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Title: Self-fields effects on gain in a free-electron laser with helical wiggler and axial magnetic field

Abstract

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.

Authors:
;  [1];  [2]
  1. Department of Physics, Iran University of Science and Technology, Narmak, Tehran 16844 (Iran, Islamic Republic of)
  2. (United States)
Publication Date:
OSTI Identifier:
20974887
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 3; Other Information: DOI: 10.1063/1.2435623; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; FREE ELECTRON LASERS; GAIN; MAGNETIC FIELDS; ORBITS; PARAMAGNETISM; WIGGLER MAGNETS

Citation Formats

Esmaeilzadeh, Mahdi, Willett, Joseph E., and Department of Physics and Astronomy, University of Missouri-Columbia, Columbia, Missouri 65211. Self-fields effects on gain in a free-electron laser with helical wiggler and axial magnetic field. United States: N. p., 2007. Web. doi:10.1063/1.2435623.
Esmaeilzadeh, Mahdi, Willett, Joseph E., & Department of Physics and Astronomy, University of Missouri-Columbia, Columbia, Missouri 65211. Self-fields effects on gain in a free-electron laser with helical wiggler and axial magnetic field. United States. doi:10.1063/1.2435623.
Esmaeilzadeh, Mahdi, Willett, Joseph E., and Department of Physics and Astronomy, University of Missouri-Columbia, Columbia, Missouri 65211. Thu . "Self-fields effects on gain in a free-electron laser with helical wiggler and axial magnetic field". United States. doi:10.1063/1.2435623.
@article{osti_20974887,
title = {Self-fields effects on gain in a free-electron laser with helical wiggler and axial magnetic field},
author = {Esmaeilzadeh, Mahdi and Willett, Joseph E. and Department of Physics and Astronomy, University of Missouri-Columbia, Columbia, Missouri 65211},
abstractNote = {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.},
doi = {10.1063/1.2435623},
journal = {Physics of Plasmas},
number = 3,
volume = 14,
place = {United States},
year = {Thu Mar 15 00:00:00 EDT 2007},
month = {Thu Mar 15 00:00:00 EDT 2007}
}
  • 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
  • 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 externalmore » 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.« less
  • 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
  • The small-signal gain for an electromagnetically pumped free-electron laser is calculated for an amplifier configuration which includes an axial-guide magnetic field. The large-amplitude electromagnetic wave acts like the magnetostatic wiggler in a conventional free-electron laser, and the expression for the gain is shown to reduce to the well-known result in the limit of a magnetostatic wiggler. Substantial enhancements in the gain are found when ..cap omega../sub 0/approx. =..gamma../sub 0/(..omega../sub w/+k/sub w/v/sub X/), where ..cap omega../sub 0/ is the axial gyrofrequency, ..gamma../sub 0/ is the relativistic factor for the electron beam, v/sub X/ is the axial velocity of the electron beam,more » and (..omega../sub w/,k/sub w/) are the frequency and wave vector of the electromagnetic wiggler.« less
  • The dynamics of a relativistic electron in the field configuration consisting of a constant-amplitude helical-wiggler magnetic field, a uniform axial magnetic field, and the equilibrium self-fields is described by a near-integrable three-degree-of-freedom Hamiltonian system. The system is solved asymptotically for small {epsilon} by the method of averaging, where {epsilon} measures the strength of the self-fields. Because the Hamiltonian does not depend on one of the coordinates, it immediately reduces to a two-degree-of-freedom system. For {epsilon}=0, this reduced system is integrable, but is not in standard form. The action-angle transformation to standard form is derived explicitly in terms of elliptic functions,more » thus enabling the application of the averaging procedure. For almost all regular electron trajectories the solution is explicitly derived in asymptotic form and an adiabatic invariant is constructed, both results are in a form that remains uniformly valid over the time interval for electrons to transit the laser. The analytical results are verified by numerical calculations for an example problem. {copyright} {ital 1996 American Institute of Physics.}« less