Bunching for shorter damping rings for the ILC

A variant rearrangement of the bunch trains for the ILC that enables much shorter damping rings is presented. In a particular example the ∼2820 bunches are regrouped into ∼550 subtrains of five adjacent bunches. These subtrains are extracted from the damping rings at ∼1.8 (micro)s intervals, obtaining the 1ms macrobunch length of the baseline TESLA collider scenario. If the baseline damping rf frequency is 325 MHz and the kicker rise and fall times are ∼20 ns, a ring circumference of ∼5.8km is required. Variations of the scheme could easily reduce the circumference to ∼4km, and faster kickers could reduce it even further