Abstract
Simulations of the x-ray free-electron laser (FEL) oscillator are presented that include the frequency-dependent Bragg crystal reflectivity and the transverse diffraction and focusing using the two-dimensional FEL code GINGER. A review of the physics of Bragg crystal reflectors and the x-ray FEL oscillator is made, followed by a discussion of its numerical implementation in GINGER. The simulation results for a two-crystal cavity and realistic FEL parameters indicate $\ensuremath{\sim}{10}^{9}$ photons in a nearly Fourier-limited, ps pulse. Compressing the electron beam to 100 A and 100 fs results in comparable x-ray characteristics for relaxed beam emittance, energy spread, and/or undulator parameters, albeit in a larger radiation bandwidth. Finally, preliminary simulation results indicate that the four-crystal FEL cavity can be tuned in energy over a range of a few percent.
Highlights
With the success of the Linear Coherent Light Source (LCLS) [1], we are entering the era of x-ray free-electron lasers (FELs) that realize an enormous improvement in brightness and coherence over that possible with thirdgeneration synchrotron x-ray sources
An x-ray FEL oscillator [4] was proposed in the 5–20 keV energy range that can potentially offer complementary performance to sources based on spontaneous emission (SASE), with $103 lower peak powers, $103 narrower spectral bandwidth, and $103 higher repetition rate
In this paper we investigated the performance of the x-ray FEL oscillator using two-dimensional GINGER simulations
Summary
With the success of the Linear Coherent Light Source (LCLS) [1], we are entering the era of x-ray free-electron lasers (FELs) that realize an enormous improvement in brightness and coherence over that possible with thirdgeneration synchrotron x-ray sources. This paper begins to address the latter two areas, i.e., the physics of the x-ray FEL cavity, by incorporating Bragg diffraction of x rays from crystals into the well-known axisymmetric FEL code GINGER [6] In this manner, various FEL parameter and design studies can be done that model both the relevant electron beam physics (such as energy spread, emittance, and longitudinal current profile) and the radiation propagation (including reflection, filtering, and focusing by crystals and mirrors). Via a four-mirror geometry, preliminary simulations show that tens of MW of 14 keV x rays can be produced and varied over a photon energy range $6%
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