Abstract
We present a numerical study that characterizes the dependence on the radiator length of the output power produced by a free-electron laser (FEL) operated in the high gain harmonic generation (HGHG) configuration. Using the main parameters of the FERMI@Elettra FEL, numerical simulations of the FEL process have been performed for different lengths of the radiator. Our results show that in the case of HGHG the achievable output power has a dependence on the radiator length that is linear. The impact of the electron beam parameters on the achievable maximum power vs radiator length dependence is also studied. A normalization of the results to the FEL saturation power and to the FEL gain length shows that this dependence can be expressed by a universal linear equation that, in some conditions, is independent on the electron beam current and brightness. The reported results could be useful for the design of future FELs based on the HGHG scheme and could be used for a quick estimate of the best undulator length.
Highlights
Free-electron lasers (FELs) based on high brightness electron beams are becoming a key instrument in the recent development of science
Experiments have been done in different experimental conditions, including very different electron beam and undulator parameters, all experiments have shown the capability of high gain harmonic generation (HGHG) to produce FEL pulses with a wellcontrolled and narrow bandwidth
In order to study the effects of radiator length, we performed series of numerical simulations of the FEL process
Summary
Free-electron lasers (FELs) based on high brightness electron beams are becoming a key instrument in the recent development of science. Between possible schemes that can be used to produce FEL pulses in the VUV–soft x ray there is particular interest on high gain harmonic generation (HGHG) [6] that uses an external laser to initiate the process and can improve the FEL coherence and stability. The use of harmonic generation to produce FEL pulses at short wavelength starting from an external seed laser at long wavelength was originally proposed in [7] and was applied to high gain single pass FELs to generate IR [8] and VUV coherent emission [9]. The undulator does not apply, especially in cases where the undulator length is less than a meter In those cases, the FEL power only has coherent emission in the radiator without exponential gain and the process is generally called coherent harmonic generation (CHG).
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