RIKEN/SPring-8, Hyogo
JASRI/SPring-8, Hyogo-ken
An 8-GeV C-band (5712 MHz) accelerator is employed as a main accelerator for XFEL/SPring-8. Since a C-band accelerating structure generates a high accelerating gradient of higher than 35 MV/m, the total length of the accelerator fits within 400 m, including the injector and three bunch compressors. We use 64 C-band rf units, which consist of 128 accelerating structures, 64 rf pulse compressors and waveguide components, 64 klystrons and modulators, etc. Mass-production of the C-band rf components has been done by several Japanese manufacturers. The components reliability has been improved during the production, and all the components finally have excellent quality. The production quality was also confirmed by a high power rf test. We achieved the accelerating gradient of 40 MV/m without any problem. Since XFEL realizes high bunch compression with precise control of the energy chirp, the rf should be quite stable. We developed a high precision high voltage charger combined with a low-noise klystron modulator. The pulse-to-pulse stability of the PFN voltage was less than 0.01%. Installation of the components started in August 2009 and was now almost completed on schedule.
RIKEN/SPring-8, Hyogo
JASRI/SPring-8, Hyogo-ken
A pump-probe experiment at XFEL/SPring-8 is one of the most prominent parts to extract the future of a coherent short-pulse X-ray laser. A commercial Ti:Sapphire mode-locked laser is presently used as a pump laser, while a probe laser is the XFEL. However, the time jitter of the commercial mode locked laser, as which is caused by the noise of an electrical mode-locking circuit, is around several hundred femto-seconds. This jitter value is not sufficient for a temporal resolution requirement of our pump-probe experiment with a laser pulse width of several ten femto-seconds. To improve this time jitter, the method, using a 770 nm Ti:Sapphire laser amplifiers directly triggered by a 1540 nm master optical oscillator as a time reference signal source for an XFEL accelerator, was devised. This method could eliminate the noise caused by the electrical mode-locking circuit. The basic principle of the method was proved by a preliminary experiment with laser pulse manipulation employing an E/O crystal shutter with a several ten ps response. This presentation describes a basic idea of this pump–probe method, a preliminary experiment set-up to check its feasibility, and experiment results.