Ultrashort Electron Beam Pulses and Diagnosis by Advanced Linear Accelerators

Abstract

240fs 18 MeV low emittance(6 pai mm.mrad) electron beam was generated and its pulse shape was diagnosed by the S‐band laser photocathode RF gun and linac. The maximum charge per bunch was 7 nC. This electron pulse was synchronized with 100fs 0.3TW Ti:Sapphire laser with the timing jitter of 330fs(rms). Recently, the Cu cathode(QE10∧‐4) was replaced by Mg cathode(QE10∧‐3). This system is utilized for radiation chemistry analysis for supercritical water. We have adopted the four diagnostic methods(femtosecond streak camera, coherent transition radiation interferometer, far‐infrared polychromator, fluctuation method) and checked their time‐resolution precisely. Further, we are doing the experiment on laser plasma cathode by 12TW 50fs laser and He gas jet. Laser plasma wakefield acceleration and electron injection via wavebreaking are planned. We have developed a new theory of self‐injection scheme to generate ∼10fs electron pulse. We have already succeeded in observing 40 MeV low emittance electron beam of 14 nC.