Quantum theory of a free electron in a tapered wiggler field

It is pointed out that a slight modification of the relativistic quantum theory of a free electron in a uniform wiggler field enables the study of motion in a tapered wiggler field of the form $\text{k}{}_{\mathrm{w}}{}^1\text{= k}{}_{\mathrm{w}}\text{?}\text{b}\text{z}$ which merits attention. The lower limit of z is 800 cm. The exact relativistic quantum mechanical calculation shows an enhancement in the gain for single pass. The frequencies are up-shifted by amounts depending on the parameter b.     

自由电子激光摇摆器磁测系统

根据理论分析及实际加工水平,设计了一套摇摆器磁场测量系统,同时对影响磁测系统整体性能的主要参数进行了详尽分析。摇摆器磁测装置主要由气浮运动平台、测磁设备及控制系统组成,其主要功能是对霍尔探头的位置与磁场数据进行高精度测量及同步采集。主要参数如下:z向定位精度小于5μm,重复定位精度小于2μm;霍尔探头的测量精度为0.05%,重复测量精度为0.01%,响应频率为1kHz;数据采集卡的采样率不小于1000。     

自由电子激光摇摆器磁测系统

根据理论分析及实际加工水平,设计了一套摇摆器磁场测量系统,同时对影响磁测系统整体性能的主要参数进行了详尽分析。摇摆器磁测装置主要由气浮运动平台、测磁设备及控制系统组成,其主要功能是对霍尔探头的位置与磁场数据进行高精度测量及同步采集。主要参数如下: z向定位精度小于5 m,重复定位精度小于2 m;霍尔探头的测量精度为0.05%,重复测量精度为0.01%,响应频率为1 kHz;数据采集卡的采样率不小于1000。     

Compact free electron lasers: From Cerenkov to waveguide free electron lasers

The basic principles of free electron generators of coherent radiation and the practical considerations related to the development of far infrared and sub-millimeter wave sources are discussed in this paper. The attention is focused on compact devices, which reduce the size and cost issue. A review of the main results obtained at the Frascati FEL Facility is presented together with the planned experiments.     

Planar electron beams in a wiggler magnet array

Transport of high current (～kA range with particle energy ～1 MeV) planar electron beams is a topic of increasing interest for applications in high-power (1–10 GW) and high-frequency (10–20 GHz) microwave devices such as backward wave oscillator (BWO), klystrons, gyro-BWOs, etc. In this paper, we give a simulated result for transport of electron beams with velocity $V_{\rm b} = 5.23 \times 10^{8}$  cm s^???1, relativistic factor γ?=?1.16, and beam voltage = ～80 kV in notched wiggler magnet array. The calculation includes self-consistent effects of beam-generated fields. Our results show that the notched wiggler configuration with ～6.97 kG magnetic field strength can provide vertical and horizontal confinements for a sheet electron beam with 0.3 cm thickness and 2 cm width. The feasibility calculation addresses to a system expected to drive for 13–20 GHz BWO with rippled waveguide parameters as width w?=?3.0 cm, thickness t?=?1.0 cm, corrugation depth h?=?0.225 cm, and spatial periodicity d?=?1.67 cm.     

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.     

Radiation amplification in free electron lasers with a synchronizing magnetic field

Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 10, pp. 1238–1249, October, 1989.     

Wave profile modification in the free electron laser with andwithout a waveguide

The modification of the transverse wave profile by the free electron laser (FEL) interaction in the collective Raman regime is considered. The gain is calculated and the transverse wave profile is found by solving for the eigenvalues and the actual eigenmodes of the system. When a waveguide is employed, a strong FEL interaction is shown to couple various vacuum waveguide modes, as was demonstrated by A. Bhattacharjee et al. (1988). When no waveguide or cavity is present, a coupling parameter which measures the strength of the interaction is identified. Expressions are derived for the gain for large and small values of the coupling parameter, corresponding to a strong optical guiding and large diffraction, respectively. Comparing the present results for the Raman regime with previous results for the strong pump regime, it is shown that the gain scales differently in each case, depending on both the regime of operation and on the beam geometry. The linear analysis is valid when the signal is small, and is useful mainly when the gain is high prior to saturation     

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.     

Electron orbit in a combined plasma wave wiggler and an axial guidemagnetic field free electron laser near magnetoresonance

The nonlinear electron orbit dynamics is presented for a combined electrostatic plasma wave wiggler and an axial guide magnetic field free electron laser near magnetoresonance. The perpendicular orbit equation is derived and simplified identical to the wave-driven nonlinear oscillator equation but with different expressions of parameters. The nonlinear effect induced by the inclusion of β_⊥² in the relativistic factor γ is dominant in governing the perpendicular wiggling velocity and the orbit excursion even in the case of β_⊥²≪β_∥² , where γ=(1-β₁²-β_∥ ²)^-1/2. The dependence of the maximum perpendicular wiggling velocity and the orbit excursion on the wiggler constant, the wiggler frequency, and the initial parameters of motion is given analytically     

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.     

Efficient weak-light amplification through phase control in a quantum well waveguide with electron spin coherence

We propose and analyze a new scheme to realize efficient weak-light amplification via phase control in a GaAs quantum well (QW) waveguide when driven coherently by two orthogonally polarized optical fields (a σ-polarized probe field and a π-polarized control field). It is shown that the amplification and absorption properties of the system are very sensitive to the relative phase between these driving fields. By choosing the relative phase appropriately, the enhanced amplification of the weak σ-polarized radiated field can be achieved in such a QW waveguide. We support our results by numerical calculation and analytical explanation. These theoretical investigations may find applications in devising the QW waveguide amplifier at room temperature.     

Backward Raman amplification in a plasma waveguide

Backward Raman amplification of a short laser pulse in a plasma waveguide is demonstrated. With a guided seed pulse of 0.8-microJ energy and a pump pulse of 345-mJ energy in a 9-mm-long optically preformed plasma waveguide, 910-fold energy amplification is achieved. Heating of the plasma by the long pump pulse is identified to be a key issue for plasma-waveguide-based backward Raman amplifiers.     

Microwave system for free electron masers based on a curved open waveguide

A new microwave system for free electron masers of millimeter and submillimeter wavelength ranges on the basis of an open quasi-optical waveguide in the form of two slightly deformed metallic planes is discussed. The system gives the possibility to control the wavebeam trajectory and, in particular, to separate wave and electron beams.Some basic solutions and results of demonstration experiment are presented.     

The effects of self-fields on the electron trajectory in a two-stream free electron laser with a helical wiggler and an axial guiding magnetic field

A theory for the two-stream free-electron laser(TSFEL) with a helical wiggler and an axial guide magnetic field is developed.In the analysis,the effects of self-fields are taken into account.An analysis of the two-stream steady-state electron trajectories is given by solving the equation of motion.Numerical calculations show that there are seven groups of orbits in the presence of self-fields instead of two groups reported in the absence of self-fields.The stability of the trajectories is studied numerically.     

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.     

Nonlinear analysis of wiggler taper, node competition, andspace-charge effects for a 280-GHz free electron laser

The nonlinear characteristics of a 280-GHz free electron laser (FEL) are simulated by numerical computation. The three-dimensional set of coupled nonlinear differential equations is solved for a set of TE and TM modes valid for the high gain Compton regime. The use of a nonlinear taper for efficiency enhancement, the sensitivity of gain to competing mode power levels, space-charge effects, and the effect of electron beam source distributions on gain and efficiency are examined for a 10-MeV, 3-kA beam. It is found that the nonlinear taper greatly enhances the gain and efficiency and makes the saturation power levels relatively insensitive to the competing mode power levels. The efficiency is increased to 48% by means of a nonlinear taper in which the 3-D and wiggler-averaged codes are compared and the effects of space charge are found to reduce the efficiency to a level of 32%. The effect of beam quality in terms of the four volume phase space is examined and found to have an observable effect at this wavelength     

用于自由电子激光的S波段J型波导馈电加速管

随着波导式耦合行波加速管设计梯度的日益提高,为了防止加速管输入耦合器电场的横向动量在束流通过加速器耦合器时引起束流品质的下降,侧壁开有两个对称耦合孔的对称双馈圆柱腔获得了广泛的应用。研制的S波段J型波导馈电加速管即为双馈圆柱腔中的一种,研制样管在老练平台上老练时的最高加速梯度达到30 MV/m。然而因为四极场的存在,开有两个耦合孔的圆柱耦合腔内,仍然会引起轴向电场的幅度和相位在横向的梯度,从而使束流发射度变差。在理论上对J型波导馈电的跑道式耦合腔进行了研究,通过与圆柱腔进行比对模拟计算,证明跑道式耦合器可以很好地改善轴向电场在横向平面内非近轴区域沿圆周的场强一致性,从而减小四极场的影响。重要的是,J型波导馈电跑道式耦合腔的机械加工、测试比圆柱腔更加容易实现,是未来双馈加速器发展的一个理想方向。     

用于自由电子激光的S波段J型波导馈电加速管

随着波导式耦合行波加速管设计梯度的日益提高,为了防止加速管输入耦合器电场的横向动量在束流通过加速器耦合器时引起束流品质的下降,侧壁开有两个对称耦合孔的对称双馈圆柱腔获得了广泛的应用。研制的S波段J型波导馈电加速管即为双馈圆柱腔中的一种,研制样管在老练平台上老练时的最高加速梯度达到30 MV/m。然而因为四极场的存在,开有两个耦合孔的圆柱耦合腔内,仍然会引起轴向电场的幅度和相位在横向的梯度,从而使束流发射度变差。在理论上对J型波导馈电的跑道式耦合腔进行了研究,通过与圆柱腔进行比对模拟计算,证明跑道式耦合器可以很好地改善轴向电场在横向平面内非近轴区域沿圆周的场强一致性,从而减小四极场的影响。重要的是,J型波导馈电跑道式耦合腔的机械加工、测试比圆柱腔更加容易实现,是未来双馈加速器发展的一个理想方向。     

Effect of betatron oscillations on waveguide free electron laser gain

In this paper we analyse the spontaneous emission and gain spectrum of a waveguide free electron laser with betatron motion included in the analysis. The zero slippage condition and the small signal gain in the waveguide free electron laser is discussed.