SPONTANEOUS COHERENT MICROWAVE EMISSION AT SURF III.

Following the long established theory of synchrotron radiation emission, all synchrotron radiation is emitted in harmonics of the frequency of the accelerating radio-frequency field. Researchers at NIST have made this "picket-fence" structure visible at the Synchrotron Ultraviolet Radiation Facility, SURF III, for microwave radiation emitted at frequencies around 10 GHz, which corresponds to the 100th harmonic. This microwave radiation was easily detectable, because of its coherent enhancement by a "sawtooth" or longitudinal bunch instability in the electron beam. A collaborative study of this phenomenon with researchers at the Argonne National Laboratory's Advanced Photon Source is reported in the May 2001 issue of the journal Physical Review Special Topics--Accelerators and Beams.

The major breakthrough in this study was the identification of the connection between spontaneous coherent synchrotron radiation emission, micro-bunching, intensity noise in the visible spectral range, and the sawtooth instability, which has long been known to affect SURF under certain operating conditions. This greater understanding of SURF III beam dynamics has contributed significant improvements in beam stability that have been obtained recently.