IBIC2015 - List of Authors (Dewa, H.)

Paper	Title	Page
TUPB020	Long-Term Stability of the Beam Position Monitors at SPring-8	359
	T. Fujita, H. Dewa, M. Masaki, S. Matsubara, S. Sasaki, S. Takano JASRI/SPring-8, Hyogo-ken, Japan H. Maesaka, Y. Otake RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
	At the SPring-8 storage ring, the renewal of BPM electronics in 2006 has improved orbit feedback resolution . However, a stability issue of the whole BPM system, including the buttons, the cables and the electronics, remains to be settled for long-term stability of the beam orbit. The BPM in the present SPring-8 has gain imbalances among 4 electrode channels, which result in large offsets (~1 mm). The imbalances are routinely corrected in accordance with a beam-based measurement . But, the offset error increases close to 100 um during the operation, because of the imbalance fluctuations. Major origin of the imbalances is standing waves caused by reflections in BPM cables. As a countermeasure for the imbalance issue, isolators to mitigate the standing waves were equipped. They significantly reduced the imbalances, but not sufficient to completely suppress the imbalance fluctuations. The requirement of stability for the BPM system for the upgrade plan of SPring-8 is going to be more stringent. We started extensive survey to find the sources of fluctuations of the gain imbalances in order to achieve long-term stability of the BPM system applicable to the planned SPring-8 upgrade. S. Sasaki, T. Fujita et al., Proc. of the DIAPC 2007, Venice, Italy, (2007) p. 114 ** M. Masaki et al., Proc. of the 11th Symp. on Accel. Sci. and Technol., (1997), p.83.
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Paper

Title

Page

Long-Term Stability of the Beam Position Monitors at SPring-8

359

T. Fujita, H. Dewa, M. Masaki, S. Matsubara, S. Sasaki, S. Takano
JASRI/SPring-8, Hyogo-ken, Japan
H. Maesaka, Y. Otake
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan

At the SPring-8 storage ring, the renewal of BPM electronics in 2006 has improved orbit feedback resolution *. However, a stability issue of the whole BPM system, including the buttons, the cables and the electronics, remains to be settled for long-term stability of the beam orbit. The BPM in the present SPring-8 has gain imbalances among 4 electrode channels, which result in large offsets (~1 mm). The imbalances are routinely corrected in accordance with a beam-based measurement **. But, the offset error increases close to 100 um during the operation, because of the imbalance fluctuations. Major origin of the imbalances is standing waves caused by reflections in BPM cables. As a countermeasure for the imbalance issue, isolators to mitigate the standing waves were equipped. They significantly reduced the imbalances, but not sufficient to completely suppress the imbalance fluctuations. The requirement of stability for the BPM system for the upgrade plan of SPring-8 is going to be more stringent. We started extensive survey to find the sources of fluctuations of the gain imbalances in order to achieve long-term stability of the BPM system applicable to the planned SPring-8 upgrade.
* S. Sasaki, T. Fujita et al., Proc. of the DIAPC 2007, Venice, Italy, (2007) p. 114
** M. Masaki et al., Proc. of the 11th Symp. on Accel. Sci. and Technol., (1997), p.83.

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