Conference

Accelerating Structures for Multibunches

M. Dohlus

DESY, Hamburg, Germany

Abstract

Although the interaction between beam and fundamental mode is by far the strongest multibunch effect (beam loading), this process can be handled well by choosing an appropriate mode of operation (eg. staggered timing or shaped klystron pulses). In contrast to this, the higher order mode effects depend strongly on mechanical tolerances and need a special structure design to prevent multibunch beam break-up or emittance dilution: Cell-to-cell and structure-to-structure detuning are based on small variations of the cell geometry to decohere the HOM wakefield contributions. Effective HOM damping in long travelling-wave structures with either one or a few dampers is limited by the existence of trapped modes and the low velocity of the energy propagation. Even the reduced requirements of damping together with detuning can be fulfilled only with a large number of damper cells. Therefore different concepts of every-cell-dampers with strong impact to the structure design are proposed. A further improvement is expected by an active structure alignment that minimizes the HOM power in the damper loads.

sln 4 March 1996