The Impedance of Flat Metallic Plates with Small Corrugations

This report summarizes recent work on using a device composed of two flat, metallic plates with small corrugations (sometimes called a dechirper) at the end of linac-based, X-ray free electron lasers (FELs) for energy chirp control and as a passive fast kicker. We present an analytical theory of the wakefields/impedances of such dechirpers, followed by comparisons with numerical simulations, and comparisons with measurements at the Linac Coherent Light Source (LCLS). We show that agreement in all cases was found to be excellent. The theoretical and simulation work presented includes work originally performed in collaboration with, in particular, G. Stupakov, I. Zagorodnov, and E. Gjonaj.