导引场下电磁泵浦自由电子激光的非线性理论

本文以Vlasov-Maxwell方程组为基础,用非线性动力学理论研究了存在导引场情况下电磁波泵浦的自由电子激光器的作用机制,导出了线性及非线性色散关系式,求出了非线性不稳定性增长率和自由电子激光的能量转换效率.结果表明,只要合理地选择参量条件,附加导引场可以大大提高自由电子激光的增长率和能量转换效率.     

具有导向磁场的可变Wisggler自由电子激光器的物理机制

本文在忽略电子间相互作用的条件下,通过求解相对论洛伦兹方程,给出了在附加有导向磁场的可变Wiggler场中电子与电磁场相互作用的物理机制。同时讨论了几种通过改变导向磁场或Wiggler场参数的方法以提高能量转换速率的方法。     

具有导向磁场的可变Wiggler自由电子激光器的物理机制

本文在忽略电子间相互作用的条件下,通过求解相对论洛伦兹方程,给出了在附加有导向磁场的可变Wiggler场中电子与电磁场相互作用的物理机制。同时讨论了几种通过改变导向磁场或Wiggler场参数的方法以提高能量转换速率的方法。     

Chaotic electron trajectories in electromagnetic wiggler free-electron laser with a guide magnetic field

Summary The Hamiltonian for an electron travelling through a large-amplitude backward electromagnetic wave, an axial guide magnetic field and radiation field is formulated. Poincaré surface-of-section plots show that this Hamiltonian is non-integrable, and leads to chaotic trajectories. Equilibrium conditions are derived in the limit where the radiation field approaches zero. Compared to conventional FEL, the total energy of the system at pondermotive resonanceE _c is large, while the electron's critical energy γ_c is low for electromagnetic wiggler FEL. Moreover, the threshold wave amplitude (A _r=A _c) of beam chaoticity is found at lower values of the radiation field amplitude compared to magnetostatic wiggler FEL. Previous features confirmed that electromagnetic wiggler FEL can operate more coherently and more efficiently at moderated particle's energy compared to magnetostatic wiggler FEL.     

Growth rate enhancement of free-electron laser by two consecutive wigglers with axial magnetic field

The operative mechanism for a free-electron laser (FEL) with two consecutive helical wigglers having opposite circular polarization in the presence of an axial magnetic field is proposed and analysed. With the help of fluid theory, a tenth-degree polynomial dispersion equation for electromagnetic and space–charge waves is derived. The results are used to illustrate and discuss the dependence of growth rate on different system parameters. Finally, it is shown that for the same system parameters the growth rate of the proposed structure is more than the growth rate of instability in a conventional FEL.     

Three-dimensional motion of electrons in combined realistic helical wiggler with axial guide field for free-electron laser

3-D motion of electrons with on-axis and off-axis guiding centers in realistic helical wiggler and axial guide field is analysed. It is found that purely helical orbits couldnot exist for the electrons with off-axis guiding centers, except for those with on-axis guiding centers. Perturbation solutions of the electron's velocity and orbit averaged over the cyclotron angle are derived. Our calculations indicate the divergence of the electron orbits near resonance.     

Self-field effects on electron dynamics in a three-dimensional helical wiggler free-electron laser with axial magnetic field

An analytic linear theory of the electron dynamics in a three-dimensional helical wiggler free electron laser (FEL) with axial magnetic field is presented. Orbits are obtained by perturbing the steady state-trajectories in order to determine the characteristic frequencies Ω_± of the FEL. The effect of the self-fields on electron dynamics is studied and modified steady-state orbits and their stabilities have been analysed considering variation of electron energy and density. Among the features encountered is that in both group-I and group-II, one of the characteristic frequencies may have either signs affecting then the stability of the motion, while in group-II operation a repulsion of the frequencies at a pseudocrossing leads to highly perturbed trajectories when the wiggler frequency is approximately half the cyclotron frequency. Self-fields effects can significantly impair the stability of the electron orbits. For group-I orbits, they are more important for higher wiggler frequencies and lower beam energies. For group-II orbits, they remain less important for higher wiggler frequencies and lower beam energies before reaching the inversion zone, then they behave as for group-I orbits. It should be remarked that self-fields shift the inversion zone towards higher cyclotron frequencies the thing that is obtained by either decreasing the wiggler frequency or increasing the beam energy. It is shown that the axial velocity-induced self-magnetic field has a diamagnetic effect for both groups orbits, while the wiggler-induced self-magnetic field has a diamagnetic effect for group-I orbits and a paramagnetic effect for group-II orbits. The paramagnetic and diamagnetic effects are more important for higher beam energies and densities.     

Gain enhancement in two-stream free electron laser with a planar wiggler and an axial guide magnetic field

The theory for a two-stream free electron laser (FEL) consisting of a relativistic electron beam transported along the axis of a planar wiggler in the presence of an axial guiding magnetic field is proposed and investigated. The electron trajectories and the small signal gain are derived. The characteristic of the linear gain and the normalized maximum gain are studied numerically. The result shows that the normalized maximum gain is considerably enhanced in comparison with that of the single stream. The effect of the difference between the energies of the two beams in this configuration of FEL is also considered, and we find that the gain is affected by the energy differences between groups 1 and 2.     

A free-electron laser in a uniform magnetic field

The interaction of free electrons and free electromagnetic radiation, in the presence of a uniform magnetic field, can result in stimulated emission or absorption. We analyze the dynamics of single electrons by solving the classical, relativistic Lorentz force equations of motion in these combined fields. An electron may gain energy from, or lose energy to, the radiation field, depending crucially on the phase and oscillation frequency of the electron's helical motion within the superposed, circularly polarized light wave. To first order in the radiation field strength, electrons in a monoenergetic, uniformly distributed beam become spatially bunched, but there is no net energy change. To second order, however, the beam may experience a gain or loss of energy, corresponding to attenuation or amplification of radiation. We compare the bunching of this laser process to the bunching processes involved in 1) the Stanford free-electron laser and 2) the cyclotron maser, and find significant differences in each case. Our analytic results provide a clear, simple picture of the interaction process, and can be useful in exploring light amplification in astrophysical magnetic fields, the magnetosphere, or in laboratory devices. Supported in part by Army Contract No. DASG 60-77-C-0083 and NASA Grant NSG-7490.     

Gain enhancement in two-stream free electron laser with planar wiggler and axial guide magnetic field

The theory for the two-stream free electron laser (FEL) consisting of a relativistic electron beam transported along the axis of a planar wiggler in the presence of an axial guiding magnetic field is proposed and investigated. The electron trajectories and the small signal gain are derived. The characteristic of the linear gain and the normalized maximum gain are studied numerically. The result shows that the normalized maximum gain is considerably enhanced in comparison with that of the single stream. The effect of the difference between the energies of the two beams in this configuration of FEL is also considered, and we find that the gain is affected by the energy differences between groups 1 and 2.     

The effects of the guide field and tapered wiggler in free-electron laser

The interaction between electromagnetic field and electron beam was investigated numerically in a free-electron laser, using a new simulation code which consist of the three-dimensional electron motion, amplitude and phase of emitted radiation. The maintenance of the quality and stability of electron beam and the resonance condition through the wiggler is important to obtain the high gain and the high efficiency. But the electron orbits diverge and become unstable, and the resonance condition is not preserved because of the three-dimensional effects on the off-axis electron and the conversion of electron energy to electromagnetic field. To prevent those defects and improve the efficiency compared with the conventional case, we used the new methods such as the axial-guide field and tapered wiggler.     

Amplification and superradiant emission from a 33.3 GHz freeelectron 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     

Gyromonotron with an axial combining periodic magnetic field

On the base of the reference (1), making use of the linear kinetic theory, gyromonotron with an axial combining periodic magnetic field has been analysed in detail. The formulas of electron beam to wave interaction power, frequency shift and starting current, etc. have been derived.     

New critical current of ionization waves in an axial magnetic field

The upper critical current for the occurrence of ionization waves in an axial magnetic field is found in the positive column of rare-gas discharges. As the field is increased, the critical current slightly increases from the Pupp value, and after passing the maximum, finally becomes very small.     

Particle with anomalous moments in an axial magnetic field

The exact solutions of the generalized phenomenological Dirac equation in an axisymmetrical time-invariant magnetic field are discussed. The influence of an anomalous magnetic and a postulated electric moment on the spectrum of fermions moving in that field is investigated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 36–39, May, 1981.The author is grateful to Prof. V. G. Bagrov for interest and useful consultations.     

Analysis of the uniform magnetic field free-electron laser with scalarized photons in the microwave-spectral region

The recently developed concept of scalarized photons (formally photons of any polarization) is used to analyze the spontaneous and stimulated emission in the uniform magnetic field free-electron laser in the microwave spectral region. In fact, this free-electron laser is the simplest of many other, wiggler and wiggler-free free-electron lasers whose analyses could be done with scalarized photons in the small signal regime and whose physical parameters can be conveniently chosen for radiation to be generated in the microwave spectral region. As to the uniform magnetic field free-electron laser, which is treated here in some detail, with the electron beam energy of up to 10 MeV and the uniform magnetic field of up to 4 Tesla, the radiation (occurring with the fundamental and higher harmonic frequencies) can cover easily a 10 to 10,000 GHz spectral region.     

Theory of coupled mode oscillation in a laser with axial magnetic field

The nonlinear laser theory without noise is applied to calculate amplitudes, frequencies and beat frequencies of two circularly polarized modes in a laser with axial magnetic field. The resonator is allowed to have different damping constants for waves polarized inx- andy-direction. For small beat frequencies frequency locking occurs, and the modes combine to a linearly or elliptically polarized mode. The plane of polarization rotates with increasing magnetic field up to ± π/4.     

Quantum effects with an x-ray free-electron laser

A quantum kinetic equation coupled with Maxwell's equation is used to estimate the laser power required at an x-ray free-electron laser (XFEL) facility to expose intrinsically quantum effects in the process of QED vacuum decay via spontaneous pair production. A 9 -TW-peak XFEL laser with photon energy of 8.3 keV could be sufficient to initiate particle accumulation and the consequent formation of a plasma of spontaneously produced pairs. The evolution of the particle number in the plasma will exhibit non-Markovian aspects of the strong-field pair production process, and the plasma's internal currents will generate an electric field whose interference with that of the laser leads to plasma oscillations.