Abstract
Together with one of its variants, the recently proposed phase-merging enhanced harmonic generation (PEHG) free-electron laser (FEL) is systematically studied in this paper. Different from a standard high-gain harmonic generation scheme, a transverse gradient undulator is employed to introduce a phase-merging effect into the transversely dispersed electron beam in PEHG. The analytical theory of the phase-merging effect and the physical mechanism behind the phenomenon are presented. Using a representative set of beam parameters, intensive start-to-end simulations for soft x-ray FEL generation are given to illustrate the performance of PEHG. Moreover, some practical issues that may affect the performance of PEHG are also discussed.
Highlights
The recent success of self-amplified spontaneous emission (SASE) based x-ray free-electron laser (FEL) facilities [1, 2] is enabling forefront science in various areas
In the high-gain harmonic generation (HGHG) scheme [9], typically a seed laser pulse is first used to interact with electrons in a short undulator, called modulator, to generate a sinusoidal energy modulation in the electron beam at the seed laser wavelength
In order to clearly and unanimously illustrates the physics behind it, we rename such a scheme as phase-merging enhanced harmonic generation (PEHG), further studies demonstrate that, this novel technique can be utilized for a real electron beam energy spread cooling in X-ray FEL linear accelerators [17]
Summary
The recent success of self-amplified spontaneous emission (SASE) based x-ray free-electron laser (FEL) facilities [1, 2] is enabling forefront science in various areas. A novel phase space manipulation technique, originally named as cooled-HGHG, has been proposed for significantly improving the frequency up-conversion efficiency of harmonic generation FELs [16]. In order to clearly and unanimously illustrates the physics behind it, we rename such a scheme as phase-merging enhanced harmonic generation (PEHG), further studies demonstrate that, this novel technique can be utilized for a real electron beam energy spread cooling in X-ray FEL linear accelerators [17]. Analytical estimates and 1D simulation results are given in Sec. III to present the physical mechanism of the phase-merging effect and the possibility of imprinting ultra-high harmonic microbunching into the electron beam with a relatively small energy spread using this technique.
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