Free electron maser amplifier energy recovery experiments

We present results from a reversed guide magnetic field Raman free electron maser (FEM) amplifier experiment at Strathclyde University. The FEM amplifier is designed for a near grazing intersection of the beam line and waveguide mode to maximise the frequency tuning range. The tuneability is further extended by adjustment of beam voltage and undulator field strength. The FEM amplifier has shown a gain of over 35 dB over a 30% frequency band. The frequency range of operation can be extended to 65% of centre frequency by adjustment of the cathode voltage. Saturated gain of 23 dB with an output power of 1 MW and efficiency of 5% has been measured. An experiment is currently under way to increase the overall efficiency of the device using a two stage depressed collector energy recovery system.