Strong coupling operation of a FEL amplifier with an axial magnetic field

This paper presents the results of a FEL experiment at 35 GHz, using a highly relativistic electron beam (T = 1.75 MeV). The electron pulse length is 30 ns FWHM with a peak current of 400 A. The FEL is designed to operate in the high-gain Compton regime, with a negative coupling parameter (Φ < 0) leading to a stong growth rate. More than 50 MW of RF power in the TE11 mode (43 dB gain) has been obtained with good reproducibility. The experimental results are in good agreement with predictions made using the 3D stationary simulation code SOLITUDE.