Flattop operation of the ILC accelerating cryomodule

A 500 GeV center-of-mass International Linear Collider (ILC), currently under R and D development, is foreseen as next-generation high-energy physics instrument. Achieving of 31.5 MV/m average operational accelerating gradient in a single cryomodule is a proof-of-principle for ILC project. However, the individual cavity performance may have a large spread in operating gradients, up to 20% of the nominal value. In case of cavities performing below the average, the designed parameters could be achieved by tweaking the RF distribution accordingly. We present the simple theoretical analysis of ILC cryomodule operation with a gradient spread. The difference in the gradients breaks the synchronism of transient processes in each cavity and causes nonuniform acceleration along the bunch train. The proper solution was found to keep the accelerating module flattop operation. Finally we do the numerical efficiency estimations for the proposed RF distribution scheme based on real data of actual cavities gradient spread