Vertical Instability in KEK Booster

In the KEK Booster Synchrotron, from one msec after injection to extraction timing, beam intensity is stable, though it is reduced to about one half during one msec after injection. An instability of the vertical direction is one of the candidates of the beam loss. The e-folding time of the instability is less than 0.1 msec, and it strongly depends on the beam intensity and the horizontal beam position. We found that: (a) the instability occurred at 30 MHz and its bandwidth (FWHM) was 15 MHz, (b) the broad band coupling impedance resulted from several narrow band resonators, (c) these resonators were ferrite core bump magnets and kicker magnets.