Design of Modified Wiggler for Higher Harmonic Lasing of Free Electron Laser

To improve the harmonic gain of Free Electron Laser (FEL), we have developed a wiggler having a harmonic wiggler field. We call such a wiggler the "modified wiggler". The modified wiggler consists of a conventional planar wiggler and high-permeability shims. Owing to the simplicity of design, we can develop wigglers having various types of modified fields, easily and economically. We show the design basis for the modified wiggler. Then, we develop a modified wiggler for 5th-harmonic generation.