Double-decker electron beam accelerator and pulse radiolysis

A new concept of double-decker electron beam accelerator is proposed to study the ultra-fast electron-induced reactions in materials by pulse radiolysis. The double-decker electron beams are generated and accelerated in an S-band linear accelerator with different positions in vertical direction and a time delay. One of them is used as a pump electron source and another is converted to light as a probe light source. The time jitter between the pump electron beam and the probe light is thus reduced. The time resolution of pulse radiolysis is expected to be improved. The double-decker electron beam has been generated successfully by injected two laser beam into the photocathode RF gun, which is generated by splitting an Nd:YLF picosecond laser beam. The double-decker electron beams were accelerated up to 31 MeV by an S-band booster linear accelerator and compressed into femtosecond by a magnetic bunch compressor. 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 emittance was obtained to be 3.3 mm-mrad for the upper beam and 6.4 mm-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. The Cherenkov light generated in a suprasil plate and OTR produced on a mirror from the electron beam were also measured. (author)