First lasing of a Cherenkov free-electron laser with annular electron beam

A Cherenkov FEL with an annular electron beam has been succesfully operated , During the first lasing experiments output was found for accelerating vol tages ranging from 85 to 150 kV and currents from 1 to 10 A. At a particula r accelerating voltage lasing was observed for several distinct settings of the magnetic field (0.7-1.6 T). This field is used to compress and guide t he electron beam along the dielectric liner. Depending on the magnetic fiel d setting, the output was reproducible or showed large fluctuations within a single laser pulse as well as from pulse to pulse. Due to a misalignment of the cathode the total output power is only of the order of 100 W. From t heoretical considerations the spectrum is expected to center around 19 GHz. (C) 1999 Elsevier Science B.V. All rights reserved.