A COMPACT FEL UP-CONVERTER OF COHERENT RADIATION

The objective is to generate a powerful millimeter-wave FEL signal in a single pass, using a coherent microwave source (24 GHz) to prebunch the electron beam for a harmonically-related wave (72 GHz); one would obtain a millimeter wave source which is phase-referenced to a coheren t laboratory source. We use the Columbia FEL facility, operating the e lectron beam at 600 kV, 100 A; undulator period = 1.85 cm and 200 G (K = 0.2); electron beam diameter = 3 mm inside an 8.5 mm ID drift tube; guiding field of 8800 G. Under these conditions, both the microwave s ignal (5 kW input) and the millimeter signal will show travelling-wave gain in the TE11 mode. We report initial experimental results for the millimeter wave spectrum and find an overall power gain of similar to 20 for the 24 GHz input wave. Also presented are numerical solutions of the wave growth using the FEL equations with slippage.