Challenges on the high luminosity frontier of e+ e factories

For phi factories, tau-charm factories, and B factories to meet their respective luminosity goals, the circulating currents that typify e⁺ e^$colliders must be raised an order of magnitude. At the same time the beam size at the interaction point must be decreased. The approaches to realizing these conditions include increasing the charge per bunch, increasing the number of bunches in the collider, increasing the crossing angle for rapid bunch separation, tilting the bunch with respect to the direction of motion at the interaction point (“crab-crossing”), and minimizing the β function at the interaction point. The technological challenges implied by such strategies include the development of 1) novel rf-cavity designs to suppress higher order modes and to provide large rf-voltages for longitudinal focusing, 2) a new generation of powerful feedback electronics to control multi-bunch instabilities, and 3) vacuum chambers and pumping schemes suitable for operation with very high levels of synchrotron radiation. In high current colliders the design of the interaction region poses special problems of allowing rapid beam separation and avoiding excessive scattering of background radiation into the detector