Influence of the trapped-electron distribution on the sideband instability in a helical wiggler free-electron laser

Yang, T. Y. B.; Davidson, Ronald C.

doi:10.1063/1.859511

Cited by 6 publications

(1 citation statement)

References 68 publications

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“…5. The parabolic and uniform distributions maintain an improved trapping and guiding and this sustains the growth in output power allowing them both to reach over 2 TW of power at z ¼ 200 m. Contributing to this disparity in peak output power are the detrimental effects of the sideband instability [17,18]. The flatter transverse profiles of the parabolic and uniform distributions mitigate more effectively the power losses and energy deposited in the sidebands than the transversely Gaussian beam.…”

Section: Simulation Resultsmentioning

confidence: 99%

Terawatt x-ray free-electron-laser optimization by transverse electron distribution shaping

Emma

Fang

et al. 2014

Phys. Rev. ST Accel. Beams

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We study the dependence of the peak power of a 1.5 Å Terawatt (TW), tapered x-ray free-electron laser (FEL) on the transverse electron density distribution. Multidimensional optimization schemes for TW hard x-ray free-electron lasers are applied to the cases of transversely uniform and parabolic electron beam distributions and compared to a Gaussian distribution. The optimizations are performed for a 200 m undulator and a resonant wavelength of λ r ¼ 1.5 Å using the fully three-dimensional FEL particle code GENESIS. The study shows that the flatter transverse electron distributions enhance optical guiding in the tapered section of the undulator and increase the maximum radiation power from a maximum of 1.56 TW for a transversely Gaussian beam to 2.26 TW for the parabolic case and 2.63 TW for the uniform case. Spectral data also shows a 30%-70% reduction in energy deposited in the sidebands for the uniform and parabolic beams compared with a Gaussian. An analysis of the transverse coherence of the radiation shows the coherence area to be much larger than the beam spotsize for all three distributions, making coherent diffraction imaging experiments possible.

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Section: Simulation Resultsmentioning

confidence: 99%

Terawatt x-ray free-electron-laser optimization by transverse electron distribution shaping

Emma

Fang

et al. 2014

Phys. Rev. ST Accel. Beams

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Measurements of the trapped particle sideband instability compared to the macroparticle model

Hartmann

Driscoll

2001

Physics of Plasmas

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The upper and lower sidebands are measured on a traveling wave tube where a cold electron beam is trapped by a large amplitude wave. The two strongly coupled sidebands form a normal mode that is characterized by the sideband growth rates, wave number shifts, amplitude ratio, and phase relationship. The measured values agree only qualitatively with the macroparticle model of Kruer, Dawson, and Sudan [Phys. Rev. Lett. 23, 838 (1969)]. Also, the macroparticle model prediction for a nonlinear product wave does not agree with the experiment. Quantitative agreement is found between the experiment and computer simulations that follow the electron orbits, suggesting that the trapped particle model is too simple for quantitative predictions.

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Macroclump model of the nonlinear evolution of the sideband instability in a helical wiggler free-electron laser

Yang

Davidson

1990

Physics of Fluids B: Plasma Physics

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The nonlinear evolution of a helical wiggler free electron laser is investigated within the framework of a macroclump model for the trapped electrons. The model describes the nonlinear evolution of a right-circularly polarized electromagnetic wave with frequency w, and wavenumber k,, and slowly varying amplitude &,(z, t) and phase 8 ,(z, t) (eikonal approximation). The model further assumes that the trapped electrons can be treated as tightly bunched macroclumps that interact coherently with the radiation field. The analysis is carried out in the ponderomotive frame, which leads to a substantial simplification in both the analytical and numerical studies. As a first application, the nonlinear evolution of the primary signal is examined when 98' = 0 (no spatial variation of the wave amplitude and phase). The evolution equations are reduced to quadrature, and the maximum excursion of the wave amplitude a,, is calculated analytically. Subsequently, the nonlinear evolution of the sideband instability is investigated, making use of the equations describing the self-consistent evolution of the wave amplitude &, and phase 8,, which vary slowly with both space and time, together with the macroclump orbit equation. In the present analysis, the sideband signals are treated as perturbations (not necessarily small) about a constant-amplitude (&0 = const) primary electromagnetic wave with slowly varying phase 6'(z'). The coupled orbit and field equations are investigated analytically and numerically over a wide range of system parameters to determine detailed scaling properties of the sideband instability. The results of the present analysis suggest that free electron lasers operating with system parameters corresponding to the strong-pump regime [(f'/I, )'/4 > 1] are least vulnerable to the sideband instability. Moreover, the nonlinear evolution of the sideband instability is investigated numerically for system parameters corresponding to the Los Alamos free electron laser experiment. In several aspects, the numerical results are found to be in good qualitative agreement with the experimental results.

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Influence of the trapped-electron distribution on the sideband instability in a helical wiggler free-electron laser

Cited by 6 publications

References 68 publications

Terawatt x-ray free-electron-laser optimization by transverse electron distribution shaping

Terawatt x-ray free-electron-laser optimization by transverse electron distribution shaping

Measurements of the trapped particle sideband instability compared to the macroparticle model

Macroclump model of the nonlinear evolution of the sideband instability in a helical wiggler free-electron laser

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