Development of a high-speed digital signal process system for bunch-by-bunch feedback systems

High-speed digital filter systems for bunch-by-bunch feedback systems have been developed at KEK. A two-tap finite impulse response filter with simple hardware realizes the functions of a 90° phase shift, suppression of the static component and digital delay of up to a few hundred turns for the KEKB rings. Difficulties in the circuit board, such as the trimming of the timing skews or the problem of long-term reliability, have been solved using custom GaAs large-scale integrated circuits which demultiplex and multiplex fast parallel-digital data coming from the analog-to-digital converter and going to the digital-to-analog converter. Two major applications of the filter board, the bunch current monitor and the bunch oscillation recorder with 20 MB memories for transient-domain analysis of the instabilities, are also described

Feedback experiments in TRISTAN-AR and the bunch by bunch feedback systems for KEKB

. Beam tests of the KEKB bunch by bunch feedback system prototypes have been performed in the TRISTAN-AR in both longitudinal and transverse planes. A two-tap FIR filter system, consisting of hardware logic's, realized the function of the phase shift by 90 degrees, the suppression of the static component and the delay of up to a few tens of turns in longitudinal plane with 508 MHz of system clock. The transverse systems were purely analog systems without any digital signal processing part. More than 100 bunches with maximum current of 376 mA have been accumulated successfully with the bunch spacing of 2 ns. The growth time and the growing modes of the transverse instabilities has also been measured with the memory function of the two-tap FIR filter. It suggests that the bunch-by-bunch feedback system is a powerful tool to explore the source of the instabilities. Based on the results of the AR experiments, the design and the expected performances of the feedback systems for KE..

設立後のKEKでの共同利用形態の変遷

第２章　基盤機関の成立史菊谷　英司 [KEK]（高エネルギー加速器科学研究科

原子核研究所とその共同利用に関する報告

第Ⅰ部　研究会「大学共同利用研究所・研究機関の成立」 第3章菊谷 英司［高エネルギー加速器研究機構、加速器研究施設

Observation Of Transverse Coupled Bunch Instability At

Transverse coupled bunch instability was experimentally studied in low energy positron ring (LER) and high energy electron ring (HER) at KEKB. The oscillations of bunches were recorded by a bunch oscillation recorder for the total of 4096 turns. The data were analysed to obtain the mode distribution and the growth rate of oscillation. The result of the analysis is presented in this paper