Collective Effects Associated with Ultra-High Beam Intensities in Factories

The beam currents at the new e{sup +}e{sub {minus}} factories exceed those of conventional colliders by more than an order of magnitude. To achieve high luminosities the multi-bunch, high-current beams must be both longitudinally and transversely stable. Commissioning of the e{sup +}e{sub {minus}} factories has provided a wealth of new experimental data on beam stability in the regime of extremely high beam intensities. Many high-current effects have been studied including ion and dust trapping, issues relating to heavy beam loading, and positron beam emittance dilutions due to electron cloud instabilities arising from photoelectrons and/or multipacting inside the vacuum chamber. This paper will review the new experimental data on high intensity issues with emphasis on new effects.