Inagaki, T.

Paper	Title	Page
THPPH043	Stable RF Phase Insensitive to the Modulator Voltage Fluctuation of the C-band Main Linac for SCSS XFEL	684
	J.-S. Oh, T. Hara, T. Inagaki, J.-S. Oh, T. Shintake, K. Shirasawa RIKEN Spring-8 Harima, Hyogo
	The SCSS (SPring-8 Compact SASE Source) XFEL requires extremely stable RF system in both amplitude and phase. The fluctuation of RF output is mainly caused by modulation of the klystron beam-voltage pulse, which is directly governed by the charging stability of a klystron modulator. During R&D study on beam stability, we found a special operation point, where the beam energy gain is insensitive to the modulator voltage fluctuation. This phase can cancel out the both fluctuations and provide constant accelerating field. The stable phase depends on the klystron parameters such as the length of drift tube, operating voltage, efficiency. It is about 9 degree in case of the C-band main linac for SCSS XFEL. The bunch length after bunch compressor is so short that additional longitudinal energy spread due to the RF curvature is about 5% of the one caused by the longitudinal wake field. The particle energy is high enough so that longitudinal defocusing is negligible. The reduction of beam energy due to off-crest acceleration is less than 2%. This paper shows the analytical relation of the stable phase. ELEGANT simulation shows no appreciable degradation of the slice parameters.
THPPH044	Analysis of Inverter Charging Waveform for Ultra Stable SCSS Modulator	688
	J.-S. Oh, T. Inagaki, J.-S. Oh, T. Shintake, K. Shirasawa RIKEN Spring-8 Harima, Hyogo
	The SCSS (SPring-8 Compact SASE Source) XFEL requires ultra stable RF sources. The SCSS uses normal conducting technology for beam acceleration, in which pulse-to-pulse power fluctuation in RF-system dominates beam stability. The SCSS smart modulator uses an inverter charging system. Therefore, the inverter is responsible to RF stability, which means that we need an ultra stable charging power supply. In order to stabilize the charging level, we need a clean and stable feedback signal of the charging voltage. There are not only pulse forming network (PFN) capacitors but also protective series resistors and distributed reactive components of a pulse transformer and a klystron load in the charging path. Therefore, the charging waveform becomes somewhat complicated. In addition, improper conditioning of monitoring signal can easily degrade the charging stability. The understanding of the charging waveform and the proper conditioning of feedback signal is essential to realize such an ultra stable charging performance. This paper shows the detail analysis of the charging waveform of SCSS modulators and the stability dependency on the signal conditioning.
THCAU02	Low Emittance Injector at SCSS	769
	T. Shintake, T. Hara, A. Higashiya, T. Inagaki, H. Maesaka, Y. Otake, K. Shirasawa, T. Tanaka, K. Togawa, M. Yabashi RIKEN Spring-8 Harima, Hyogo H. Baba, K. Onoe, H. Tanaka JASRI/SPring-8, Hyogo-ken H. Matsumoto KEK, Ibaraki T. Tanikawa University of Hyogo, Hyogo
	In order to realize X-ray FEL at 1 A wavelength, it is required to generate low emittance beam with high peak power. Typically 1 π-mm-mrad, and 2~4 kA beam has to obtained at undulator line. In SCSS: SPring-8 Compact SASE Source, we decided to use thermionic cathode and velocity bunching process rather than the rf-gun with photo-cathode. To verify our principle and hardwares, we constructed a test accelerator, 250 MeV, 60 nm FEL. The author reports experimental results of the test accelerator.
	Slides
	Talk