HOM-free linear accelerating structure for e/sup +/e/sup -/ linear collider at C-band

The HOM-free linear acceleration structure using the choke mode cavity (damped cavity) is now under design for the e/sup +/e/sup -/ linear collider project at C-band frequency (5712 MHz). Since this structure shows a powerful damping effect on most or all HOMs, there is no multibunch problem due to long range wakefields. The structure will be equipped with microwave absorbers in each cell and also the in-line dummy load in the last few cells. The straightness tolerance for a 1.8 m long structure is looser than 30 /spl mu/m for the 25% emittance dilution limit, which can be achieved by standard machining and braising techniques. Since it has good vacuum pumping conductance through annular gaps in each cell, instabilities due to the interaction of the beam with the residual-gas and ions can be minimized.