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 ∼ 1.8μs 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.