Stability properties of free-electron laser in Raman regime with thermal electron beam

Chakhmachi, Amir; Maraghechi, B.

doi:10.1063/1.3106684

Cited by 9 publications

(17 citation statements)

References 26 publications

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“…1 One also observes that our approximation on the connection between momentum and velocity is limited by the magnitude of the initial velocity spread Dv 0 . However, given the narrow spreads in FELs, 13 the linear connection is fairly accurate. As we mention along the work, the present strategy based on the compressibility suggests a way to estimate the fraction of the electron population actively participating in the FEL interaction.…”

Section: Discussionmentioning

confidence: 99%

“…Given the simplicity and the reach of water bag distributions, at this point, we introduce our initial distribution function for electrons as a uniform water bag lying along the phase h, with a small half-width Dv 0 around an average injection velocity v 0 . We point out that due to the smallness of the velocity width, a very realistic assumption for FELs, 13 the connections between the widths in velocity, momentum, and energy spaces are approximately linear. Under the linearity condition, if the phase-space density is a constant in one representation, it is also constant in the others.…”

Section: B the Warm Fluid Modelmentioning

confidence: 99%

“…In terms of magnitude, it falls close-within a range of 6%-from calculations involving different kinds of distribution function. 13 Considering the importance of space-charge effects in many current devices, 16 in all cases investigated in this paper, we take g ¼ 0.03, unless otherwise stated, which places the system in a high-gain Raman regime, …”

Section: B the Warm Fluid Modelmentioning

confidence: 99%

See 2 more Smart Citations

Nonlinear model for thermal effects in free-electron lasers

2014

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In the present work, we extend results of a previous paper [Peter et al., Phys. Plasmas 20, 12 3104 (2013)] and develop a semi-analytical model to account for thermal effects on the nonlinear dynamics of the electron beam in free-electron lasers. We relax the condition of a cold electron beam but still use the concept of compressibility, now associated with a warm beam model, to evaluate the time scale for saturation and the peak laser intensity in high-gain regimes. Although vanishing compressibilites and the associated divergent densities are absent in warm models, a series of discontinuities in the electron density precede the saturation process. We show that full wave-particle simulations agree well with the predictions of the model. V C 2014 AIP Publishing LLC. [http://dx

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Section: Discussionmentioning

confidence: 99%

Section: B the Warm Fluid Modelmentioning

confidence: 99%

Section: B the Warm Fluid Modelmentioning

confidence: 99%

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Nonlinear model for thermal effects in free-electron lasers

2014

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“…16 Effects of independent parallel and perpendicular velocity spread on lasing wavelength were also evaluated and compared. 10 Dispersion relation was obtained to describe FEL stability properties 8,17 or study thermal properties of a plasma-loaded FEL 18 with axially warm electron beam. The nonlinear evolution of FEL in which the electron beam propagates with energy spread has also been investigated numerically.…”

Section: Introductionmentioning

confidence: 99%

Efficiency enhancement of nonlinear odd harmonics in thermal free electron laser

Bazouband

Maraghechi

2013

Journal of Applied Physics

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The effect of axial energy spread on the radiation of third harmonic is studied in the free electron laser with planar wiggler and ion-channel guiding. Spread in the longitudinal momentum and so in the initial energy of electron beam, without any spread in the transverse velocity, is assumed in the form of Gaussian distribution function. The technique that is employed is a one-dimensional and steady-state simulation. A set of self consistent nonlinear differential equations that describes the system is solved numerically by Runge-Kutta method. Due to the sensitivity of harmonics to thermal effects, gain improvement of third harmonic radiation is achieved by using ion-channel guiding technique and efficiency enhancement is applied by tapering the magnetic field of wiggler to optimize radiation. The bunching parameter of the electron beam is also studied. It is found that the growth of the magnitude of the bunching parameter that is caused by the ponderomotive wave stops before the saturation point of the radiation. This means that ponderomotive wave saturates at a shorter distance compared to the radiation.

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“…23, in context of kinetic theory, the analytical expression for linear growth rate under weak resonant instability condition in the Raman regime was investigated. In that work, thermal effects on linear growth rate in both the Raman and the Compton regime were studied.…”

Section: Introductionmentioning

confidence: 99%

Influence of space charge wave on quasilinear theory of the free-electron laser saturation

Chakhmachi

Maraghechi

2009

Physics of Plasmas

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A quasilinear theory is presented that describes the self-consistent evolution of the electron beam distribution function and fields in a free-electron laser when the space charge wave is present. In the Raman regime, a high-density electron beam has an appreciable space charge potential. A broad spectrum of waves is assumed in order to have a relatively wide range of resonant particles. A one-dimensional helical magnetic field is considered and the analysis is based on the Vlasov-Maxwell equations. Two coupled differential equations are derived, which, in conjunction with conservation laws, describe the quasilinear development by the diffusion of electrons in the momentum space. This leads to the saturation of the free-electron laser instability by the plateau formation. Analytical expressions for the growth rate and for the diffusion coefficient are derived, which reduced to those in the Compton regime under appropriate conditions. By use of the linear growth rate and diffusion coefficient, an analytical expression for efficiency in Raman regime was derived. A numerical analysis is conducted to study the effects of the spectral width of radiation and the thermal spread of the electron beam on the efficiency.

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Stability properties of free-electron laser in Raman regime with thermal electron beam

Cited by 9 publications

References 26 publications

Nonlinear model for thermal effects in free-electron lasers

Nonlinear model for thermal effects in free-electron lasers

Efficiency enhancement of nonlinear odd harmonics in thermal free electron laser

Influence of space charge wave on quasilinear theory of the free-electron laser saturation

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