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Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357
Strong enhancements of the optical transition radiation (OTR) signal sampled after bunch compression in the Advanced Photon Source (APS) linac chicane have been observed as has been reported in LCLS injector commissioning. A FIR CTR detector and interferometer were used to monitor the bunch compression process of the PC gun beam down to sub-0.5 ps (FWHM) and correlate the appearance of spatially localized spikes of OTR signal (5 to 10 times brighter than adjacent areas) within the beam image footprint. We also observed that a beam from a thermionic cathode gun with much lower charge per micropulse (but a similar total macropulse charge to the PC gun) showed no enhancement of the OTR signal after compression. Reconstructions of the temporal profiles from the autocorrelations of both beams were performed and will be presented. Spectral-dependence measurements of the enhanced OTR were done initially at the 375-MeV station using a series of bandpass filters inserted before the CCD camera. Tests with an Oriel spectrometer with ICCD readout are now being planned to extend those studies. Discussions of the possible mechanisms for the OTR enhancements will be presented.
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Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
An energy recovery linac based light source is a potential revolutionary upgrade to the Advanced Photon Source (APS) at Argonne National Laboratory. The concept relies on several key research areas, one of which is the generation of ultra-low emittance, high-average-current electron beams. In this paper, we present our investigation of a dc-gun-based system for ultra-low emittance bunches in the 20 pC range. A parallel multi-objective numerical optimization is performed in multi-parameter space. Parameters varied include experimentally feasible drive-laser shapes, the dc gun voltage, and the thermal energy of the emitted photo-electrons. Our goal is to deliver a 10 MeV, 20 pC bunch at the entrance of the linac with an emittance of 0.1 μm or lower, rms bunch length of 2 to 3 ps, and energy spread no larger than 140 keV. We present the machine parameters needed to generate such an injector beam, albeit without a merger.
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