A SUPERRADIANT FEL EXPERIMENT WITH AN ANNULAR ELECTRON BEAM

A free-electron laser (FEL) superradiant amplifier experiment is described,in which an annular electron beam is generated by the EPA-74 pulse-line accelerator.The voltage of diode ranges between 400kV and 700kV.The graphite annular cathode of a fo-illes diode has a 3cm O D.and 2.8 cm I.D..An annular electron beam of 1 kA is guided into the interaction region by a high axial magnetic field.The cylindrical hollow electron beam has a 4cm diameter and a wall thickness of 1mm,and propagates through a drift tube of 5.2cm 1.D..The electrons have low transverse velocities before injected into the interaction region.The interaction region consists of a 22-period pulsed bifilar helical wiggler (λw=2 cm) with adiabatic entrance and exit.A 10MW radiation has been observed at 32GHz frequency representing a 1.6% efficiency.Measurements of the dependence of radiation output power upon the length of interaction region show a grow in rate of 2dB/cm.Spectral diagnoses are performed with the 8mm waveguidedis-persive line and hand-pass filters.Radiations in the frequency range of 27-38GHz are measured while changing the energy or and the magnetic field amplitude.The results consist with calculations on the basis of the guiding centre approximation methode.