Review of ultra high-gradient acceleration schemes, results of experiments

A dramatic improvement in energy gain per unit cost is mandatory for the future of very high energy accelerators, for which RF- acceleration would be replaced by new techniques. Several schemes have been proposed (laser driven, beam driven accelerators) and tested. A critical review of these schemes and experimental results is presented, with considerations on the most promising techniques and the effort still needed. Important parameters for high luminosity (efficiency, emittance preservation,...) are discussed. (36 refs).