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 KEKB rings are presented. (author)