Observation of coherent synchrotron radiation from the NSLS VUV ring

We report the observation of multiparticle coherent emission in the very fa r infrared from bunched electrons in an electron storage ring. The emission occurs in quasi-periodic bursts, and only when the electron beam current e xceeds a threshold value, suggesting an instability-driven modulation of th e electron bunch density. For the operating conditions reported, the spectr al content of the coherent emission is peaked near a wavelength of 7 mm. Th is wavelength is much shorter than the nominal electron bunch length, indic ating the presence of a density modulation within the bunch. (C) 2001 Publi shed by Elsevier Science B.V.