Flattop operation of the ILC accelerating cryomodule

Abstract

A 500 GeV center-of-mass International Linear Collider (ILC), currently under R&D development, is foreseen as the next-generation high-energy physics (HEP) instrument [1]. The achievement of a 31.5 MV/m average operational accelerating gradient in a single cryomodule is a proof of principle for the ILC project. However, individual cavity performance may have a large spread in operating gradients, up to 20% of the nominal value [2, 3]. In case of cavities performing below the average, the design parameters could be achieved by tweaking the RF distribution accordingly. We present a simple theoretical analysis of the ILC cryomodule operation with a gradient spread. The difference in the gradients breaks the synchronism of a transient processes in each cavity and causes nonuniform acceleration along the bunch train. A proper solution was found to maintain flattop operation of the accelerating module. Finally, we perform numerical efficiency estimations for the proposed RF distribution scheme based on real data of the gradient spread of actual cavities.