Optimisation of the new low surface field accelerating structure for the ILC

The main superconducting radio frequency (SRF) linacs of the international linear collider (ILC) operate at a frequency of 1.3 GHz with a π phase advance per cell in the standing wave mode. An option being considered to reduce the overall footprint and project cost is to enhance the cavity gradient. The present baseline design for the main linacs of ILC demands the cavities to be able to reach a gradient of 35 MV/m—although during commissioning and operation the gradient will be 31.5 MV/m. This research concerns itself with the new cavity design with a view to reaching higher gradients. This design is focussed on minimising the surface electromagnetic fields and maximising the bandwidth of the accelerating mode. This new shape, which is referred to as the New Low Surface Field (NLSF) design. A design of a complete nine-cell cavity, including power couplers and higher order mode damping couplers is presented.