Model-based optimization of tapered free-electron lasers

Mak, A. A.; Curbis, Francesca; Werin, Sverker

doi:10.1103/physrevstab.18.040702

Cited by 24 publications

(17 citation statements)

References 9 publications

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“…In the KMR model, the undulator segment length required for the efficient deceleration of particles is L segm < min[L sync (z)], as discussed in Ref. [10]. In our phase jump model, the requirement is L segm < min[L sync (z)]/4, which is a more stringent one.…”

Section: Comparison With Undulator Taperingmentioning

confidence: 81%

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Phase jump method for efficiency enhancement in free-electron lasers

Mak

Curbis

Werin

2017

Phys. Rev. Accel. Beams

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The efficiency of a free-electron laser can be enhanced by sustaining the growth of the radiation power beyond the initial saturation. One notable method is undulator tapering, which involves the variation of the gap height and/or the period along the undulator. Another method is the introduction of phase jumps, using phase-shifting chicanes in the drift sections separating the undulator segments. In this article, we develop a physics model of this phase jump method, and verify it with numerical simulations. The model elucidates the energy extraction process in the longitudinal phase space. The main ingredient is the microbunch deceleration cycle, which enables the microbunched electron beam to decelerate and radiate coherently beyond the initial saturation. The ponderomotive bucket is stationary, and energy can even be extracted from electrons outside the bucket. The model addresses the selection criteria for the phase jump values, and the requirement on the undulator segment length. It also describes the mechanism of the final saturation. In addition, we discuss the similarities and differences between the phase jump method and undulator tapering, by comparing our phase jump model to the classic Kroll-Morton-Rosenbluth model.

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Section: Comparison With Undulator Taperingmentioning

confidence: 81%

“…Apart from the phase jump method, another common technique for FEL efficiency enhancement is undulator tapering, which involves the variation of the undulator parameter and/or the undulator period along the undulator line [9,10]. In Ref.…”

Section: Introductionmentioning

confidence: 99%

Phase jump method for efficiency enhancement in free-electron lasers

Mak

Curbis

Werin

2017

Phys. Rev. Accel. Beams

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“…Normally, the FEL saturation occurs as the power reaches a certain level with the qualities of electrons deteriorated severely, namely, the parameter relations of the electron beam and the optical field have deteriorated. To increase the FEL efficiency, an appropriate way is the use of a tapered undulator [2][3][4][5][6][12][13][14]. Around the FEL saturation, the undulator parameters are tapered along the undulator to maintain the resonant condition and the energy transfer from the electrons to the radiation.…”

Section: Introductionmentioning

confidence: 99%

“…The optimal taper strategy highly depends on the electron beam parameters and FEL parameters. The optimization of the taper profile typically relies on numerical simulations, such as multidimensional scanning schemes [12], the GINGER self-design taper algorithm [13], the modified KMR model [14], and so on.…”

Section: Introductionmentioning

confidence: 99%

Some analyses on optimal energy-extraction efficiency in a free-electron laser

Jia

2020

J. Phys. Commun.

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In this paper, the energy-extraction efficiencies of the electron beam are studied for several cases of free-electron laser (FEL). For an initially cold electron beam, the optimal initial detuning for the maximum energy-extraction efficiency and the corresponding saturation length are given. A scheme of the 'top up' is proposed to enhance the efficiency: after the electron energy being modulated somewhat, a phase shift and a step-down of the phase bucket are introduced, so that all electrons are located near the upper separatrix of the bucket in the phase space. Finally, the energy-extraction efficiency can be increased by 30% compared with that of the normal undulator case. For a linear tapering undulator with an initially cold electron beam, the simple scaling laws for the maximum energy-extraction efficiency and the corresponding optical power gain are obtained. For a tapered undulator with the pre-bunched electron beam, our analysis gives that the energy-extraction efficiency reaches the maximum when the phase bucket height of the tapered undulator is equal to the amplitude of the detuning modulation. The numerical results validated this reasoning and show that the efficiency has a large increase compared with the case of the unbunched electron beam. The single stair-step undulator is investigated, the optimal step and the corresponding saturation power and saturation length are given by analysis, they agree well with the numerical simulation results.

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“…The determination of the optimal taper profile has been addressed in numerous papers for a variety of configurations [17,[24][25][26][27][28], and neither a linear nor quadratic taper may be optimal for every configuration. Indeed, the optimal taper profile found in [17] varied with distance along the undulator by a power of 2.1.…”

Section: Introductionmentioning

confidence: 99%

Studies of a terawatt x-ray free-electron laser

Freund

Slot

2018

New J. Phys.

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The resolution in x-ray coherent diffractive imaging applications can be improved by increasing the number of photons in the optical pulse. An x-ray free-electron laser (XFEL) producing pulses with terawatt (TW) peak power and about 10 femtosecond duration can satisfy this requirement. In this paper, we consider the conditions necessary for achieving powers in excess of 1 TW in a 1.5 Å FEL. Using the MINERVA simulation code, an extensive steady-state analysis has been conducted using a variety of undulator and focusing configurations. In particular, strong focusing using FODO lattices is compared with the natural, weak focusing inherent in helical undulators. It is found that the most important requirement to reach TW powers is extreme transverse compression of the electron beam in a strong FODO lattice in conjunction with a tapered undulator. We find that when the current density reaches extremely high levels, that the characteristic growth length in the tapered undulator becomes shorter than the Rayleigh range giving rise to optical guiding. We also show that planar undulators can reach near-TW power levels. In addition, preliminary time-dependent simulations are also discussed and show that TW power levels can be achieved both for self-seeding and pure self-amplified spontaneous emission. This result shows that high-resolution, single molecule diffractive imaging may be realized using XFELs.

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Model-based optimization of tapered free-electron lasers

Cited by 24 publications

References 9 publications

Phase jump method for efficiency enhancement in free-electron lasers

Phase jump method for efficiency enhancement in free-electron lasers

Some analyses on optimal energy-extraction efficiency in a free-electron laser

Studies of a terawatt x-ray free-electron laser

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