Wiggler Magnetic Field Research Articles

Wiggler magnetic field assisted second harmonic generation in clusters

Wiggler magnetic field assisted second harmonic generation in clusters has been investigated theoretically. An intense short-pulse laser propagating through a gas embedded with atomic clusters, converts it into hot plasma balls. For clusters with radius less than one tenth of the laser wavelength, the nonlinear restoration force dominates, which leads to second harmonic generation. The magnetic wiggler provides the uncompensated momentum to second harmonic photon, to make the process of harmonic generation resonant. We explore the impact of laser intensity and cluster size on the efficiency of second harmonic generation. Pulse slippage of second harmonic pulse out of the domain of fundamental laser pulse has been observed on account of group velocity mismatch between the fundamental and second harmonic pulse. Enhancement in the efficiency of the second harmonic is seen for the optimum values of wiggler magnetic field.

Resonant second harmonic generation in plasma by self-focused twisted beam

The resonant second harmonic generation in the presence of a wiggler magnetic field by twisted laser plasma interaction is surveyed. The wiggler magnetic field provides additional momentum required for the phase matching. The Laguerre–Gaussian modes can be used to control the self-focusing and improve the second harmonic generation in laser plasma interaction. The wave equations for the fundamental and the second harmonic fields have been solved in the paraxial approximation. The generation of the second harmonic considering self-focusing is investigated. Also, the dependence of the second harmonic power on the propagation distance for different values of initial fundamental beam intensity, vortex charge number of the doughnut main beam and plasma density has been obtained.

Analysis of electron dynamics and two mechanisms in a coaxial magnetic wiggler

The electron dynamics in a coaxial magnetic wiggler are analyzed numerically and studied in particle-in-cell (PIC) simulation. Electrons wiggle in angular direction to coherently generate a TE01 mode, and the results are consistent with each other. The trajectory of the electron in 3-D space and the effects on the trajectories of the initial phases of wiggler magnetic fields are researched, which helps to choose appropriate initial phases to control the trajectory of the electron. An oscillator of FEL with a coaxial magnetic wiggler based on a quasi cavity is designed for efficiently generating the TE01 mode with the high saturation power and high efficiency. The advantages of the quasi cavity structure are analyzed and the parameter-selection rules are investigated. Based on the electron dynamics, the process of electron bunching in the self amplified spontaneous emission (SASE) and the Seeded mechanisms are studied. The Seeded mechanism could accelerate electron bunching greatly and reduce the saturation time than the SASE by half.

Linear theory of quantum two-stream instability in a magnetized plasma with a transverse wiggler magnetic field

AbstractA fluid description is used to study the properties of two-stream instability due to interaction of a non-relativistic electron beam with quantum magnetized plasma and transverse wiggler magnetic field. It is assumed that the background plasma provides charge and current neutralization of the electron beam. The dispersion relation is obtained by solving and linearizing fluid-Maxwell equations. The resulting dispersion equation is analyzed numerically over a wide range of system parameters. The results of quantum and classical treatments are compared numerically, with including the effects of wiggler on the dispersion relation. It is found that the transverse wiggler magnetic field can strongly improve the instability of quantum plasma as well as classical plasma.

Feasibility of the Spin-Light Polarimetry Technique for Longitudinally Polarized Electron Beams

A novel polarimeter based on the asymmetry in the spacial distribution of synchrotron radiation will make for a fine addition to the existing M{\o}ller and Compton polarimeters. The spin light polarimeter consists of a set of wiggler magnet along the beam that generate synchrotron radiation. The spacial distribution of synchrotron radiation will be measured by ionization chambers. The up-down (below and above the wiggle) spacial asymmetry in the transverse plain is used to quantify the polarization of the beam. As a part of the design process, effects of a realistic wiggler magnetic field and an extended beam size were studied. The perturbation introduced by these effects was found to be negligible. Lastly, a full fledged GEANT-4 simulation was built to study the response of the ionization chamber.

Efficiency enhancement of nonlinear odd harmonics in thermal free electron laser

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.

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.

Effect of wiggler harmonics in a free-electron laser oscillator

We have analyzed multi-wiggler harmonics in a free-electron laser oscillator with a single laser harmonic. The wiggler magnetic field is expanded into first and higher harmonics, and the radiation field is decomposed into higher order modes. Comparative studies of the radiation output, and of the phase and energy of the first and higher wiggler harmonics that were done using a 3D FEL code that we have developed are presented.

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.

Magnetic wiggler-assisted third-harmonic generation of a Gaussian laser pulse in plasma

A Gaussian laser pulse propagating through plasma in the presence of a magnetic wiggler produces third-harmonic radiation. The wiggler's magnetic field provides additional momentum required for phase matching. The required wiggler wave number is sensitive to pulse duration and amplitude. The efficiency of the process is significant at the instant at which the phase matching condition is satisfied.

Electron acceleration in the inverse free electron laser with a helical wiggler by axial magnetic field and ion-channel guiding

Electron acceleration in the inverse free electron laser (IFEL) with a helical wiggler in the presence of ion-channel guiding and axial magnetic field is investigated in this article. The effects of tapering wiggler amplitude and axial magnetic field are calculated for the electron acceleration. In free electron lasers, electron beams lose energy through radiation while in IFEL electron beams gain energy from the laser. The equation of electron motion and the equation of energy exchange between a single electron and electromagnetic waves are derived and then solved numerically using the fourth order Runge-Kutta method. The tapering effects of a wiggler magnetic field on electron acceleration are investigated and the results show that the electron acceleration increases in the case of a tapered wiggler magnetic field with a proper taper constant.

Analysis of self-amplified spontaneous emission free-electron laser using Lienard-Wiechert fields

Dynamical equations of electrons in an electron beam with finite length under the influence of a planar wiggler magnetic field and the Lienard-Wiechert fields of other electrons are derived and solved numerically. The analysis is applicable to self-amplified spontaneous emission free-electron laser for which no initial seed radiation is required. By assuming a monoenergetic and filamentary electron beam, thermal effects are neglected and electrons are injected with zero average transverse distance from the wiggler axis. The formalism is based on the retardation effects; therefore, slippage is naturally embedded in the analysis. It was found that energy, number density, and two-particle correlation for the electron beam are modulated by the radiation wavelength which indicates bunching. Spatial, temporal, and angular characteristics of electromagnetic radiation power are also studied.

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.

Resonant third-harmonic generation of a short-pulse laser from electron-hole plasmas

In semiconductors, free carriers are created in pairs in inter-band transitions and consist of an electron and its corresponding hole. At very high carrier densities, carrier-carrier collisions dominate over carrier-lattice collisions and carriers begin to behave collectively to form plasma. Here, we apply a short-pulse laser to generate third-harmonic radiation from a semiconductor plasma (electron-hole plasma) in the presence of a transverse wiggler magnetic-field. The process of third-harmonic generation of an intense short-pulse laser is resonantly enhanced by the magnetic wiggler, i.e., wiggler magnetic field provides the necessary momentum to third-harmonic photons. In addition, a high-power laser radiation, propagating through a semiconductor imparts an oscillatory velocity to the electrons and exerts a ponderomotive force on electrons at the third-harmonic frequency of the laser. This oscillatory velocity produces a third-harmonic longitudinal current. And due to the beating of the longitudinal electron velocity and the wiggler magnetic field, a transverse third-harmonic current is produced that drives third-harmonic electromagnetic radiation. It is finally observed that for a specific wiggler wave number value, the phase-matching conditions for the process are satisfied, leading to resonant enhancement in the energy conversion efficiency.

Efficiency enhancement in free-electron laser amplifier with one dimensional helical wiggler and ion-channel guiding

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.

Frequency Transformer: Appropriate and Different Models for a Building-up and Collapsing Magnetoplasma Medium

The interaction of an electromagnetic wave with a time varying medium is governed by the property of conservation of the wavenumber. This property can be utilized to construct a frequency transformer. The time variation in the relative permittivity of the medium is easily produced in a magnetoplasma medium by altering the ionization level. The change of the ionization level can be produced by the dynamic control of the source of ionization. The switching-on action of the source produces a build-up plasma, whereas a switching-off action produces a decaying plasma. Simple mathematical models, however, for the two cases are different. In the case of building-up plasma, the model has to ensure the continuity of the current density and in the case of decaying plasma, the average drift velocity of the surviving electrons has to be continuous. Using these two appropriate models, the effect of the time variation of the plasma frequency as well as the background magnetic field of the magnetoplasma medium are studied. Switching off the external magnetic field for the wave in the magnetoplasma medium converts a whistler wave to a wiggler magnetic field. Similar results are obtained with an intensification of the source wave as well as frequency upshift of the whistler wave for the collapsing plasma medium. By controlling the static magnetic field parameters and the level of ionization, the frequency shift ratio can be changed and the frequency transformer becomes tunable. The principle of frequency up-shifting using plasma permits the generation of signals from easily obtainable frequency bands and upshifts them into frequency bands not easily obtainable by other methods.

Comment on “Application of Kolmogorov entropy to the self-amplified spontaneous emission free-electron lasers” [Phys. Plasmas 11, 1663 (2004)

Zhang and Elgin [Phys. Plasmas 11, 1663 (2004)] studied the dynamical stability of electron trajectories in a free-electron laser (FEL). We have shown that their trajectories are not confined and diverge when self-fields are included or when the adiabatic wiggler magnetic field is removed. Therefore, their results are not relevant to FELs and to the experiment on which their study is based upon.

Effect of a wiggler magnetic field on the sum frequency generation in laser–plasma interactions

In this paper, we consider the process of sum frequency generation (SFG) in an underdense plasma in the presence of a wiggler magnetic field. It is shown that the presence of magnetic field leads to generate not only the even-order nonlinear phenomena such as transversal sum frequency waves but also longitudinal waves at fundamental and sum frequencies. It is also revealed that the wave vector k → 0 of wiggler magnetic field acts as a virtual photon of quantum energy zero and momentum ℏ k → 0 so that phase-matching condition is provided by the conservation of the momentum. Efficiency of the sum frequency generation is considered at different intensities, frequencies and number densities.

Stability of an electron beam in a two-frequency wiggler with a self-generated field

AbstractWe investigate the relativistic electron motions in a two-frequency wiggler magnetic field with self-generated fields. The equations of motion are derived from the Hamiltonian which include the self-generated field, and we find the steady-state orbit from the equations of motion. The stability of electron motion in a two-frequency wiggler is examined by the numerical simulation. We analyze the a dynamical systems using the fast Fourier transformation and the Poincarè surface of section to find the critical value which have the periodical electron motion and to optimize the two-frequency wiggler.

Chaotic Electron Motion in a Free-Electron Laser with a Two-Frequency Wiggler

In the high-power free-electron laser, we investigate the nonlinear beam dynamics of an electron in a two-frequency wiggler magnetic field to enhance the stability of the electron beam. The electron motion in a two-frequency wiggler is examined for the expanded Hamiltonian, and the equations of motion are derived from the Hamiltonian, which includes a two-frequency wiggler magnetic field. To optimize the two-frequency ratio parameter, we study the instability and chaotic phenomena of