The electron cloud instability at PEP-II

The electron cloud instability (ECI) at PEP-II enlarges the positron beam size at high currents and reduces the luminosity. The electrons for this instability come from multipacting electrons in the straight section vacuum chambers and, perhaps, photo-emission and secondary emission of electrons from the vacuum ante-chambers in the arcs. Solenoid and transverse field magnets have been placed over the vacuum chambers with about a 30 gauss field to suppress ECI. These fields have been successful in reducing the positron beam size blow up. Only about half of the drift vacuum chambers in LER have been wound with solenoids. Earlier ECI measurements were described previously.