Recent Progress on Beam Stability Study in the Psr

A fast transverse instabilityhas been observed in the Los Alamos Proton Storage Ring (PSR) when the injected beam intensity reaches more than 2 10 protons per pulse. Understanding the cause and control of this instability has taken on new importance as the neutron-scattering community considers the next generation of accelerator-driven spallation-neutron sources, which call for peak proton intensities of 10 per pulse or higher. Previous observations and theoretical studies indicate that the instability in the PSR is most likely driven by electrons trapped within the proton beam. Recent studies using an experimental electronclearing system and voltage-biased pinger-electrodes for electron clearing and collection support this hypothesis. Experiments have also been performed to study the instability threshold when varying the electron production rate. Theoretical studies include a computer simulation of a simpli®ed model for the e p instability and the investigation of possible electron con®nement in the ring-element magnetic ®elds. This paper reports some recent results from these studies.