Helical Wiggler Field Research Articles

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.

Comparative study of inverse free-electron laser interaction based on helical and planar wiggler

In an inverse free-electron laser (IFEL) scheme, a comparative study of single electron acceleration is carried out using a tightly focused Gaussian laser beam along with helical and planar wiggler fields. The effect of laser and wiggler field parameters is analyzed on single-electron dynamics and its acceleration. For the laser field descriptions, up to fifth-order corrections are included in the diffraction angle to study the effect of a tight laser pulse on electron acceleration. The Lorentz equation is solved using the fourth-order Runge Kutta method. Our numerical results indicate that considerable electron energy is attained for the helical and planar wiggler both for the optimal laser and wiggler field parameters, respectively. The effect of the laser field, its waist -size, and the effect of the wiggler field and its tapering along undulator length is studied for both helical and planar wiggler. The total electron energy gain for the helical wiggler case is 1.3 GeV due to the long interaction length while for the planar wiggler case, the electron energy gain is limited to 300 MeV only due to its shorter interaction length. This comparative analysis will certainly help us to understand the electron dynamics in IFEL and show the importance of helical wiggler over planar wiggler.

Effects of Helical and Planar Wiggler Fields on the Dust Characteristics in a Plasma Sheath

Effects of Helical and Planar Wiggler Fields on the Dust Characteristics in a Plasma Sheath

Excitation modes in a cylindrical plasma waveguide with helical wiggler field and ion channel guiding

Analysis of high frequency eigen modes of a cylindrical metallic waveguide filled with a helical wiggler and a relativistic electron beam and guiding by an ion-channel is presented. A relativisticnonlinear wave equation is derived in a form including the coupling of EH, HE, HE betatron (HE - Be), and EH betatron (EH - Be) modes due to ion channel guiding and wiggler magnetic field. Six families of eigen modes are found. The cutoff frequencies in TM, TE modes are illustrated for this configuration.

Electron accelerators based on laser pulse propagation through plasma and in the presence of an obliquely external magnetic and a helical wiggler field

Electron accelerators based on laser pulse propagation through plasma and in the presence of an obliquely external magnetic and a helical wiggler field

Effect of two-stream instability on the saturation mechanism of a two-stream free-electron laser with a helical wiggler pump

In this paper we will investigate the effect of two-stream instability on saturation mechanism in Two-Stream Free Electron Laser (TSFEL) with a helical wiggler pump. A two-velocity relativistic electron beam propagates through the helical wiggler field. The relativistic electron stream is assumed to be cold. The slippage of the electromagnetic wave with respect to the electron beam is ignored. Self-consistent evolution of an electromagnetic wave in the presence of two-velocity electron beam is described by a set of coupled nonlinear differential equations in 1D approximation. Slowly varying envelope approximation is used and by the Runge–Kutta method algorithm is solved numerically. The power versus the axial distance has been plotted. It has been found that the TSFEL reaches the saturation regime in a shorter axial distance in comparison with the conventional FEL.

Electron trajectories and gain in free-electron lasers with three-dimensional helical wiggler and ion-channel guiding

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 Φ 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 γ 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 radiation forces in transverse components of the equation of motion included and results are compared with previous works in one-dimensional case.

The stability of electron orbits due to the wiggler field amplitude in free-electron laser

The relativistic electron orbits have been studied in the helical–wiggler field, which included self-field effect in free-electron laser. The equations of motion are derived from the Hamiltonian which includes self-field, and the steady-state orbit solutions were found from the equations of motion. We have analyzed the stability of electron orbits due to the wiggler field amplitude by numerical simulations. We have estimated the maximal Lyapunov exponents, which required estimation of the threshold value of the wiggler field amplitude for the onset of chaos in electron orbits.

Chaotic behaviour in a realizable helical-wiggler field

The motion of an individual electron for the case the wiggler magnetic field is described by a realizable helical wiggler is investigated. The dimensionless vector potential is considered to the leading-order vector potential for an ideal helical wiggler and the correction of the vector potential. Chaotic behaviour in a realizable helical wiggler field is examined for the expanded Hamiltonian in free-electron laser. We also analysed the focusing force provided by higher-order terms in the vector potential expansion, the effects of self-field, the particle trajectories and chaotic phenomena due to the wiggler field amplitude in a realizable helical wiggler by the numerical simulation.

Injection of electrons into the three-dimensional helical wiggler field in a free electron laser

Injection of electrons into a three-dimensional magnetostatic helical wiggler in the resonance region is studied numerically. Similarly to the one-dimensional situation, a considerable reduction in the amplitude of oscillations about the steady-state orbits is found when an axial magnetic field is changed adiabatically. On the other hand, interesting quasihelical trajectories are found for an annular beam in the resonance region. Therefore it seems the gain reduction in the magnetoresonance region can be overcome by this new injection method.

Excitation of EH mode in a free electron laser with a partially filled waveguide

A three-dimensional theory for a free electron laser with a positive or reversed axial-guide magnetic field in the collective regime is presented. A relativistic electron beam partially fills a cylindrical and metallic waveguide. A one-dimensional helical magnetic wiggler field, in the beam frame, decays into a forward-scattered space-charge wave and a backscattered EH waveguide mode. With relativistic mass correction in the beam frame a nonlinear wave equation is derived which describes the interaction between the wiggler field and the excited waves. Dispersion characteristics of the eigenmodes are studied. A formula for the lab-frame spatial growth rate of the parametrically excited waves is derived for a positive and reversed axial-guide magnetic field. The growth rate for the reversed axial-guide magnetic field was found to be around one order of magnitude smaller than for the positive field. Figures are presented to show the variation of the growth rate with axial-guide field and the ratio of the beam radius to the waveguide radius.

Polarization characteristics of spontaneous emission and off-axis coherent gain in a free-electron laser.

The polarization characteristics of spontaneous radiation from relativistic electrons moving through helical and planar wiggler fields are evaluated for imperfect beam injection. Maximum coherent gain in free-electron laser systems are seen to occur in optical fields having these polarization characteristics rather than those of the wiggler magnets. Coupling coefficients for an electron beam skewed at an angle to the optical mode are presented.

Excitation of a transverse magnetic waveguide mode near cutoff in a free-electron laser

A free-electron laser with a helical wiggler field, waveguide, and axial guide field operating in the collective regime infinitesimally above cutoff of a transverse magnetic (TM) mode is considered. The waveguide is completely filled with a relativistic electron beam. Beam-frame analysis of the parametric decay of the wiggler wave into a forward scattered space-charge wave and a backscattered TM mode is presented. A simple, analytical formula is derived for the laboratory-frame spatial growth rate. Calculations show that this stimulated Raman scattering process can occur if the axial guide field is sufficiently strong, and that the growth rate is enhanced when the beam-frame wiggler frequency is near the cyclotron frequency.

Axial free-electron laser interaction between an annular electron beam and an axisymmetric TM mode

Free-electron lasers (FEL's) operating with helical wiggler fields and axial guide fields are subject to orbit instability which causes additional particle loss as saturation is reached, A new type of FEL interaction possible between an annular electron beam and a TM/sub 0m/ mode is described here. This interaction is between the axial electron motion and an RF mode that is radially wiggled a in periodically rippled waveguide. The net transverse force integrated over a wiggle period on each of the particles in this type of device can be made to vanish by choosing the proper waveguide radius. The resulting particle orbits are more stable than those in conventional FEL's with helical wiggler fields. >

Observations of frequency chirping and phase of a free electron laser amplifier

We report observations of frequency chirping and phase of a free electron laser amplifier operating in the Raman regime. The FEL is driven by a mildly relativistic electron beam (750 kV, 25 ns) subjected to a combined axial magnetic field and a helical wiggler field. The input into the FEL amplifier is provided by a high power magnetron tuned to a frequency of 33.39 GHz. Phase and frequency shifts are measured both as a function of time and interaction length. It is found that in the Group I regime of FEL operation the output frequency is upshifted by ∼ 100 MHz, but smaller upshifts are observed in the Group II or the Reversed Field configurations.

High efficiency 33.3 GHz free electron laser amplifier with a reversed axial guide magnetic field

Abstract We report on a new regime of free electron laser operation using a helical wiggler field and a reversed axial guide magnetic field. The orientation of the axial field is such as to oppose the rotation of the electrons imparted by the helical field. The 33.3 GHz free electron laser amplifier is driven by a mildly relativistic electron beam (750 kV. 300 A. 30 ns) and generates 61 MW of radiation with a 27% conversion efficiency. The results are compared with those obtained when the axial guide field is in its conventional orientation where considerable loss of power and efficiency is observed.

Amplification and superradiant emission from a 33.3 GHz free electron laser with a reversed axial guide magnetic field

A new regime of free-electron laser (FEL) operation using a helical wiggler field and a reversed axial guide magnetic field is reported. The orientation of the axial field is such as to oppose the electron rotation imparted by the helical field. The 33.3-GHz FEL amplifier is driven by a mildly relativistic electron beam (750 kV 300 A, 30 ns) and generates 61 MW of radiation with a 27% conversion efficiency. The results are compared with those obtained when the axial guide field is in its conventional orientation, where considerable loss of power and efficiency is observed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Experimental study of a 33.3-GHz free-electron-laser amplifier with a reversed axial guide magnetic field.

We report on a new regime of free-electron-laser operation with reversed axial guide magnetic field, in which the rotational motion of the electrons in the helical wiggler field is opposed by the presence of the uniform guide field. The 33.3-GHz free-electron-laser amplifier is driven by a mildly relativistic electron beam (750 kV, 300 A, 30 ns) and generates 61 MW of radiation with a 27% conversion efficiency. Measurements with the conventional orientation of the axial field show a considerable loss of power and efficiency.

Chaotic particle dynamics in free-electron lasers

The motion of a relativistic test electron in a free-electron laser can be altered significantly by the equilibrium self-field effects produced by the beam space charge and current and by the transverse spatial inhomogeneities in a realizable magnetic wiggler field. In a field configuration consisting of an ideal (constant-amplitude) helical-wiggler field and a uniform axial-guide field, it is shown in a model that the inclusion of self-field effects destroys the integrability of the particle equations of motion. Consequently, the group-I orbits and the group-II orbits become chaotic at sufficiently high beam density. An analytical estimate of the threshold value of the self-field parameter ${\mathrm{\ensuremath{\epsilon}}}_{\mathit{s}}$=${\mathrm{\ensuremath{\omega}}}_{\mathit{p}\mathit{b}}^{2}$/${\mathit{c}}^{2}$${\mathit{k}}_{\mathit{w}}^{2}$ for the onset of chaos is obtained and found to be in good agreement with computer simulations. In addition, the effects of transverse spatial gradients in a realizable helical-wiggler field with three-dimensional spatial variations are investigated in the absence of an axial-guide field, but including self-field effects. For a thin electron beam (${\mathit{k}}_{\mathit{w}}^{2}$${\mathit{r}}_{\mathit{b}}^{2}$\ensuremath{\ll}1) and small wiggler field amplitude (${\mathit{a}}_{\mathit{w}}^{2}$\ensuremath{\ll}${\ensuremath{\gamma}}_{\mathit{b}}^{2}$), it is shown that the motion is regular and confined radially provided ${\mathrm{\ensuremath{\epsilon}}}_{\mathit{a}}$${\ensuremath{\gamma}}_{\mathit{b}}$${\mathit{a}}_{\mathit{w}}^{2}$/(1+${\mathit{a}}_{\mathit{w}}^{2}$). However, because of the intrinsic nonintegrability of the motion, the regular region in phase space diminishes in size as the wiggler amplitude is increased. The threshold value of the wiggler amplitude for the onset of chaos is estimated analytically and confirmed by computer simulations for the special case where self-field effects are negligibly small. Moreover, it is shown that the particle motion becomes chaotic on a time scale comparable with the beam transit time through a few wiggler periods.

ELECTRON TRAJECTORIES AND STABILITY IN FEL WITH AN AXIAL GUIDE MAGNETIC FIELD

The single-particle trajectories of relativistic electrons are studied in a magnetic field con-figuration consisting of a uniform axial guide field and a helical periodic wiggler field. The steady-state trajectories and the first order perturbed trajectories are analysed carefully. Based on the numerical simulations about the experiments which have been made at Shanghai Institute of Optics and Fine Mechanics, the effect of the betatron oscillations due to the transverse varing of wiggler field is first shown in the case that there is a axial guide field. In this case the betatron oscillations equations are drived. Its period and the relation between phase in X dirction and in Y dirction are obtioned. Further more, numerical simulations are made. The results of analytical calculation are in good agreement with the numerical simulations.