Helical Wiggler Magnetic Field Research Articles

Electron bunch acceleration by an azimuthally polarized laser pulse in the presence of a helical wiggler and external magnetic field

This study investigates the acceleration of a single electron and an electron bunch by an azimuthally polarized (AP) laser pulse in the presence of a helical wiggler and external magnetic field in the form of a hyperbolic tangent (HT) function. The wiggler parameters were optimized to retain betatron resonance for a long time, as a result of which it was found that the optimum values of HT magnetic field strength and its parameter increase the interaction length. The laser fields, the wiggler magnetic field, and the HT magnetic field cooperatively helped cause the generation of the high energetic electrons. Finally, highly energetic electrons were obtained with a mean energy of about 2 GeV and an extremely low mean scattering angle of [Formula: see text], and an acceleration gradient of about 42 GeV/m.

Investigation of electron acceleration in vacuum by a radially polarized laser pulse in the presence of helical wiggler field and axial magnetic field guiding

In this paper, electron acceleration by a radially polarized laser pulse in the presence of helical wiggler magnetic field and axial magnetic field has been studied. The governing equations on electron dynamics in the presence of these electric and magnetic fields were solved by the fourth order Runge-Kuta method. The effect of axial magnetic field and electron injection angle on energy gained by the electron was investigated. Numerical studies have shown that the final energy of an electron depends on the value of the magnetic field and the injection angle. It was seen that by applying a magnetic field of about 0.2 and the injection angle of about 11 degrees, the electron can gain final energy of about 3.8 GeV, which is 40 percent more than the case of zero degrees injection angle and the absence of external magnetic field.

Trajectories in relativistic electron beam with elliptical cross section under the effects of self-fields, axial, planar and helical wiggler magnetic fields

The influence of axial magnetic field and self-fields in the electron gas column and electron beam with elliptical cross section is investigated. Further effects of cross section demotions and beam velocity on the electron rotating frequency are studied. It is shown that there are two solutions of fast and slow for electron rotating frequency. The obtained results are graphically presented. Besides the effects of axial magnetic field, self-fields, both planar wiggler magnetic field (PWMF) and helical wiggler magnetic field (HWMF) on trajectories of relativistic electron beam with elliptical cross section are investigated. By solving the motion equation for an electron in the considered fields, two equations for the average axial velocity and the function Φ are calculated. The effects of elliptical cross section demotions and elliptical electron beam density are studied. The effects of cross-section demotions and elliptical electron beam density are graphically investigated and so the results are compared for elliptical and circular electron beams. It is shown that with decreasing of value of electron beam density transverse velocity of electron increases about .

Enhancement of Gain and Modified Electron Beam Trajectories Using a Relativistic Electron Beam With an Elliptical Cross Section in Free-Electron Laser With a Helical Wiggler and Ion-Channel Guiding

This article investigates the effects of ion-channel guiding, axial magnetic fields, helical wiggler magnetic fields (HWMFs), and self-fields on trajectories of the elliptical relativistic electron beam. Two equations for the average axial velocity and the function $\Phi $ are calculated for an electron in the considered fields by solving the motion equation. In the meantime, the effects of elliptical cross section demotions and elliptical electron beam density are also studied. The results are compared in the limit that the elliptical electron beam is converted to a circular electron beam, which have also been graphically presented. It is shown that in the considered conditions, in the case of the elliptical beam, and for spatial cases, there are three types of trajectories. This result is different from the case circular beam because in the case circular beam, there are two types of trajectories. It means that in the case of the elliptical cross section, there are two resonance frequencies of the orbits. Moreover, the resonant frequency of the transverse velocity in the circular beam case is within two resonant frequencies in the elliptical beam case. Furthermore, it has been indicated that for special cases, with increasing $\bar {\omega }_{p} $ , the resonance frequencies of transverse velocity tend toward higher values of $\bar {\omega }_{i} $ . Finally, the conditions of stability of electron orbits in the elliptical electron beam are investigated by considering HWMF. Furthermore, a detailed analysis of the gain equation in an FEL with elliptical electron beam is presented. The obtained gain for an FEL together with a relativistic electron beam with elliptical cross section is compared to the maximum gain for an FEL together with a relativistic electron beam with circular cross section. It is shown that with increasing the ratio of the semimajor to semiminor axes of the beam cross section, the ratio of the gain of the elliptical electron beam increases compared to when a circular electron beam is used for the group I orbits, while for group II orbits the gain decreased, but in special conditions for group II orbits the gain increased. We investigated a study more precisely on the stability of electron orbits of this free-electron laser in the Appendix.

Controlling polarization of THz radiation in pair plasma

Polarization-tunable terahertz (THz) radiation in pair plasma has been generated under the combined configuration of a helical wiggler and solenoidal magnetic fields. The control over the electromagnetic vector of the emitted field (i.e. polarization) furnishes the knob of another degree of freedom which is very useful in numerous applications. With the optimization of wiggler period and frequency, the total angular spread of the field has been reduced which provides a narrow-band THz spectrum. Additionally, the solenoidal field not only prevents the escape of particles during laser-matter interaction but also enhances the magnitude of emitted field. Along with the external magnetic field, collisions among the particles and ripples in plasma density have also been considered to fine-tune the radiation.

Electron Energy Gain in laser ion channel affected by the space-charge potential and helical wiggler and external uniform magnetic fields

Electron Energy Gain in laser ion channel affected by the space-charge potential and helical wiggler and external uniform magnetic fields

Effect of beam prebunching on saturation characteristics of Raman free electron laser with helical wiggler and axial magnetic field

Abstract In this paper, amplification and saturation properties of one dimensional free electron laser (FEL) operating in Raman regime with helical wiggler and axial magnetic field are studied. In order to investigate and enhance the saturation characteristics of the system, prebunched electron beam is considered which describes the non-uniform initial distribution of the electrons. By using Maxwell’s equations and Lorentz force equation of motion of the beam, a set of self-consistently coupled nonlinear differential equations, describing radiation dynamics and beam trajectories, is derived and is solved numerically by the fourth order Runge–Kutta method. To study the effect of the beam prebunching on the saturation, the linear and non-linear initial distribution of the electrons are considered. Depending on the strength of the axial field, it is found that beam prebunching can reduce the saturation length and enhance the saturation efficiency of the radiation field substantially which can be offered as an effective approach to bring down the cost of the FEL system.

The Gain Equation of a Helical Wiggler Free Electron Laser with Ion-Channel Guiding and/or an Axial Magnetic Field

Electron motion in the combined ion-channel, helical wiggler and axial magnetic fields is analyzed in the absence of a radiation field. Detailed analysis of the gain equation in a free-electron laser is presented. Numerical calculations are made to illustrate the effects of the two electron-beam guiding devices on the gain when applied separately and simultaneously.

Three-dimensional nonlinear efficiency enhancement analysis in free-electron laser amplifier with prebunched electron beam and ion-channel guiding

Efficiency enhancement in free-electron laser is studied by three-dimensional and nonlinear simulation using tapered helical wiggler magnetic field or tapered ion-channel density. In order to reduce the saturation length, prebunched electron beam is used. A set of nonlinear and coupled differential equations are derived that provides the self-consistent description of the evolution of both an ensemble of electrons and the electromagnetic radiation. These equations are solved numerically to show that the combined effect of tapering and prebunching results in significant enhancement of power and considerable reduction of the saturation length. To have a deeper insight into the problem, an analytical treatment is also presented that uses the small signal theory to derive a modified pendulum equation.

Linear theory of magnetized ion-channel free-electron laser

A theory of wiggler pumped ion-channel free-electron laser (WPIC-FEL) and an axial magnetic field is presented. The motion of a relativistic electron is analyzed in the field configuration consisting of a helical wiggler magnetic field, a uniform axial magnetic field, and an electrostatic electric field produced by an ion-channel. An equation for the function Φ, which determines the rate of change of axial velocity with energy, is derived. Numerical calculations are made to illustrate the effects of two electron beam guiding devices on the trajectories. By means of linear fluid theory, the sixth-degree polynomial dispersion equation for electromagnetic and space-charge waves is derived. The dependence of growth rate-frequency curves on the ion-channel frequency and axial magnetic field is studied numerically.

Influence of self-fields on coupled waves in free electron laser with ion-channel guiding

In this study, the equilibrium orbits and their stability, under the influence of self-electric and self-magnetic fields, are analyzed. A dispersion relation for the Raman regime free electron laser with a helical wiggler magnetic field and ion-channel guiding is derived and analyzed, taking into account self-field effects of the electron beam. This dispersion relation is solved numerically to study unstable couplings between all wave modes. New unstable orbits, in the first part of the group I orbits and in the resonance region of the group II orbits, are found. It was found that self-fields reduce the growth rate of the group I orbits and increase it in the group II orbits.

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

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.

Chaotic electron trajectories in a realizable helical wiggler with axial magnetic field

Chaotic behavior of relativistic electron motion in a free-electron laser with realizable helical wiggler and axial magnetic field is investigated by using Pioncaré maps and Liapunov exponents. It is shown that in the presence of low to medium axial magnetic field, the motion of the electron may be chaotic. The effect of high axial magnetic field on electron dynamics causes the motion to become regular and nonchaotic. The chaotic behavior of electron motion in the absence of self-fields and axial magnetic field is due to the spatial inhomogeneities of the realizable helical wiggler magnetic field.

Self-fields in a free-electron laser with helical wiggler and axial magnetic field

An analysis of self-fields associated with charge and current densities of the electron beam in a free-electron laser with helical wiggler and axial magnetic field is presented. The self-electric field is derived from Poisson's equation. A more detailed analytical model for the self-magnetic field is determined from Ampere's law. Mutual influence of the electron velocity and self-magnetic field is considered to account for the total self-magnetic field. It is shown that for group I orbits, the self-magnetic field acts as a diamagnetic correction to the wiggler magnetic field; for group II orbits, it acts as a paramagnetic correction. Both diamagnetic and paramagnetic effects become stronger near the transverse velocity resonance. An important effect of the self-fields on the electron trajectories is the creation of unstable orbits for group II, which are not found in the absence of self-fields.

Response to “Comment on ‘Relativistic Raman backscattering theory with application in free-electron lasers with helical wiggler and axial magnetic field’ ” [Phys. Plasmas 12, 014701 (2005)

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Comment on “Relativistic Raman backscattering theory with application in free-electron lasers with helical wiggler and axial magnetic field” [Phys. Plasmas 11, 4483 (2004)

The shortcomings of the dispersion relation in Kordbacheh et al. [Phys. Plasmas 11, 4483 (2004)] are pointed out, and an improved general dispersion relation for free-electron lasers with helical wigglers and axial magnetic fields is presented.

Relativistic Raman backscattering theory with application in free-electron lasers with helical wiggler and axial magnetic field

A relativistic theory for Raman backscattering, in the beam frame of electrons, is presented and is used to find the growth rate of a free-electron laser in Raman regime. The effects of the self-electric and self-magnetic fields, on the equilibrium trajectories of electrons, are taken into account. The wiggler effects, on the linear dispersion relations of the space-charge wave and radiation, are included in the analysis. A numerical computation is conducted to investigate the wiggler and self-field effects on the growth rate. The results of the relativistic and nonrelativistic treatments are compared.

Three-dimensional Raman free electron laser in a waveguide with annular electron beam

A linear theory for a free electron laser with a three-dimensional helical wiggler and axial magnetic field in the collective regime is presented. The configuration consists of an annular electron beam propagating inside a cylindrical waveguide. Parametric decay of the wiggler pump wave, in the beam frame, into a space-charge wave and an electric-magnetic waveguide mode is analyzed in three dimensions. A nonlinear wave equation for the three-wave interaction is derived and employed to obtain a formula for the spatial growth rate of the excited eigenmodes. Numerical analysis is conducted to study the growth rate, radiation wavelength, and required relativistic factor as functions of axial magnetic field B0. Variation of growth rate with the beam thickness and the radius of the equilibrium trajectory was also studied.

Linear Theory of Free Electron Laser with a Plasma-Loaded Cylindrical Waveguide

The dispersion characteristics of plasma–loaded free-electron laser has been analyzed using linear fluid model. The device under consideration consists of the cylindrical metallic waveguide, completely filled with background plasma and a relativistic electron beam which passes through a helical wiggler magnetic field. The result predicts that reasonable plasma density tends to improve the growth rate of the low-frequency optical wave of FEL and causes an shiftup in the operating frequency, However it has little effect on the growth rate of the high-frequency wave. In the plasma–loaded FEL, for the FEL oscillator, it may be tuned by varying the plasma density; and for the FEL amplifier, the wider frequency bandwidth is gained. A critical density ncp for the background plasma density is found.

Re-examination of the one-dimensional theory of a Raman free-electron laser

A new one-dimensional analysis of the collective interaction in a free-electron laser with combined helical wiggler and uniform axial magnetic fields is presented. Maxwell's curl relations and the cold-fluid equations are employed, with the appropriate form of solution for right and left circularly polarized electromagnetic waves and space-charge waves. A set of three linear homogeneous algebraic equations for the electric field amplitudes of the three propagating waves is derived. This set may be employed to obtain the general dispersion relation in the form of a tenth-degree polynomial equation. With the left circular wave assumed to be nonresonant, the dispersion relation reduces to a seventh-degree polynomial equation corresponding to four space-charge modes and three right circular modes. The results of a numerical study of the spatial growth rate and radiation frequency are presented.