skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Mode couplings in a two-stream free-electron laser with a helical wiggler and an ion-channel guiding

Abstract

In this study, the method of perturbation has been applied to obtain the dispersion relation (DR) of a two-stream free-electron laser (FEL) with a helical wiggler and an ion-channel with all relativistic effects on waves. This DR has been solved numerically to find the unstable modes and their growth rate. Numerical solutions of DR show that the growth rate is considerably enhanced in comparison with single-stream free-electron laser. In group II orbits, with relatively large wiggler induced velocities, new couplings are found. The effect of the velocity difference of the two electron beams on the instabilities has also been investigated in this study. Moreover, the effect of the ion-channel density on the maximum growth rate of FEL resonance has been analyzed.

Authors:
;  [1]
  1. Department of Physics, Faculty of Basic Sciences, University of Mazandaran, Babolsar (Iran, Islamic Republic of)
Publication Date:
OSTI Identifier:
22303763
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 21; Journal Issue: 8; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; COMPARATIVE EVALUATIONS; COUPLINGS; DISPERSION RELATIONS; ELECTRON BEAMS; FREE ELECTRON LASERS; NUMERICAL SOLUTION; PERTURBATION THEORY; RELATIVISTIC RANGE; STREAMS

Citation Formats

Mohsenpour, Taghi, E-mail: mohsenpour@umz.ac.ir, and Alirezaee, Hajar. Mode couplings in a two-stream free-electron laser with a helical wiggler and an ion-channel guiding. United States: N. p., 2014. Web. doi:10.1063/1.4892958.
Mohsenpour, Taghi, E-mail: mohsenpour@umz.ac.ir, & Alirezaee, Hajar. Mode couplings in a two-stream free-electron laser with a helical wiggler and an ion-channel guiding. United States. doi:10.1063/1.4892958.
Mohsenpour, Taghi, E-mail: mohsenpour@umz.ac.ir, and Alirezaee, Hajar. 2014. "Mode couplings in a two-stream free-electron laser with a helical wiggler and an ion-channel guiding". United States. doi:10.1063/1.4892958.
@article{osti_22303763,
title = {Mode couplings in a two-stream free-electron laser with a helical wiggler and an ion-channel guiding},
author = {Mohsenpour, Taghi, E-mail: mohsenpour@umz.ac.ir and Alirezaee, Hajar},
abstractNote = {In this study, the method of perturbation has been applied to obtain the dispersion relation (DR) of a two-stream free-electron laser (FEL) with a helical wiggler and an ion-channel with all relativistic effects on waves. This DR has been solved numerically to find the unstable modes and their growth rate. Numerical solutions of DR show that the growth rate is considerably enhanced in comparison with single-stream free-electron laser. In group II orbits, with relatively large wiggler induced velocities, new couplings are found. The effect of the velocity difference of the two electron beams on the instabilities has also been investigated in this study. Moreover, the effect of the ion-channel density on the maximum growth rate of FEL resonance has been analyzed.},
doi = {10.1063/1.4892958},
journal = {Physics of Plasmas},
number = 8,
volume = 21,
place = {United States},
year = 2014,
month = 8
}
  • A linear theory of two-stream free electron laser (FEL) with helical wiggler and ion channel guiding is presented. The dispersion relation is obtained with the help of fluid theory and the growth rate is analyzed through the numerical solutions. The considerable enhancement of the growth rate is demonstrated due to the two-stream instability and continuous tuning of peak growth rate ratio, two-stream FEL compared to single-stream FEL, in terms of varying the ion channel frequency is illustrated.
  • A theory is developed for a free-electron laser (FEL) with a three-dimensional helical wiggler and ion-channel guiding. The relativistic equation of motion for a single electron in the combined wiggler and ion-channel fields is solved in the rotating wiggler frame. With the aid of the conservation of energy, equations for the axial velocity and the {phi} function (which determines the rate of change of axial velocity with energy) are studied numerically. An analysis of the electromagnetic radiation copropagating with the electron beam in the FEL interaction region is also presented. The gain formula is derived and calculations indicate that themore » gain of the realizable wiggler is considerably greater than the gain of the idealized one, and the gain enhancement increases with increasing wiggler magnetic field. It is shown that the gain for group-I orbits is positive, while for group-II orbits, the gain is negative in the negative mass regime (i.e., {phi}<0) and positive in the positive mass regime.« less
  • The dispersion relation for a free-electron laser (FEL) with a one-dimensional helical wiggler and an ion channel, in the collective regime, is found with all relativistic effects on the space-charge wave and radiation included. This dispersion relation is solved numerically to study the unstable interaction among all wave modes. In group I orbits, coupling between the positive-energy space-charge wave and the left circularly polarized electromagnetic wave is found. This instability and the coupling between the negative and positive-energy space-charge wave are found in the group II orbits in the negative mass regime. In group II orbits, there is a couplingmore » between the right and left circularly polarized electromagnetic waves, in the positive mass regime. These instabilities are found to be distinct from the main FEL resonance. Contrary to the main FEL resonance, the additional instabilities have a nonrelativistic nature and are made of strongly coupled modes.« less
  • A method for efficiency enhancement in free-electron laser is studied which uses both tapered wiggler magnetic field and ion-channel density. Derivation of a set of nonlinear and coupled differential equations leads to the self-consistent description of the evolution of both an ensemble of electrons and the electromagnetic radiation. Numerical solution of these equations reveals considerable enhancements of the interaction efficiency. In order to obtain a better insight into physical basis of the problem, a modified pendulum equation for the interaction is derived and a small signal theory of the efficiency enhancement is developed.
  • Deformation of steady-state trajectories of an electron, due to transverse inhomogeneity in a realizable three-dimensional helical wiggler field with ion-channel guiding, is studied. The {phi} function that determines the rate of change of axial velocity with energy is derived and shows that transition to negative mass regime remains approximately unchanged under the influence of the three-dimensional effect of the wiggler. A detailed stability analysis of orbits is performed, with variation in relativistic factor {gamma} included in the formalism, and a new stable branch is found for group-II orbit. Finally a formula for the small signal gain is derived with radiationmore » forces in transverse components of the equation of motion included and results are compared with previous works in one-dimensional case.« less