ELECTRON-BEAM QUALITY LIMITATIONS AND BEAM CONDITIONING IN FREE-ELECTRON LASERS

Free electron lasers (FELs) operate over a large portion of the electr omagnetic spectrum, i.e. from the mu-wave to the UV. At the high frequ ency end of the spectrum, FEL operation is severely limited by a numbe r of factors; prominent among them is the electron beam quality (elect ron axial velocity spread). The axial velocity spread is due to the el ectron beam's intrinsic energy spread and emittance. The general wavel ength limitation in FELs due to electron beam quality is discussed. A method for reducing the axial velocity spread is proposed and analysed . This beam conditioning method redistributes the electrons' energy ac cording to their betatron amplitude. This is accomplished by interacti ng the beam with an axially symmetric, slow, TM waveguide mode.