Abstract
A microbunching instability driven by longitudinal space charge, coherent synchrotron radiation, and linac wakefields is studied for the linac coherent light source (LCLS) accelerator system. Since the uncorrelated (local) energy spread of electron beams generated from a photocathode rf gun is very small, the microbunching gain may be large enough to significantly amplify rf-gun generated modulations or even shot-noise fluctuations of the electron beam. The uncorrelated energy spread can be increased by an order of magnitude to provide strong Landau damping against the instability without degrading the free-electron laser performance. We study different damping options in the LCLS and discuss an effective laser heater to minimize the impact of the instability on the quality of the electron beam.
Highlights
An x-ray free electron laser (FEL) is the primary candidate for a fourth-generation light source that provides extremely bright x-ray photons with femtosecond time resolution [1,2]
Instability, the pulse length of a low-emittance electron bunch generated from the photocathode rf gun is magnetically compressed in the linear accelerator by more than 1 order of magnitude
Numerical and theoretical investigations of high-brightness electron bunch compression reveal a microbunching instability driven by coherent synchrotron radiation (CSR) that can significantly degrade the beam quality [3,4,5,6]
Summary
An x-ray free electron laser (FEL) is the primary candidate for a fourth-generation light source that provides extremely bright x-ray photons with femtosecond time resolution [1,2]. Numerical and theoretical investigations of high-brightness electron bunch compression reveal a microbunching instability driven by coherent synchrotron radiation (CSR) that can significantly degrade the beam quality [3,4,5,6]. Significant LSC-induced energy modulation in the deep ultraviolet FEL (DUVFEL) linac has been experimentally characterized using an rf zero-phasing method [8]. The electron energy profile generated from a laser heater with a laser spot size large compared to the transverse size of the electron beam deviates significantly from a Gaussian distribution and is not effective in smearing the short-wavelength microbunching. With a laser spot size matched to the transverse size of the electron beam, the laser heater generates a nearly Gaussian energy distribution and can be used to minimize the instability effects.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
