Ohshima, T.

Paper	Title	Page
TUPC143	Precise RF Control System of the SCSS Test Accelerator	1404
	H. Maesaka, T. Fukui, N. Hosoda, T. Inagaki, T. Ohshima, Y. Otake, H. Tanaka RIKEN/SPring-8, Hyogo T. Hasegawa, S. Takahashi, S. Tanaka JASRI/SPring-8, Hyogo-ken M. K. Kitamura NDS, OSAKA
	We present the development and performance of the low level rf control system of SCSS test accelerator (VUV-FEL facility). The FEL radiation in the wavelength region of 50-60 nm reached saturation in fall 2007. Since then, the FEL intensity fluctuation has been suppressed within 10%. This performance was achieved by stabilizing the rf phase and amplitude of the accelerator. For example, the rf phase stability of the 238 MHz cavity is achieved to be 0.03 degree rms corresponding to 350 fs. Those of other cavities such as C-band (5712MHz) accelerator are also obtained to be several 100 fs. To control the rf phase and amplitude precisely, we have developed an IQ modulator / demodulator system. To treat the baseband signal of the system, we have also developed VME high speed DAC / ADC boards. The phase skew of the IQ system is ± 1.0 degree without correction and ± 0.1 degree after correction. To suppress the slow drift of rf components, we applied a PID feedback control loop to the rf source and cavity system. We also improved temperature stabilization for the acceleration structures.
WEPC076	Remote Tilt-control System of Injection Bump Magnet in the SPring-8 Storage Ring	2172
	K. Fukami, C. Mitsuda, M. Oishi, M. Shoji, K. Soutome, H. Yonehara, C. Zhang JASRI/SPring-8, Hyogo-ken M. Hasegawa, T. Nakanishi SES, Hyogo-pref. T. Ohshima RIKEN/SPring-8, Hyogo
	The SPring-8 storage ring has four pulse-bump magnets to generate bump orbit for beam injection. Rotational error of the bump magnets around a beam-axis (tilt) induces the stored-beam oscillation in vertical direction due to horizontal error field. In the top-up operation, vertical perturbation of the stored-beam during beam injection is mainly produced by the tilt. We evaluated the tilt angle by measuring of the perturbation turn-by-turn using a single-pass BPM system and realigned bump magnets manually inside the accelerator tunnel. It was required to repeat the measurement and realignment processes two or three times for convergence. To correct the tilts smoothly, we developed a remote tilt-control system. The system consists of two fixed and one movable supports in vertical direction under each bump magnets. The movable support is driven by a stepper motor through 1/30 worm gear in the range of ±4 mrad with the accuracy of less than 0.1 mrad. By using this system, we succeeded complete on-beam reduction of the perturbation.
WEOAM01	Operation Status of the SCSS Test Accelerator: Continuous Saturation of SASE FEL at the Wavelength Range from ~50 to 60 nanometers	1944
	H. Tanaka, T. Fukui, T. Hara, A. Higashiya, N. Hosoda, T. Inagaki, S. I. Inoue, T. Ishikawa, H. Kitamura, M. K. Kitamura, H. Maesaka, M. Nagasono, T. Ohshima, Y. Otake, T. Sakurai, T. Shintake, K. Shirasawa, T. Tanaka, K. Togawa, M. Yabashi RIKEN/SPring-8, Hyogo T. Asaka, T. Hasegawa, H. Ohashi, S. Takahashi, S. Tanaka JASRI/SPring-8, Hyogo-ken T. Tanikawa RIKEN Spring-8 Harima, Hyogo
	The SPring-8 compact SASE source (SCSS) test accelerator for XFEL/SPring-8 was constructed in 2005. The first lasing at 49 nm, though not reached saturation, was observed with the 250-MeV electron beam in June 2006. Towards the saturation, we started stabilizing the RF system in the injector section, which dramatically stabilized the lasing condition. The stable operation enables us to tune each of the machine parameter precisely by using the lasing response. The second undulator, which did not sufficiently contribute to the first lasing because of large multipole field errors, was replaced by new one. These improvements led us to the successful observation of SASE saturation at the wavelength ranging from ~50 to 60 nm in September 2007. A pulse-energy of 30 uJ is routinely obtained at 60 nm. Analysis of the obtained SASE saturation data with a 3D-FEL simulation code, SIMPLEX, suggests that the electron beam emittance is almost unchanged through the bunch compression process. The stable and intense EUV SASE FEL has been offered for user experiments since October 2007. The achieved electron beam performance, lasing property as well as the latest analysis result will be presented.
	Slides
THPC127	Filling of High Current Singlet and Train of Low Bunch Current in SPring-8 Storage Ring	3284
	T. Nakamura, T. Fujita, K. Fukami, K. Kobayashi, C. Mitsuda, M. Oishi, S. Sasaki, M. Shoji, K. Soutome, M. Takao, Y. Taniuchi JASRI/SPring-8, Hyogo-ken T. Ohshima RIKEN/SPring-8, Hyogo Z. R. Zhou USTC/NSRL, Hefei, Anhui
	We performed the storage of high current singlet of 10mA/bunch and a train of bunches of 0.3mA/bunch under the bunch by bunch feedback systems with newly developed bunch current sensitive automatic attenuators with FPGA. The automatic attenuator reduces the signal level of the high current bunch by factor three to five to avoid the saturation of the feedback systems. With this system, the feedback systems suppress horizontal and vertical mode-coupling instabilities and raise the bunch current limit from 3.5mA/bunch to 12mA/bunch, and simultaneously the systems suppress the multi-bunch instabilities by resistive-wall and cavity higher order mode impedances. The improvement of the automatic attenuation system to fit to the final target of the bunch current in the train, 0.06mA/bunch, are being performed. The other problems which limit the filling patterns, such as saturation of the readout electronics of the beam position monitor system and the heating of vacuum components by high current bunches, will be briefly presented.