Abstract
In this study, we investigate a new simple scheme using a planar undulator (PU) together with a properly dispersed electron beam ($e$ beam) with a large energy spread (${\sim}1\%$) to enhance the free-electron laser (FEL) gain. For a dispersed $e$ beam in a PU, the resonant condition is satisfied for the center electrons, while the frequency detuning increases for the off-center electrons, inhibiting the growth of the radiation. The PU can act as a filter for selecting the electrons near the beam center to achieve the radiation. Although only the center electrons contribute, the radiation can be enhanced significantly owing to the high-peak current of the beam. Theoretical analysis and simulation results indicate that this method can be used for the improvement of the radiation performance, which has great significance for short-wavelength FEL applications.
Highlights
Free-electron lasers (FELs), which serve as tunable coherent sources of short-wavelength radiation, have attracted considerable attention owing to their widespread application in spectroscopy[1], materials science[2], biology[3] and other fields[4, 5]
We investigate a simple scheme to improve the performance of the radiation using a planar undulator (PU) together with a properly dispersed e beam from the laser wakefield accelerators (LWFAs)
The growth rate remains constant at any horizontal position in the transverse gradient undulator (TGU) scheme and decreases when the electron deviates from the beam center in the PU scheme
Summary
Free-electron lasers (FELs), which serve as tunable coherent sources of short-wavelength radiation, have attracted considerable attention owing to their widespread application in spectroscopy[1], materials science[2], biology[3] and other fields[4, 5]. Remarkable progress has been made in generating high-energy (∼1 GeV), high-peak current (∼10 kA), and low-emittance (∼0.1 μm) electron beams (e beams) using laser wakefield accelerators (LWFAs) [10,11,12,13,14,15,16,17,18]. Such accelerators can be used for driving next-generation advanced light sources. Researchers have focused on compensating the large energy-spread effects in high-gain FELs by using a transverse gradient undulator (TGU) together with a properly dispersed e beam[23,24,25]. Theoretical analysis and numerical simulations demonstrate the feasibility of a self-amplified spontaneous emission (SASE) FEL with sub-gigawatt power, a narrow bandwidth (
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