Emittance Control In Linear Colliders

In this paper, we discuss the generation and control of the emittance in a next-generation linear collider. The 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 pre-acceleration 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. The proposed vertical beam sizes at the interaction point are the order of a few nanometers while the horizontal sizes are about a factor of 100 larger. This cross-sectional area is about a factor of 104 smaller than the SLC. However, the main question is: what are the tolerances to achieve such a small size, and how do they compare to present techniques for alignment and stability These tolerances are very design dependent. Alignment tolerances in the linac can vary from 1 [mu]m to 100 [mu]m depending upon the basic approach. In this paper we discuss techniques of emittance generation and control which move alignment tolerances to the 100 [mu]m range.