  Magnetic compressors offer an attractive path toward jitter-free bunch
compression in MeV-UED. Compared with RF bunchers, magnetic compressors do not
introduce additional timing jitter and can be configured to minimize timing
jitter due to upstream energy fluctuation. In this work we discuss the
principles of designing magnetic compressors for MeV-UED. Start-to-end
simulation of a dogleg compressor is presented. Results show a bunch length of
11~fs can be achieved at 100 fC charge with small emittance growth.
