Production of ultra-short bunches employing alpha magnet and off-crest acceleration for coherent THz light sources

We have studied production of the very short electron beam to generate intense coherent THz radiation. Since the power of coherent synchrotron radiation is proportional to the bunch form factor, the bunch length shorter than 100 fs has to be produced to obtain large form factor sufficient to generated intense coherent THz radiation. The beam from the thermionic RF gun is injected into a bunch compression system consist of an alpha magnet and a linac employing velocity bunching. We report the bunch compression scheme of this system. (author)