Low voltage FEL amplification based on a longitudinal interaction mechanism

Summary form only given. A parallel approach to reduce the size of suitable FEL drivers is to minimize the electron voltage necessary for a strong FEL radiation of a given frequency. The main thrusts are at present to employ either slow-wave waveguiding structures or microwiggler magnets. In this contribution, we consider an alternative approach based on the interaction between the longitudinal component of the electrons´ undulating motion and the longitudinal electric field of TM modes of the waveguide electromagnetic wave. A small signal analysis is presented to study the longitudinal interaction mechanism in a FEL amplifier consisting of a circular waveguide and a planar wiggler magnet. It is shown that as the longitudinal component of the electron undulating motion varies at a period half as long as the wiggler period, /spl lambda//sub w/, the electron beam involved in the longitudinal interaction experiences an effective wiggler magnet of 0.5/spl lambda//sub w/. Therefore for a FEL based on the longitudinal interaction mechanism, the required electron voltage for a FEL radiation at a given frequency is less than that for a FEL based on the usual transverse interaction mechanism. Detailed characteristics of the longitudinal FEL interaction mechanism is illustrated with system designs.