Emittance dilution due to slow alignment drifts in the main linacs of the NLC

The tight tolerances in the main linacs of the Nest Linear Collider (NLC) result in a large sensitivity of the beam emittance to slow alignment drifts. Once the accelerator is tuned, the optimized emittances must be maintained. Slow alignments drifts will make resteering and reoptimization necessary. The frequency of these linac reoptimizations is an important parameter that determines how well the linear collider can be operated. We present simulation results that address this question for the main linacs of the NLC. We will show that the effects of alignment drifts can indeed be handled.