| Paper | Title | Page |
|---|---|---|
| TUPC47 | Observations on COTR Due to the Microbunching Instability in Compressed Beams | 352 |
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The observations of the strong enhancements of the optical transition radiation (OTR) signal observed after bunch compression of photocathode beams in the Advanced Photon Source (APS) linac chicane and at the Linac Coherent Light Source (LCLS) continue to be of interest. Spectral-dependence measurements of the coherent OTR (COTR) were done at APS initially at the 375-MeV station using a series of band pass filters inserted before the CCD camera, but recent tests with an Oriel spectrometer with ICCD readout have extended those studies. In this case we used a microchannel plate image intensifier with a GaAs photocathode to explore the NIR regime out to 880 nm. We report for the first time an ~40% intensity modulation of ~20-nm period throughout the observed broadband COTR spectra for some localized spatial structures. This effect was observed at full electron beam compression as determined from the CTR monitor located after the chicane, and it persisted with two different grating dispersions and for different spectrometer offsets. In addition, the observation of a ring-like COTR image structure in x-y space for a mismatched beam at 355 MeV will be presented and discussed. |