In order to reach the high peak current required for an x-ray FEL, two separate magnetic dipole chicanes are used in the LCLS accelerator to compress the electron bunch length in stages. In these bunch compressors, coherent synchrotron radiation (CSR) can be emitted-induced either by a short electron bunch, or by any longitudinal density modulation that may be on the bunch. We present measurements, simulations, and analysis of (1) the CSR-induced energy loss, (2) the related transverse emittance growth, and (3) the microbunching-induced CSR directly observed at optical wavelengths
