Development of Double-decker Electron Beam Accelerator for Femto/attosecond Pulse Radiolysis

A concept of double-decker electron beams, which have vertically different positions and time delay, was proposed for study of ultra-fast electron-induced reactions or phenomena by pulse radiolysis technique. One of the double-decker electron beams is used as a pump source, and another is converted to Cherenkov light and used as a probe light source. The double-decker electron beams were generated successfully by injecting two Nd:YLF picosecond laser beams into a photocathode RF gun. The beams were accelerated up to 31MeV by an S-band booster linear accelerator and compressed by a magnetic bunch compressor into femtosecond. The profiles of the double-decker electron beams were measured at the exits of the RF gun, the linac and the bunch compressor. The normalized transverse emittances of both beams were obtained to be 3.3mm-mrad for the upper beam and 6.4mm-mrad for the lower beam at bunch charge of 2nC. The relative energy spread was obtained to be 0.1~0.2% for both beams.