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Title: Electron bunch acceleration in an inverse free-electron laser with a helical magnetic wiggler and axial guide field

Abstract

Electron bunch acceleration by a laser pulse having Gaussian radial and temporal profiles of intensity has been studied numerically in a static helical magnetic wiggler in vacuum. The main electron bunch parameters for simulations are 10 MeV initial energy with 0.1% longitudinal energy spread, 1 mm mrad rms transverse emittance, and 3x10{sup 12} cm{sup -3} density. It is shown that the radial Gaussian profile can decrease the acceleration gradient compared with that of the plane-wave approximation due to the reduction of electron-pulse interaction area. In order to collimate electron bunch and overcome the decreasing of the acceleration gradient, an external axial magnetic field is used. The importance of the electron initial phase with respect to laser pulse is considered, and some appropriate values are found. Finally, acceleration of a femtosecond (fs) microbunch with an optimum appropriate initial phase is considered, which leads to a nearly monoenergetic microbunch and an acceleration gradient of about {approx_equal}0.2 GeV/m.

Authors:
; ; ;  [1]
  1. Faculty of Basic Science, Department of Physics, Mazandaran University, Babolsar (Iran, Islamic Republic of)
Publication Date:
OSTI Identifier:
20860457
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 13; Journal Issue: 12; Other Information: DOI: 10.1063/1.2402508; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; 43 PARTICLE ACCELERATORS; ACCELERATION; ACCELERATORS; APPROXIMATIONS; BEAM BUNCHING; COMPUTERIZED SIMULATION; ELECTRONS; FREE ELECTRON LASERS; GEV RANGE; LIGHT TRANSMISSION; MAGNETIC FIELDS; MEV RANGE; NUMERICAL ANALYSIS; PLASMA; PLASMA GUNS; PULSES

Citation Formats

Mirzanejhad, Saeed, Sohbatzadeh, Farshad, Asri, Mehdi, and Toosi, Ershad Sadeghi. Electron bunch acceleration in an inverse free-electron laser with a helical magnetic wiggler and axial guide field. United States: N. p., 2006. Web. doi:10.1063/1.2402508.
Mirzanejhad, Saeed, Sohbatzadeh, Farshad, Asri, Mehdi, & Toosi, Ershad Sadeghi. Electron bunch acceleration in an inverse free-electron laser with a helical magnetic wiggler and axial guide field. United States. doi:10.1063/1.2402508.
Mirzanejhad, Saeed, Sohbatzadeh, Farshad, Asri, Mehdi, and Toosi, Ershad Sadeghi. Fri . "Electron bunch acceleration in an inverse free-electron laser with a helical magnetic wiggler and axial guide field". United States. doi:10.1063/1.2402508.
@article{osti_20860457,
title = {Electron bunch acceleration in an inverse free-electron laser with a helical magnetic wiggler and axial guide field},
author = {Mirzanejhad, Saeed and Sohbatzadeh, Farshad and Asri, Mehdi and Toosi, Ershad Sadeghi},
abstractNote = {Electron bunch acceleration by a laser pulse having Gaussian radial and temporal profiles of intensity has been studied numerically in a static helical magnetic wiggler in vacuum. The main electron bunch parameters for simulations are 10 MeV initial energy with 0.1% longitudinal energy spread, 1 mm mrad rms transverse emittance, and 3x10{sup 12} cm{sup -3} density. It is shown that the radial Gaussian profile can decrease the acceleration gradient compared with that of the plane-wave approximation due to the reduction of electron-pulse interaction area. In order to collimate electron bunch and overcome the decreasing of the acceleration gradient, an external axial magnetic field is used. The importance of the electron initial phase with respect to laser pulse is considered, and some appropriate values are found. Finally, acceleration of a femtosecond (fs) microbunch with an optimum appropriate initial phase is considered, which leads to a nearly monoenergetic microbunch and an acceleration gradient of about {approx_equal}0.2 GeV/m.},
doi = {10.1063/1.2402508},
journal = {Physics of Plasmas},
number = 12,
volume = 13,
place = {United States},
year = {Fri Dec 15 00:00:00 EST 2006},
month = {Fri Dec 15 00:00:00 EST 2006}
}
  • The motion of a relativistic electron is analyzed in the field configuration consisting of a constant-amplitude helical wiggler magnetic field, a uniform axial magnetic field, and the equilibrium self-electric and self-magnetic fields produced by the non-neutral electron beam. By generating Poincare surface-of-section maps, it is shown that the equilibrium self-fields destroy the integrability of the motion, and consequently part of phase space becomes chaotic. In particular, the Group I and Group II orbits can be fully chaotic if the self-fields are sufficiently strong. The threshold value of the self-field parameter {epsilon}={omega}{sup 2}{sub {ital pb}}/4{Omega}{sup 2}{sub {ital c}} for the onsetmore » of beam chaoticity is determined numerically for parameter regimes corresponding to moderately high beam current (and density). It is found that the characteristic time scale for self-field-induced changes in the electron orbit is of the order of the time required for the beam to transit one wiggler period. An analysis of the first-order, self-field-induced resonances is carried out, and the resonance conditions and scaling relations for the resonance width are derived. The analytical estimates are in good qualitative agreement with the numerical simulations.« less
  • A theory for gain in a free-electron laser with helical wiggler and axial magnetic field in the presence of self-fields is presented. It is found that for group I orbits, gain decrement is obtained relative to the absence of the self-fields, while for group II orbit gain enhancement is obtained. The gain decrement and enhancement are due to the diamagnetic and paramagnetic effects of the self-magnetic field, respectively.
  • The dispersion relation of a two-stream free-electron laser (TSFEL) with a one-dimensional helical wiggler and an axial magnetic field is studied. Also, all relativistic effects on the space-charge wave and radiation are considered. This dispersion relation is solved numerically to find the unstable interaction among the all wave modes. Numerical calculations show that the growth rate is considerably enhanced in comparison with single-stream FEL. The effect of the velocity difference of the two electron beams on the two-stream instability and the FEL resonance is investigated. The maximum growth rate of FEL resonance is investigated numerically as a function of themore » axial magnetic field.« less
  • Analytical formulas of the Larmor rotation are derived in detail for the equilibrium electrons motion in a free-electron laser with combination of a three-dimensional (3-D) helical wiggler and a positive or a reversed guide magnetic field. Generally, the Larmor radius in the configuration of a reversed guide field is much smaller than that in a positive guide field. At non-resonance, a helical orbit governed by the zero-order component of a 3-D wiggler field could hold; meanwhile, the higher-harmonic effect definitely influences those electrons with off-axis guiding centers and induces the electron-beam spreads. At resonance, the Larmor radius in the configurationmore » of a positive guide field has a singularity with a limit tending to infinite, which causes all the electrons to hit the waveguide wall before the exit of the wiggler. Although Larmor-radius singularity does not exist in the configuration of a reversed guide field, at anti-resonance, the first-order harmonic of a 3-D wiggler field induces a transverse displacement which rapidly grows in proportion to a square of time, and leads part of the electron beam to hit the waveguide wall before reaching the wiggler exit, which depends on the specific parameters of the individual electrons. The analytical conclusions derived in the present paper are examined by the nonlinear simulations and the experimental observation. Disagreement with the previous literatures is discussed in detail.« less
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