DIPOLE MODE DETUNING IN THE INJECTOR LINACS OF THE NLC.

The injector linacs of the JLC/NLC project include the prelinac, the e{sup +} drive linac, the e{sup -} booster, and the e{sup +} booster. The first three will be S-band machines, the last one, an L-band machine. We have demonstrated that by using detuning alone in the accelerator structure design of these linacs we will have acceptable tolerances for emittance growth due to both injection jitter and structure misalignments, for both the nominal (2.8 ns) and alternate (1.4 ns) bunch spacings. For the L-band structure (a structure with 2{pi}/3 phase advance) we take a uniform distribution in synchronous dipole mode frequencies, with central frequency {bar f} = 2.05 GHz and width {Delta}{sub {delta}f} = 3%. For the S-band case our optimized structure (a 3{pi}/4 structure) has a trapezoidal dipole frequency distribution with f = 3.92 GHz, {Delta}{sub {delta}f} = 5.8%, and tilt parameter {alpha} = -.2. The central frequency and phase advance were chosen to put bunches early in the train on the zero crossing of the wake and, at the same time, keep the gradient optimized. We have shown that for random manufacturing errors with rms 5 {micro}m, (equivalent to 10{sup -4} error in synchronous frequency), the injection jittermore » tolerances are still acceptable. We have also shown that the structure alignment tolerances are loose, and that the cell-to-cell misalignment tolerance is {approx}> 40 {micro}m. Note that in this report we have considered only the effects of modes in the first dipole passband.« less