Characterization and mitigation of coherent-optical-transition-radiation signals from a compressed electron beam

The Advanced Photon Source (APS) injector complex includes an option for rf photocathode (PC) gun beam injection into the 450-MeV S-band linac. At the 150-MeV point, a four-dipole chicane was used to compress the micropulse bunch length from a few ps to sub-0.5 ps (FWHM). Noticeable enhancements of...

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Bibliographic Details
Published in:Physical review special topics. PRST-AB. Accelerators and beams 2009-08, Vol.12 (8), p.080702, Article 080702
Main Authors: Lumpkin, A. H., Sereno, N. S., Berg, W. J., Borland, M., Li, Y., Pasky, S. J.
Format: Article
Language:English
Subjects:
Bandpass filters
Beam injection
Broadband
Chicanes
Coherent light
Dipoles
Electron beams
Far infrared radiation
Imaging spectrometers
Injectors
Light sources
Optical communication
Optical transition
Photocathodes
Photon beams
Radiation
Radiation detectors
Signal processing
Spikes
Visible spectrum
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Summary:The Advanced Photon Source (APS) injector complex includes an option for rf photocathode (PC) gun beam injection into the 450-MeV S-band linac. At the 150-MeV point, a four-dipole chicane was used to compress the micropulse bunch length from a few ps to sub-0.5 ps (FWHM). Noticeable enhancements of the optical transition radiation (OTR) signal sampled after the APS chicane were then observed as has been reported in the Linac Coherent Light Source (LCLS) injector commissioning. A far-infrared (FIR) coherent transition radiation detector and interferometer were used to monitor the bunch compression process and correlate the appearance of localized spikes of OTR signal (5 to 10 times brighter than adjacent areas) within the beam-image footprint. We have performed spectral-dependency measurements at 375 MeV with a series of bandpass filters centered in 50-nm increments from 400 to 700 nm and with an imaging spectrometer and observed a broadband enhancement in these spikes. Mitigation concepts of the observed coherent OTR, which exhibits an intensity enhancement in the red part of the visible spectrum as compared to incoherent OTR, are described.
ISSN:1098-4402
1098-4402
2469-9888
DOI:10.1103/PhysRevSTAB.12.080702