Observation of coherent microwave transition radiation in the APS linac

The APS injector includes a conventional S-band linear accelerator with three separate electron sources. Two electron guns are used as primary and secondary sources for injection into the APS 7-GeV storage ring, while a separate laser photocathode gun is available for free-electron laser (FEL) research. We report here the results of the dependence of 30-GHz coherent microwave transition radiation on electron bunch length. Sensitivity to pulses as short as 200 to 300 femtoseconds has been demonstrated.