• S.M. Matsubara
  RIKEN/SPring-8, Hyogo
• A. Maekawa
  The University of Tokyo, Nuclear Professional School, Ibaraki-ken
• H. Tomizawa
  JASRI/SPring-8, Hyogo-ken

High-brightness electron bunches are required with low slice emittance and bunch length of 30 fs (FWHM) in a targeting lasing part for XFEL/Spring-8. In order to obtain maximum brightness, it is very important to measure 3D bunch charge distribution (BCD) in real-time for future X-ray light sources (XFEL, ERL, etc). Therefore, we are developing a single-shot, non-destructive, and real-time 3D-BCD monitor based on Electro-Optical Sampling with a manner of spectral decoding. The monitor system requires for a probe laser source to realize a higher temporal resolution. The laser source has broad spectrum of over 400 nm width and a linear-chirp of over 3,000 fs² to be few-ps pulse duration. Then, the shape in the frequency regions is rectangular. The liner-chirp is supplied by using a broadband AO-modulator (DAZZLER) which is possible to remove higher order dispersions. The laser pulses will be amplified to be micro-joule pulse-energy with a manner of NOPA. The laser source with such as the properties is mentioned in this report. We expect the feasibility of 20 fs temporal resolution by using this laser source with an organic crystal such as a DAST crystal.

• A. Mizuno, H. Dewa, H. Hanaki, T. Taniuchi, H. Tomizawa
  JASRI/SPring-8, Hyogo-ken

Generally, vertical and horizontal emittance asymmetry has recognized as one of the problem of the high brightness, low emittance electron source like photo-cathode RF gun. As for the SPring-8 photo-cathode RF gun, the asymmetry also exists, the vertical emittance is always bigger than the horizontal one. We have been tackled this problem for several years and been eliminated some causes. Though, the asymmetry still remained. We calculated 3D electro-magnetic fields data of S-band traveling accelerator structure by MW STUDIO and calculated emittance by self-made 3D particle tracking code using these data. As a result, radial displacement of the magnetic field from mechanical center in a coupler cell of the accelerator structure is turned out to be one of the cause of these asymmetry. Though a slice emittance in the bunch keep constant, projected emittance of the whole bunch becomes worse in the coupler cell, since the fields' displacement effect on the each slice emittance is changed with rf time evolution. In the paper, we show simulation results and comparative discussion with experimental results.

• H. Dewa, T. Asaka, H. Hanaki, T. Kobayashi, A. Mizuno, S. Suzuki, T. Taniuchi, H. Tomizawa, K. Yanagida
  JASRI/SPring-8, Hyogo-ken

The synchronous technologies of RF signal and laser pulse is important for photo-cathode RF gun system, because it determines the beam stability in phase and energy. For time jitter as small as 300 fs between RF signal and laser pulse, laser driven RF generation has been developed for our synchronization system since 2002. In the system, RF signal is directly generated from the laser pulse of 89.25 MHz by filtering the output of the photo detector with a band pass filter of 2856 MHz. The remaining problem was that the amplitude of the RF signal linearly depended on the laser pulse amplitude. For this reason, there was some amplitude jitter in the generated RF signal, which might also cause time jitter. To reduce the amplitude jitter, we developed a new laser driven RF generation system with amplitude stabilization realized by saturation amplifiers. The RMS deviation of the RF amplitude could be decreased to 0.173 % from 1.18 %. The RMS time jitter measured with a sampling oscilloscope was so small that it could not be correctly measured. The whole triggering and RF system of Spring-8 RF-gun is also presented.