Parameter optimization for the low frequency linacs in the NLC

In the present Next Linear Collider (NLC) design, S and L-band linacs are used to accelerate the beams to 10 GeV, where they are injected into the main X-band linacs. As injectors for the main accelerator, these linacs are required to deliver clean beams while being reliable and cost effective. These requirements set stringent tolerances on the design of the accelerators. There are two types of misalignment tolerances that are of great concern: cell-to-cell and structure-to-structure tolerances, which are dominated by long- and short-range wakefield effects, respectively. For a given lattice design, the structure-to-structure tolerance (which has strong impacts on girder configurations) is mainly determined by the global parameters such as the average iris size, the length and the type of the structure. This paper will discuss the optimization of the structure parameters to allow looser structure-to-structure tolerances; the cell-to-cell tolerance is related to the details of the single structure design and will not be addressed here. The optimization described here was based on a cost model for NLC and a wakefield scaling law for the tolerance estimations.