Future e+ e- linear colliders and beam-beam effects

As designers of the high energy accelerators of the future, the first question asked is, What do the particle physicists want? It is a fundamental fact of nature that the cross sections for the production of interesting events in electron-positron collisions in the TeV energy range tend to fall-off inversely as the square of the particle energy. The luminosity for two colliding beams, either in a storage ring or from a linear collider, is defined as the event rate divided by the cross section. In order to keep the event rate at an acceptable level, the luminosity must, therefore, increase approximately as the square of the beam energy. The luminosities which follow this scaling are shown for four collider energies. The choice of linac parameters is strongly coupled to various beam-beam effects which take place when the electron and positron bunches collide. These beam-beam effects are summarized and the RF design of a 650 GeV center-of mass collider is discussed