AN ACCELERATOR WIGGLER FOR HIGH-EFFICIENCY FEL OPERATION

A possible approach to high efficiency FEL operation is to combine a m icrowave linear accelerator and magnetic wiggler into a single structu re. As the electrons lose energy to the radiation at the FEL oscillati on wavelength (e.g. 10 mum), energy is replaced by the microwave linac . The electron beam acts as a catalyst for the conversion of microwave power to infrared power. Several advantages to the accelerator/wiggle r are: it is possible to obtain high conversion efficiency in a short length; small-signal gain reduction can be avoided; power extraction m ay be increased by increasing length; there is little detrapping; and electron beam energy out of the wiggler is relatively monochromatic, p ermitting efficient energy recovery. A six period, full scale model of the accelerator/wiggler has been fabricated to check the computer sim ulations for both microwave and magnetic properties. Microwave measure ments on this model indicate that the predicted Q is accurate, that th ere is an approximate 1.5% error in the predicted resonant frequency a nd that critical coupling to the structure in the presence of the elec tron beam can be achieved with a direct, rectangular waveguide feed.