The electron-cloud instability in PEP-II: an update

We present an update on the estimate of the growth time of the multi-bunch transverse instability in the PEP-II collider arising from the interaction of the positron beam with the accumulated electron cloud. We estimate the contributions to the growth rate arising from the dipole magnets and from the pumping straight sections. We emphasize those quantities upon which the instability is most sensitive. The simulation includes measured data on the secondary emission yield for TiN-coated samples of the actual vacuum chamber. Although our analysis is still in progress, we conclude that the instability risetime is of order 1 ms, which is well within the range controllable by the feedback system.