A Rapid Re-Design Method for the NLC DDS and Phase Stability of the Accelerating Mode: Implementation and Results

In order to reduce the dipole wake encountered by the first few bunches accelerated in a multibunch NLC scenario the DDS (damped detuned structure) was re-designed such that a much improved Gaussian fall-off occurs in the initial wake-function. From the 9 parameterised model of DDS 1 we use a mapping function to allow DDS 3 & 4 to be modeled and hence avoid additional and prohibitively time consuming MAFIA runs. The equivalent circuit parameters and geometrical parameters are treated as functions of the synchronous frequency and are readily mapped onto the new synchronous frequencies. The new geometrical parameters form a family where each is associated with the iris diameter. In order to assess the deviation of the phase from 2n/3 the difference between the new and old parameters is investigated. In many cases the difference is found to be of the order of a few tens of nanometers