Abstract
In order to reach the high peak current required for an x-ray free electron laser, two separate magnetic dipole chicanes are used in the Linac Coherent Light Source accelerator to compress the electron bunch length in stages. In these bunch compressors, coherent synchrotron radiation (CSR) can be emitted either by a short electron bunch or by any longitudinal density modulation that may be on the bunch. In this paper, we report detailed measurements of the CSR-induced energy loss and transverse emittance growth in these compressors. Good agreement is found between the experimental results and multiparticle tracking studies. We also describe direct observations of CSR at optical wavelengths and compare with analytical models based on beam microbunching.
Highlights
Coherent synchrotron radiation (CSR) is one of the most challenging issues associated with the design of bunch compressor chicanes for advanced accelerators and x-ray facilities
We present detailed measurements of CSR-induced energy loss and transverse emittance growth at two bunch compressors for the Linac Coherent Light Source (LCLS), an x-ray free-electron laser currently in the final phase of the commissioning at SLAC
We report direct observations of CSR at optical wavelengths on one of the LCLS optical transition radiation (OTR) screens and compare with analytical models based on beam microbunching
Summary
Coherent synchrotron radiation (CSR) is one of the most challenging issues associated with the design of bunch compressor chicanes for advanced accelerators and x-ray facilities. Effects of CSR on electron beam quality have been studied extensively in theory and simulations CSR can be emitted for wavelengths longer than the electron bunch length and for shorter wavelengths if the electron beam has high-frequency density modulations caused by a microbunching instability [7,8]. It was found during the LCLS injector commissioning [9] that the presence of a microbunched beam contributes significantly to the enhancement of the optical signal on optical transition radiation (OTR) diagnostic screens after bends. We report direct observations of CSR at optical wavelengths on one of the LCLS OTR screens and compare with analytical models based on beam microbunching
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