TIME-RESOLVED ELECTRON SPECTRUM DIAGNOSTICS FOR A FREE-ELECTRON LASER

Time-resolved electron-beam diagnostics have been developed for use wi th free-electron lasers (FELs) and associated electron sources, based on the techniques of secondary electron emission and optical transitio n radiation (OTR). The 32-channel OTR detector forms part of a high-re solution (0.18%) electron spectrometer with a time resolution of 50 ns . Variable-magnification optics allow the spectrometer to view single- macropulse spectra with widths in the range of 0.2%-7%; wider spectra are taken with several momentum settings. Design criteria for the spec trometer are presented, and experience of operating with the diagnosti cs over a range of FEL physics experiments is summarized. The spectrom eter is used, in conjunction with optical diagnostics, in studies at F ELIX of efficiency enhancement, pulse chirping, and stepped-undulator operation. (C) 1996 American Institute of Physics.