有矩形波导和线性摆动器的自由电子激光器的特性研究

本文研究圆柱电子束通过矩形波导和线性摆动器时产生相干辐射的特性。用线性化弗拉索夫-麦克斯韦方程分析了因对自洽的电子束平衡态引起扰动产生的不稳定性。导出了TMmn模的色散方程并数值计算了辐射频率和增长率与电子束能量、轴向磁场、摆动器强度和波长以及电子束半径的关系。     

Comparison of dc electric field and tapered wiggler free electron laser efficiency enhancement schemes

A constant parameter wiggler free electron laser using a dc electric field for efficiency enhancement is compared to several tapered wiggler efficiency enhancement schemes. Analytical expressions for the efficiency in the plane wave, infinitesimally small radius electron beam limit are derived and compared. Numerical simulations for a Gaussian radiation field and finite radius electron beam with an output radiation wavelength of 2 μm are presented. For finite radius electron beams, the extraction efficiency using a dc electric field is somewhat greater than or equal to that using proposed tapering schemes. While the dc field offers flexibility in efficient, tunable laser design, the required field strengths for visible radiation are in the megavolt/meter range.     

COMPARISON BETWEEN FEL AND CYCLOTRON RADIATION

In general,in free electron lasers there are two kinds of stimulated radiations:FELradiation and cyclotron radiation.This paper chows theoretically that if the initial transversevelocity of electron beam is large and the selected parameters for FEL are not suitable,thecyclotron radiation will be dominant,especially when the energy of electron beam is low.But thecyclotron radiation does not have double Doppler frequency upshift effect,its frequency is limitedby axial megnetic field,and when the energy of electron beam is high,the cyclotron radiationfrequency will be much lower than FEL radiation frequency.Therefore,in FEL experimentshow to distinguish these two kinds of radiations and to suppress the cyclotron radiation are veryimportant.     

电子束与等离子体互作用产生的宽带微波辐射

近年来，电子束与等离子体互作用产生高功率宽带微波辐射，由于其具有可调谐等优点而受到国际上普遍关注，这一互作用过程的辐射机制目前大致分为等离子体辐射和电子束辐射两大类，本文在简介了有关实验情况后，对几种辐射机制，包括逆Ｃｏｍｐｔｏｎ散射，孤立子场中群聚电子的辐射，非线性等离子体电流引起的辐射等作了评述。     

自由电子激光辐射和迴旋辐射的比较研究

在自由电子激光器中一般存在两种受激辐射形式:自由电子激光辐射和迴旋辐射。本文从理论上阐明,如果电子束的初始横向速度较大,自由电子激光器的参数选用不当,则迴旋辐射将占优势,特别当电子束能量较低时,产生迴旋辐射的倾向更大。但是迴旋辐射并不具有双重多普勒频率上漂移的特性,由于受轴向磁场强度的限制,在电子束能量较高时,其辐射频率要比自由电子激光辐射频率低得多。因此在自由电子激光器的实验研究中,如何区别这两种辐射,并有效地抑制迴旋辐射,是一个十分重要的课题。     

Phase variation in free-electron laser amplifiers

The evolution of the phase of the output radiation of free-electron laser amplifiers is investigated by means of a three-dimensional simulation code. The configuration employed consists of the propagation of a relativistic electron beam through a loss-free cylindrical waveguide in the presence of a helically symmetric wiggler and a uniform axial guide magnetic field. The analysis is fully three dimensional, and a set of model equations is discussed which describes the coupling between an ensemble of electrons and the radiation field of either the TE or TM modes. The model equations are solved numerically, and the output phase is studied with respect to variations in either frequency or electron beam energy. The output phase is found to depend sensitively on the wave frequency within the unstable bandwidth. In addition, the phase stability of the output radiation is discussed as a function of beam energy. Finally, the evolution of the phase for tapered wiggler free-electron lasers is studied.     

自由电子激光中自发辐射光脉冲的自干涉现象

本文用格林函数法,计算了螺旋磁场自由电子激光中单脉冲电子注的自发辐射;结果表明,电子注的有限长度会引起自发辐射光脉冲的自干涉现象。     

碳纳米管冷阴极Pierce电子枪

为发展场致发射冷阴极毫米波电真空辐射源器件, 对利用大面积碳纳米管冷阴极产生大电流、高电流密度电子注的电子光学系统进行了研究.通过在Pierce电子枪阴极表面引入栅网结构, 解决了碳纳米管冷阴极场致发射所需的强电场和电子聚束问题.在碳纳米管冷阴极实验测试数据的基础上, 采用粒子模拟软件对上述电子光学系统进行了仿真.研究了栅网对注电流、注腰半径和电子注散射的影响, 分析了阳极电压和外加轴向磁场对电子注的聚束作用.优化后的仿真结果表明在阴极发射面为3.03 cm2时, 该电子光学系统能够产生210 mA、60 kV, 电流密度为6.7 A/cm2, 最大注半径为1mm的电子注.     

康普顿型自由电子激光光导效应理论研究

对康普顿型自由电子激光（ＦＥＬ）光导效应进行了理论分析和数值计算。推导出适用于三维自由电子激光器中的电子束的等效折射率，说明高斯平面波激光场是电子束等效折射率按平方律分布即类透镜介质的结果。对自由电子激光强度和相位分布、光束半径以及等效折射率等进行了数值模拟，并对模拟结果进行了分析。     

Magnetic field profiles in depressed collector region for small-orbit gyrotrons with axial or radially extracted spent beam

Feasibility studies for the design of multiple depressed collectors for small-orbit gyrotrons are presented. Particular attention is paid to the effect of profiles of magnetic field on the electron trajectories. Two cases are considered involving alternative approaches to separating the paths of the spent beam and the output radiation. In the first example the beam proceeds axially while the radiation is coupled out radially. A magnetic field profile that is neither purely adiabatic nor purely non-adiabatic is shown to give energy sorting and collection of beamlets without reflection of the particles, while keeping the outermost radius of the collector within reasonable limits. Studies are also presented of electron trajectories of a radially directed beam in the collector region. It is seen that the magnetic field must have a very low value and its configuration must be tailored over a wide region, A magnetic circuit consisting of a shield and a number of independently controlled coils is described which can produce such a field configuration. Results of trajectory tracing are presented showing energy sorting and collection without reflection.     

强流相对论电子束环产生的毫米波相干辐射

本文研究由跃变磁场产生的绕轴高速旋转的电子束环(E层)产生毫米波相干辐射的特性。我们采用符拉索夫-麦克斯韦方程分析E层与磁控管腔的相互作用,导出色散关系,并进行了数值分析。结果表明,微波幅射频率为r=l∥(其中∥是电子在轴向磁场中的相对论迴旋频率;l是方位角方向上的模数,l=n+mN,N是磁控管腔的边腔数,n=0,1,2,,N/2,m是任意整数),而且l很大时辐射仍有足够高的增长率。这有利于在低的轴向磁场中产生毫米波辐射。如能很好地解决模式控制问题,就能做成低磁场的可调谐大功率毫米波器件。     

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.     

The long pulse effect in FEL's

The paper, by means of Green's function and Fourier spectral theory, investigates spontaneous radiation of a single pulse electron bean in free electron lasers with a helically periodical magnetic field. It is found that there are fast and slow electroagnetic waves as well as normal in the interaction region, and that the energy spectrum of spontaneous emission is not only dependent on the imposed helical field, but also modulated sensitively by the electron beam pulse. Under some conditions, the spectrum may have main peaks more than one, showing oscillations, that is, the long pulse effect.     

环形相对论电子注激励的等离子体介质切伦可夫脉塞

利用自洽线性场理论，考虑电子的三维扰动，分析了环形相对论电子注在填充背景等离子体的介质筒慢波波导产生的切伦可夫辐射，其环形电子注对主波互作用的作用完全要用一跳变条件来描述，导出了其色散方程和波波互作用的同步条件，求得了是子注产生的波增长率，分析了背景等离子体密度和电子注半径对波增长率的影响。     

Theory and simulation of an 85 GHz quasioptical gyroklystron experiment

The linear theory used to design a two-resonator 85 GHz quasioptical gyroklystron with a nonuniform magnetic field is presented. It is shown that a tapered magnetic field in the prebunching resonator has a relatively small effect on the electron bunching parameter. The effect of velocity spread of the electron beam can be minimized by adjusting the magnetic field strength in the two resonators. Measured amplifier performance is in good agreement with calculations from the nonlinear multimode simulation code. Gyrophase bunching of the electrons is preserved over the long drift region (30 radiation wavelengths) even though no attempt has been made to minimize the velocity spread of the beam.     

ON ENERGY CONSERVATION IN RADIATION PROCESS OF ELECTRON BEAM WITHIN A WAVEGUIDE SYSTEM

The formula for the electromagnetic field induced by electron beam in a waveguide witharbitrary cross-section has been derived by using the operator theory of electromagnetic field.In this formulathe normalized eigen function in ordinary dyadic Green's function is replaced by the field induced by unitpower flow.By this formula,the relationship of energy conservation in the radiation process can be proyedeasily and it can be used in the interaction theory for different microwave electron tubes.     

A submillimeter free-electron laser experiment

A free-electron laser (FEL) Raman-backscattering oscillator, using afrac{1}{2}-1MeV, 20 kA electron beam pumped with a weak (∼ 250g) periodic (8 mm) transverse magnetic field, is operated as a source of high power millimeter and submillimeter radiation, with lasing developing during the 150 ns beam pulse. Measurements of lasing operation are described at 1.0 and 0.6 mm. The temporal behavior of cavity radiation is considered and effective gain is measured and compared with theory.     

Multiwave Cherenkov generator with linearly polarized radiation

A multiwave Cherenkov generator with an asymmetric superdimensional slow-wave structure that generates the linearly polarized radiation is proposed and experimentally studied. The pulses of the linearly polarized radiation with a wavelength of 3.25 cm, a pulse duration of 30 ns, and a power of 850 MW are generated at electron energy of 470 keV and a beam current of 4.9 kA in a relatively weak magnetic field of 4.3 kG. It is demonstrated that the generation efficiency is 30% for almost Gaussian field distribution.     

实心注在等离子体介质筒产生的切伦可夫辐射

利用自洽线性场理论：考虑电子的三维扰动，分析了轴向实心相对论电子注通过填充背景等离子体介质筒慢波波导产生的切伦可夫辐射，导出了描述其不稳定性的色散方程和注液互作用的同步条件，求得出电磁波辐射的时间增长率，分析了背景等离子体密度和实心电子注半径对波增长率的影响。