G. V. Stupakov (SLAC)
Interaction between the bunches in the NLC main linac via long range wakefields can cause a beam breakup instability similar to the beam breakup of a single bunch. Although the magnitude of the long range wakefields for an ideal NLC structure is below the instability threshold, the wake is sensitive to the manufacturing errors. In case of large errors, the developing instability can result in the projected emittance dilution of the bunch train, and imposes tight tolerances on structure misalignments and the beam jitter. To suppress the instability, we propose to introduce an energy spread between the bunches, similar to the BNS energy spread for damping of the beam breakup within a single bunch [1]. Based on simple estimates, we show that the energy spread of order of 1-2% should be enough for suppression of the instability. We also present the results of computer simulations with the simulation code LIAR for the NLC nominal beam parameters for two different energy profiles within the train. The simulations confirm our theoretical estimate and indicate that both the tolerances for structure misalignments and the incoming beam jitter can be considerably loosened by introducing the energy spread within the beam.
[1] V. Balakin, A. Novokhatsky, and V. Smirnov, in Proceedings of the 12th International Conference on High Energy Accelerators, Fermilab, 1984, p119.
*Work supported by DOE contract DE-AC03-76SF00515.
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