Wakefields in the LCLS

For a short bunch in an elliptical collimator we demonstrate that, as in a purely round collimator, the wake can be estimated from the primary fields of the beam alone. We obtain the wakes in the LCLS rectangular-to-round, undulator transitions using a hybrid method that includes indirect numerical (field) integration and an analytical potential energy term. For the LCLS 1 nC bunch charge configuration, we find the wake-induced energy change in the transitions to be small compared to that due to the resistance of the beam pipe walls. Abstract For a short bunch in an elliptical collimator we demonstrate that, as in a purely round collimator, the wake can be estimated from the primary fields of the beam alone. We obtain the wakes in the LCLS rectangular-to-round, undu-lator transitions using a hybrid method that includes indirect numerical (field) integration and an analytical potential energy term. For the LCLS 1 nC bunch charge configuration , we find the wake-induced energy change in the transitions to be small compared to that due to the resistance of the beam pipe walls.