SIMULATION OF AN ANNULAR BEAM FREE-ELECTRON LASER

A nonlinear analysis of an annular beam FEL with a helical wiggler and axial guide field is presented. An annular beam has the advantage of reduced DC self-fields, facilitating beam transport in short period wi gglers. A 55 kV/5 A annular beam interacting with the TE(11) cylindric al waveguide mode is considered. The inner and outer beam radii are 0. 27 and 0.33 cm, respectively. The wiggler amplitude is 250 G and the p eriod is 0.9 cm. Axial guide fields up to 3 kG are studied. The ARACHN E slow-time-scale simulation code shows that efficiencies of 10%, corr esponding to gains >40 dB, are possible for grazing incidence with the TE(11) mode in Ku-band. In addition, the 3 dB instantaneous bandwidth is found to be greater than 20%.