Investigation of the gain regimes and gain parameters of the free electron laser dispersion equation

We compute the small signal gain curve and various gain parameters by solving numerically the generalized gain-dispersion equation of free electron lasers (FEL), which characterizes the conventional magnetic bremsstrahlung FEL, as well as a large number of other FEL devices. The model includes high gain, collective, and axial velocity spread effects, and some waveguide effects. The FEL gain regimes are investigated and presented in terms of only three universal FEL characteristic parameters. The approximative analytic gain expressions are compared to the numerical computation results, and the approximation error is computed and displayed. In the intermediate regimes (high-low gain, tenuous-collective beam, cold-warm beam), the gain parameters are given in terms of useful curves, and a heuristic approximative formula is suggested for estimating the axial velocity spread gain reduction factor in all gain regimes. We also define and compute gain bandwidth and beam quality acceptance parameters in all gain regimes.     

Effect of velocity spread on finite-length free electron laser gain

A theory of general stimulated backscattering by a hot, relativistic electron beam propagating through a spatially periodic, transverse magnetostatic field is presented. The electrons are chosen to have a Lorentzian distribution in velocity space. Though energy spread acts to diminish gain, its effect is negligible if Δγ/γ < < N_-1, where N is the number of undulator periods. The analysis is linear and applicable to both the single-particle and collective regimes.     

An optimized multicomponent wiggler design for a free electron laser oscillator

An optimized multicomponent wiggler configuration for a high-power free electron laser (FEL) oscillator is presented which utilizes the TRW planar wiggler and the electron beam from the Stanford superconducting accelerator. The analysis shows that the design avoids the possibility of multimode competition at low power and eliminates the frequency chirp during the power build-up in the cavity. The small-signal gain is large enough that the device is expected to start from the noise level. The optimization of the design is confirmed by the numerical observation of its characteristics dependence on individual physical parameters.     

A prebunched free electron laser

The narrow width of an rf-accelerated electron micropulse can be exploited to yield gain significantly higher than in the conventional FEL. If the micropulses are much shorter than the wavelength of the generated wave and the electrons are resonant with the FEL beat wave, then a low order prebunched FEL interaction results. All electrons lose energy to the wave     

一种由强光担任摇摆器的新型自由电子激光器及其增益分析

提出了一种由超短脉冲双光束担任摇摆器的自由电子激光器的原理及设计方案,并在单电子近似的基础上给出了计算其增益的联立方程组,以用于数值模拟.指出了实现一种紧凑、廉价的可调谐光源的可能性.     

Degradation in gain for a free electron laser amplifier due to electron momentum spread

A finite spread in axial momentum for the electron beam in a free electron laser amplifier is shown to decrease the small-signal gain. For millimeter and sub-millimeter wave amplifiers, where exponential growth dominates the gain, it is shown that the gain is approximately 3 db below that for a cold beam if the relative momentum spread (Δu/u)_1/2 = (G_o/248)^1/2 (λ_o/L), where G_o?1 is the gain in db for the cold-beam case, λ_o is the magnetic wiggler period, and L is the amplifier length. Exact numerical examples are given for representative FEL amplifiers at 35 and 550 GHz.     

The study on the gain expression in the single-particle theory of free electron laser

Nonlinear pendulum equation is the fundamental one of the single particle theory in the free electron lasers (FELS). From its solution the gain expression can be derived. In this paper, an exact solution of it has been obtained for the first time, and similar result is also obtained as in the approximation of weak field by Colson.     

集体区自由电子激光器增益特性的研究

工作在超辐射模式下的集体区自由电子激光器的增益特性研究可以通过改变互作用区长度及泵浦强度来进行。我们利用偏转磁场可以获得任意的相互作用区长度。实验结果证明,工作在集体区的自由电子激光的辐射增益随泵浦磁场近似呈1.7次方关系,实验测得的增益系数范围为0.4dB/cm到1.38dB/cm。     

A compact free electron laser investigation

An electron beam source based on pseudospark discharge was successful in operation at the beam voltage of 200keV and beam current of 2kA. The detailed design of a compact free electron laser using an electron beam by a pseudospark discharge is described. The compact free electron laser consists of a smaller Marx generator with 6 capacitors and switches, a water capacitance of 6nF and a beam source with a high brightness of 3×10¹¹ A/(m rad)². The computer simulation shows that an output power of 101MW is expected at a frequency of 38GHz with a beam energy of 300keV, a current of 2kA and a beam emittance of 48mm mraa.     

A novel Smith-Purcell free electron laser

An experiment on a novel Smith–Purcell free electron laser (FEL) is described in this paper. The FEL is driven by a relativistic sheet electron beam of middle energy. The high frequency system of the device is a quasi-optical resonator composed of a diffraction grating and a three-mirror reflector. Coherent radiation with a peak power of tens of kW at the 3 mm waveband is sucessfully detected from an experimental facility. The main experimental parameters are: sheet beam energy from 400 kV to 500 kV; pulse length of voltage 70 ns; pulse beam current 0.2 kA; synchronous guide magnetic field up to 1.2 T with 10 ms pulse length; and grating period 2.2 mm.     

Three dimensional gain analysis of free electron laser with focusing permanent magnet wiggler

A three dimensional simulation software system developed to estimate a free electron laser (FEL) gain has been applied to FEL using a standard plane polarized wiggler and an alternately shifted magnet wiggler. It is seen for the latter wiggler that a large filling factor could be selected and each maximum gain corresponding to each orbit of electron beam concentrates at a certain frequency region of FEL radiation. It is, therefore, implied that a proper shift between the adjacent magnets in the wiggler produces the improvement of the FEL gain.     

Regenerative gain in a Raman free-electron laser oscillator

A parametric study of gain in a millimeter-wave Raman free-electron laser oscillator and comparisons to linear theory are carried out. The intense (1 kA/cm²), relativistic (600-800 keV), cold [(deltagamma/gamma)_{parallel} < 1percent] electron beam employed is guided by a 9.45 kG magnetic field through a 1.45 cm period, 49.5 cm long uniform undulator. Operation at < 1 kG pump field results in a < 10 percent electron quiver velocity (upsilon_{perp}/upsilon_{parallel}) velocity. The laser power output has been mea sured at ∼ 3 MW corresponding to an efficiency of 4 percent, and tunability in the 90-170 GHz range has been achieved with a narrow linewidth (Delta lambda/lambda leq 1percent). Using a new technique, linear small-signal growth rates have been unfolded from the oscillator startup delays. Excellent agreement is found with three-dimensional small-signal calculations for both the spatial growth rate and the resonance frequency. One-dimensional theory was found to predict shorter wavelength laser output than that observed.     

On the gain of the free electron laser (FEL) amplifier for a nonmonoenergetic beam

An accurate analysis of the gain and the electron beam evolution in a free electron laser (FEL) amplifier in terms of the laser field intensity and of the initial momentum distribution of the electron beam is carried out using the exact solution of the beam evolution equation. The effect of the energy spread both in the small-signal and in the saturation regime is investigated.     

Hamiltonian model of a free electron laser including high-density effects

Both the Compton and the Raman regimes of a free electron laser are described by a relativistic Hamiltonian which originates the evolution equations for 2N+2 canonically conjugate electron and field variables, with the space coordinate as the independent variable. Space charge and field contribution to electron transverse velocity are included.     

自由电子激光器中电子相互作用对增益的影响

求出了螺旋磁场泵自由电子激光器中含电子相互作用的增益表达式,并进行了讨论。     

微型自由电子激光——电扭摆器

本文利用铁电晶体自发极化产生的强大周期性表面势,首次提出新的自由电子激光原理.据此原理,可以设计小型、廉价、高效率、高频率自由电子激光器,它在技术上是可能实现的.     

Betatron-synchrotron resonance in free electron laser

In terms of Bogoliubov's nonlinear theory, the first five betatron-synchrotron resonances of Ω_s=(p q)2K_β, p/q=1/2, 1, 3/2, 1/3, 2/3 which may occur during laser satulation establishing process have been generally examined. Contrast to previous studies we found that the most dangerous resonance does not take place in the vicinity of Ω_s=2k_β, but in that of Ω_s=k_β. The width of region of Ω_s=k_β is proportional to ε with ε∞ (k _w ² /kβ) remittance, the passing ‘time’ over the region due to the laser field being amplified is only one pass over the undulator at most and depends on the gain, and the increment of synchrotron amplitude in passing time is proportional to ε. In summary we conclude that the betatron-synchrotron resonances do not have any significant effect for detrapping off-axis electrons in a practical case.     

星战自由电子激光器赛马

经过几年的竞赛,地基自由电子激光技术组合实验的激光器子系统投标已结束.本文评述了感应型自由电子激光器和射频型自由电子激光器的性能和取得的重大进展,并介绍了了高功率激光的大气补偿和束传播研究的最新结果.     

The Beijing free electron laser project

The Beijing Free Electron Laser Project (BFELP) is a Compton Regime, FEL facility working in the infra-red region in the first phase, being constructed at the Institute of High Energy Physics (IHEP), Academia Sinica, using the beam from a 30 MeV rf linac as the electron source. In this paper, the goals and design principles of this project are first discussed. Then some one-dimensional simulation results, supplemented by analytical modification, are presented which lay the basis for the choice of the main physical parameters of the system. The general layout of the facility is given and the main requirements of the sub-systems indicated