Axial-guide Magnetic Field Research Articles

Quantum regime of a plasma-wave-pumped free-electron laser in the presence of an axial magnetic field

The quantum regime of a plasma-whistler-wave-pumped free-electron laser (FEL) in the presence of an axial-guide magnetic field is presented. By quantizing both the plasma whistler field and axial magnetic field, an N-particle three-dimensional Hamiltonian of quantum-FEL (QFEL) has been derived. Employing Heisenberg evolution equations and introducing a new collective operator which controls the vertical motion of electrons, a quantum dispersion relation of the plasma whistler wiggler has been obtained analytically. Numerical results indicate that, by increasing the intrinsic quantum momentum spread and/or increasing the axial magnetic field strength, the bunching and the radiation fields grow exponentially. In addition, a spiking behavior of the spectrum was observed with increasing cyclotron frequency which provides an enormous improvement in the coherence of QFEL radiation even in a limit close-to-classical regime, where an overlapping of these spikes is observed. Also, an upper limit of the intrinsic quantum momentum spread which depends on the value of the cyclotron frequency was found.

Stability analysis for electron orbits in a harmonic wiggler

A high-power free-electron laser is operated at a high electron beam current and high wiggler magnetic field, and the stability of the electron motion under those conditions is important for obtaining sufficiently large gain and high efficiency. In this study, a harmonic wiggler was used to improve the stability of the electron beam. Guiding-center variables were applied to analyze the complex electron motion in the electric and magnetic fields in combination with the wiggler magnetic field, the axial-guide magnetic field, and the self-generated field. The steady-state orbits of an electron in the harmonic wiggler were calculated analytically, and the Poincar+AOg surface of section plot was generated to distinguish between regular and chaotic behavior in the electron orbits. Finally, when the harmonic wiggler was used, the electron orbits were found to become stable compared with those in the conventional wiggler.

Controlling chaotic behavior of the equilibrium electrons by simultaneous using of two guiding fields in a free-electron laser with an electromagnetic-wave wiggler

In the present paper the effects of the combination of the axial-guide magnetic field and the ion-channel guiding on the chaotic trajectories in a free-electron laser with electromagnetic-wave wiggler have been considered. It is shown that the simultaneous using of the two guiding fields in the certain conditions causes chaotic behavior in the electron motion. It is also illustrated that the chaotic trajectories decrease as the ion-channel density or the strength of the axial magnetic field increases. The transition from the chaotic trajectories to regular trajectories, occurs at a special ion-channel density, ω−it, or a particular amount of the strength of the axial magnetic field, at. Furthermore numerically calculation shows that the normalized ion-channel frequency of the transition, ω−it, reduces by increasing the axial magnetic field. Also ω−i increase causes the trajectories to be regular at the weaker at. The electron motion has been altered significantly by the self-fields effects. It is demonstrated that, the self-fields cause a decrement in the chaotic trajectories. This is in contrast to the idealized helical wiggler FEL with the axial magnetic field guiding.

The effects of self-fields on the electron trajectory and gain in a two-stream electromagnetically pumped free-electron laser with axial guiding field

A theory of a two-stream free-electron laser in a combined electromagnetic wiggler (EMW) is developed, in which we use an axial-guide magnetic field and take into account the effects of the self-fields. The electron trajectories and the small signal gain are derived. The stability of the trajectories, the characteristics of the linear-gain, and the normalised maximum gain are studied numerically. The results show that there are nine stable groups of orbits in the presence of self-fields instead of seven groups reported in the absence of the self-field. It is also shown that the normalised gains of four groups of the orbits are decreasing and those for the rest of them are increasing with growing . Furthermore, it is found that the two-stream laser with self-field enhances the maximum gain in comparison with the single stream case.

Electrostatic beam modes in a free-electron laser with a coaxial wiggler

An analysis of the propagation of an electrostatic beam space-charge wave through a coaxial wiggler magnetic field and an axial-guide magnetic field is presented. Equations for the electron orbital velocity, rate of change of axial velocity with Lorentz factor, and the dispersion relation are derived. The effects of the combined wiggler and axial-guide fields on the rate of change of the axial velocity with electron energy and on the effective electron density in the dispersion relation are studied numerically. The present theory predicts that electrostatic negative mass instabilities do not exist in a coaxial wiggler.

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.

Unified nonlinear orbit dynamics of an equilibrium electron in a helical wiggler with a positive or reversed axial-guide magnetic field at magnetoresonance.

Nonlinear orbit dynamics are investigated analytically for a single relativistic electron in an ideal helical wiggler with a positive or reversed axial-guide magnetic field at magnetoresonance. An algebraic equation is derived for determining the maximum perpendicular velocity. The upper limit for a transverse electron orbit excursion is found to be proportional to ${\mathrm{\ensuremath{\varepsilon}}}^{1/3}$ and \ensuremath{\varepsilon} for the positive and reversed guide field, respectively, where \ensuremath{\varepsilon} is the ratio of the wiggler field to the guide field. The analytical results are in agreement with numerical calculations.

The effects of space charge and axial-guide magnetic fields on the gain in an electromagnetically pumped free-electron laser

Under the resonance condition, the effects of space charge and axial-guide magnetic fields are discussed in an electromagnetically pumped free-electron laser. An expression for the small-signal gain, including the space charge effects, is obtained. The stability conditions for both the space charge field and the electron trajectories are investigated in the presence of the radiation field. It is shown that the axial-guide magnetic field has a bounded amplifying effect on the gain.

The equilibrium analysis of the differential difference equation for the probability amplitude in a wiggler-pumped free-electron laser with an axial-guide magnetic field

In the Bambini-Renieri frame, the equilibrium equation of motion for the probability amplitude is given for a wiggler-pumped free-electron laser with an axial-guide magnetic field. The solution for this differential difference equation is obtained using the Lie algebraic method in the small electron-recoil and weak-coupling limits. The spontaneous emission is calculated and the effect of the electron cyclotron motion is discussed.

THE CONTROLLING PARAMETER IN A WIGGLER-PUMPED FREE-ELECTRON LASER WITH AN AXIAL-GUIDE MAGNETIC FIELD

The basic equations are given for a wiggler-pumped free-electron laser with an axial-guide magnetic field. It is found that the evolution of the electron-field system is determined by a controlling parameter which contains the contributions of the electron beam, wiggler field, axial-guide magnetic field, and the initial state of the system. The collective instability is discussed and the threshold value of the controfling parameter is obtained. Farthermore, the radiation field is expressed in the cases of W＜WT and W＞WT.

Intrinsic linewidth of a free-electron laser with an axial-guide magnetic field.

The intrinsic linewidth of a free-electron laser with an axial-guide magnetic field is analyzed using a master Fokker-Planck equation. All electron emissions caused by the axial bremsstrahlung and the transverse cyclotron have contributions to the linewidth.

How to obtain the quantum state of a free-electron laser with an axial-guide magnetic field from its classical trajectories

A procedure is given to obtain the quantum state of a free-electron laser with an axial-guide field from a coherent state. It is shown that the coherent state corresponds to the classical trajectories. The small-signal gain is obtained and the effects of the guide field on the gain are bounded in order to keep the orbital and electrostatic stabilities.

Space-charge and axial-field effects in a free-electron laser with an axial-guide magnetic field

Space-charge and axial-field effects are discussed for a free-electron laser with an axial-guide magnetic field. It is found that the maximum gain increases with the beam density and gain saturation occurs for high beam density. The laser frequency is upshifted and downshifted in the low and high density cases respectively. The regimes which permit the amplifying effect of the guide field and the stabilities of both the electron trajectories and the electrostatic mode are found. The maximum amplifying coefficient of the guide field is also obtained by using the stability conditions.

Photon statistics in a free-electron laser with an axial-guide magnetic field.

Starting from an initial state with an electron energy ${\mathit{p}}_{0}^{2}$/2m+\ensuremath{\Elzxh}${\mathrm{\ensuremath{\omega}}}_{\mathit{c}}$/2, a vacuum-laser field, and a coherent wiggler field, I discuss photon statistics in a free-electron laser with an axial-guide magnetic field. It is found that the axial field can weaken the squeezing, enhance the positive (for \ensuremath{\theta}>0) and negative (for \ensuremath{\theta}0) gain, and strengthen the bunching (for \ensuremath{\theta}>0) and antibunching (for \ensuremath{\theta}0).

Cold-Fluid Analysis of the Space-Charge Effects in an Electromagnetically Pumped Free-Electron Laser with an Axial-Guide Magnetic Field

The space-charge effects are analysed and five kinds of fluid waves are obtained in the e-beam density and the axial-current density for an electromagnetically pumped free-electron laser with an axial-guide magnetic field by using the cold-fluid theory. To enhance the gain, the guide field must be in this regime: , where and is the frequency (wave number) of the wiggler.

Higher Harmonic in Free Electron Laser with Combined Electromagnetic Wiggler and Axial Guide Magnetic Fields

Following a single-particle approach, a detailed analysis of the higher harmonic in free electron laser (FEL) with combined electromagnetic wiggler and axial guide magnetic fields is derived. The spontaneous emission spectrum and the gain in the low-gain Compton regime are also calculated in detail. This analysis results in a clear resonance condition and shows that this kind of FEL can generate significant coherent harmonic emission of radiation with axial guide magnetic field of suitable strength.

Influence of Beam Equilibrium Self-fields on Linear Gain for a Free Electron Laser

The small-signal linear gain for a combined electromagnetic wiggler and an axial-guide magnetic field free electron laser is derived within the presence of beam equilibrium self-fields. The numerical results show that the gain is reduced as the self-fields increase.

The effects of an axial-guide magnetic field in an electromagnetically pumped free-electron laser

The analytical expression of the small-signal gain, including the space-charge effects, is obtained for an electromagnetically pumped free-electron laser with an axial-guide magnetic field by using the cold-fluid theory. An amplifying coefficient is introduced to describe the effects of the axial-guide magnetic field for conventional experiments. >

Linear gain of a free-electron laser with an electromagnetic wiggler and an axial-guide magnetic field.

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 ${\ensuremath{\Omega}}_{0}$\ensuremath{\simeq}${\ensuremath{\gamma}}_{0}$(${\ensuremath{\omega}}_{w}$+${k}_{w}$${v}_{?}$), where ${\ensuremath{\Omega}}_{0}$ is the axial gyrofrequency, ${\ensuremath{\gamma}}_{0}$ is the relativistic factor for the electron beam, ${v}_{?}$ is the axial velocity of the electron beam, and (${\ensuremath{\omega}}_{w}$,${k}_{w}$) are the frequency and wave vector of the electromagnetic wiggler.