Recently during the commissioning of the 10kW FEL at Jefferson Lab, a sudden increase of the bunch energy spread is observed when the bunch is tuned from under compression to over compression in the bunch compression chicane right in front of the wiggler. In this talk, we present our preliminary analytical result of the effective longitudinal force due to coherent synchrotron radiation (CSR), which also shows a sudden increase in its magnitude at the cross-over of full compression point. This analysis takes account of the effect of bunch tilting on the retardation relation as a result of the energy-chirping induced longitudinal-horizontal correlation of the bunch distribution in dispersive regions.


Talk Slides: (slides )