Gabriel Marcus

Self-seeded FEL wavelength extension with high-gain harmonic generation

We study a self-seeded high-gain harmonic generation (HGHG) free-electron laser (FEL) scheme to extend the wavelength of a soft X-ray FEL. This scheme uses a regular self-seeding monochromator to generate a seed laser at the wavelength of 1.52 nm, followed by a HGHG configuration to produce coherent, narrow-bandwidth harmonic radiations at the GW level. The 2nd and 3rd harmonic radiation are investigated with start-to-end simulations. Detailed studies on the FEL performance and shot-to-shot fluctuations are presented.

Application of x-ray simulations in development of instruments at Linear Coherent Light Source (LCLS) at National Accelerator Laboratory (SLAC) (Conference Presentation)

Development of X-ray Free Electron Lasers (XFEL) opens new era in X-ray science. The full exploitation of unique properties of the XFEL radiation require challenging solutions that preserves radiation properties from a coherent, diffraction limited source under unprecedented instantaneous and average power load. We will present properties of simulated XFEL radiation such as coherence, source shape, divergence and longitudinal location inside the undulator. Recently, a construction of the LCLS II project has started as a major upgrade to the LCLS facility that will increase the average power of the XFEL up to 1 kW level. We will show how the X-ray simulations are used for minimizing thermal distortions on focusing of the LCLS II X-ray beams by 1 meter long Kirkpatrick-Baez mirrors. We will discuss and compare accuracy of simulations using different simulation methods and packages applied to focusing optics. The design of instruments should mitigate the damage to the optics caused by the tremendous instantaneous XFEL power. We will present X-ray simulation of the damage to the diffraction grating coatings and compare it with experimental results obtained at LCLS. The self-seeded mode of the LCLS operation increases temporal coherence and reduces greatly the bandwidth of the X-ray radiation. The results of time dependent X-ray simulations of the LCLS radiation passing through the seeding monochromator will be presented. We will compare two different approaches: Fourier Optics and an approach based on a dispersive system described by 6x6 pulse ray matrixes.

Design Optimization of Compensation Chicanes in the LCLS-II Transport Lines

LCLS-II is a 4th-generation high-repetition rate Free Electron Laser (FEL) based x-ray light source to be built at the SLAC National Accelerator Laboratory. To mitigate the microbunching instability, the transport lines from the exit of the linac to the undulators will include a number of weak compensation chicanes with the purpose of cancelling the momentum compaction generated by the main bend magnets of the transport lines. In this paper, we will report on our design optimization study of these compensation chicanes in the presence of both longitudinal and transverse space-charge effects.