Abstract
Coherent synchrotron radiation (CSR) is of great interest to those designing accelerators as drivers for free-electron lasers (FELs). Although experimental evidence is incomplete, CSR is predicted to have potentially severe effects on the emittance of high-brightness electron beams. The performance of an FEL depends critically on the emittance, current, and energy spread of the beam. Attempts to increase the current through magnetic bunch compression can lead to increased emittance and energy spread due to CSR in the dipoles of such a compressor. The code elegant was used for design and simulation of the bunch compressor [M. Borland et al., in Proceedings of the 2000 Linear Accelerator Conference, Monterey, CA (SLAC, Menlo Park, CA, 2001), p. 863] for the low-energy undulator test line (LEUTL) FEL [S. V. Milton et al., Phys. Rev. Let. 85, 988 (1999)] at the Advanced Photon Source (APS). In order to facilitate this design, a fast algorithm was developed based on the 1D formalism of Saldin and co-workers [E. L. Saldin, E. A. Schneidmiller, and M. V. Yurkov, Nucl. Instrum. Methods Phys. Res., Sect. A 398, 373 (1997)]. In addition, a method of including CSR effects in drift spaces following the chicane magnets was developed and implemented. The algorithm is fast enough to permit running hundreds of tolerance simulations including CSR for 50 000 particles. This article describes the details of the implementation and shows results for the APS bunch compressor.
Highlights
It has long been known that electrons traveling through a bending magnet emit radiation
Recently has it become widely accepted that, when very short electron bunches travel through a dipole magnet, they can emit coherently at wavelengths that are comparable to the bunch length and can propagate in the vacuum chamber
We describe in simple terms why coherent synchrotron radiation (CSR) has an impact on the electron beam
Summary
It has long been known that electrons traveling through a bending magnet emit radiation. This, together with the fact that the emission is coherent and at a wavelength comparable to the bunch length, results in a modulation of the energy along the bunch This is similar to a wakefield but, unlike wakefields, CSR affects the particles ahead of the emitting particles rather than behind. (For convenience, in this paper the phrase “CSR wake” is used in spite of this difference.) Since this is happening inside a dipole magnet, the energy modulation results in a modulation of the transverse slopes in the bending plane, which increases the projected transverse emittance in the bending plane. An effort similar to the present work but using a simplified formulation and an assumption of Gaussian longitudinal distributions was reported for PARMELA by Dowell and O’Shea [6] This latter work did not attempt to include CSR in the drift spaces following dipoles
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