Emittance control in linear colliders

The author discusses the generation and control of the emittance in a next-generation linear collider. Beams are extracted from a damping ring and compressed in length by the first bunch compressor. They are then accelerated in a preaccelerator linac up to an energy appropriate for injection into a high gradient linac. In many designs this preacceleration is followed by another bunch compression to reach a short bunch. After acceleration in the linac, the bunches are finally focused transversely to a small spot. Techniques of emittance generation and control which move alignment tolerances to the 100- mu m range are discussed.<>