Generation and application of a subpicosecond high brightness electron single bunch at the S-band linear accelerator

Abstract

A subpicosecond 37‐MeV electron single bunch was generated at the S‐band linear accelerator of the Nuclear Engineering Research Laboratory, University of Tokyo. An original single bunch with a pulse width (FWHM) of less than 10 picoseconds was successfully compressed to a subpicosecond time domain by achromatic magnetic pulse compression. The energy modulation was optimally matched to the magnetic optics to achieve the most effective compression by tuning RF power and phase of the microwave. A femtosecond streak camera with a time resolution of 200 fs was used to measure the pulse shape of electron bunches by one shot via Cherenkov radiation emitted by the electrons in air. The specification of optical components was also optimized to avoid pulse broadening due to optical dispersion. Finally, the shortest pulse width in FWHM is 0.7ps in the best operating mode. The compressed bunch has an electric charge of 1 nC (6.2×109 electrons) on average. The subpicosecond electron single bunch will be utilized for exploration of ultrafast and fundamental radiation physics and chemistry. As the next project, we propose a femtosecond ultrafast quantum phenomena research facility where both 100‐fs electron and laser pulses will be available. Especially, an X‐band (11.424‐GHz) femtosecond electron linac is under design.