular attention is paid to the effect of profiles of magnetic field on the electron trajectories. Two cases are considered involving alternative approaches to separating the paths of the spent beam and the output radiation. In the first example the beam proceeds axially while the radiation is coupled out radially. A magnetic field profile that is neither purely adiabatic nor purely non-adiabatic is shown to give energy sorting and collection of beamlets without reflection of the particles, while keeping the outermost radius of the collector within reasonable limits. Studies are also presented of electron trajectories of a radially directed beam in the collector region. It is seen that the magnetic field must have a very low value and its configuration must be tailored over a wide region, A magnetic circuit consisting of a shield and a number of independently controlled coils is described which can produce such a field configuration. Results of trajectory tracing are presented showing energy sorting and collection without reflection.