Shoji, M.

Paper	Title	Page
TUPLT074	Dark Current Reduction System for SPring-8 Linac	1324
	T. Kobayashi, T. Asaka, H. Hanaki, M. Shoji, S. Suzuki, K. Tamura JASRI/SPring-8, Hyogo
	The SPring-8 linac accelerates dark currents generated by its injector part up to 1 GeV. These dark currents are injected with main beam into the SPring-8 storage ring and then spoil the purity of the stored beam. The dark currents are mainly composed of a grid emission current from a thermionic gun and field emission currents from rf accelerating structures. A beam deflector for kicking only the grid emission by a pulsed electric field was developed and installed in the SPring-8 linac. We observed that the beam deflector greatly reduced the grid emission current accelerated up to 1 GeV. The measured purity of the stored single-bunched beam was about 5x10-6 when the deflector operated, which was almost 1/100 of the purity without filtering by the deflector. However, the deflector, which is installed before the prebucher, cannot reduced the field emission currents from the buncher cavities and the first acccelerating structure. These dark currents take considerable proportion of the total dark currents observed at the end of the linac. We are trying to spin off the field emission currents by weak magnetic fields across the accelerating structure generated by several coils.
THOACH03	Top-up Operation at SPring-8 - Towards Maximizing the Potential of a 3rd Generation Light Source	222
	H. Tanaka, T. Aoki, T. Asaka, S. Daté, K. Fukami, Y. Furukawa, H. Hanaki, N. Hosoda, T. Kobayashi, N. Kumagai, M. Masaki, T. Masuda, S. Matsui, A. Mizuno, T. Nakamura, T. Nakatani, T. Noda, T. Ohata, H. Ohkuma, T. Ohshima, M. Oishi, S. Sasaki, J. Schimizu, M. Shoji, K. Soutome, M. Suzuki, S. Suzuki, S. Takano, M. Takao, T. Takashima, H. Takebe, K. Tamura, R. Tanaka, T. Taniuchi, Y. Taniuchi, K. Tsumaki, A. Yamashita, K. Yanagida, H. Yonehara, T. Yorita JASRI/SPring-8, Hyogo M. Adachi, K. Kobayashi, M. Yoshioka SES, Hyogo-pref.
	Top-up operation maximizes research activities in a light source facility by an infinite beam lifetime and photon beam stability. We have been improving the SPring-8 accelerators to achieve the ideal top-up operation. For the perturbation-free injection, we adjusted the magnetic field shape of four bump magnets to close the bump orbit, and introduced a scheme to suppress the stored beam oscillation induced by the nonlinearlity of sextupole magnets. These reduced the horizontal oscillation down to a third of the stored beam size. For the loss-free injection, beam collimators were installed upstream of the injection line. This realized the injection efficiency of ~100% under the restricted gap condition of in-vacuum insertion devices (ID). Since autumn 2003, we have been injecting the beams keeping the photon beam shutters opened and ID gaps closed. We developed a bunch-by-bunch feedback system to reduce the beam loss further with all the ID gaps fully closed by lowering the operating chromaticity. The operation with constant stored current is scheduled in June 2004. We present the overview and progress of the SPring-8 top-up operation focusing on our developments and results.
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