新型史密斯-帕塞尔自由电子激光实验

介绍一种新型的Smith PurcellFEL实验 ,实验中利用中等能量级的相对论电子束激励 ,由衍射光栅和三反射镜组成的新型准光学系统 ,可以产生可调短毫米波、远红外波段的辐射。主要实验参数为 :电子注能量为 40 0～ 5 0 0keV ,电压脉冲宽度 70ns ,同步脉冲磁场强度 1.2T ,成功地检测到 3mm波段的毫米波信号 ,其峰值功率达到数十千瓦     

A Novel Smith-Purcell FEL

A novel Smith-Purcell FEL with a relativistic electron beam of middle energy and a quasi-optical resonator composed of diffraction grating and three mirror reflector is described in this paper. Coherent radiation with peak power of tens of KW at 3 mm waveband is successfully detected from an experimental facility characterized by beam energy of 400-500 KeV, pulse length of 70 ns, pulse beam current of 0.2 KA, and pulse guide magnetic field of up to 1.2 T.     

Free electron laser based on the Smith-Purcell radiation

The electromagnetic radiation is sti mulated when anelectron beampasses a metallic periodic structure like adiffraction grating at a fixed distance close to the sur-face.This phenomenon is known as the Smith-Purcelleffect .The radiation mechanism was pred…     

软X射线自由电子激光单色器优化方法

软X射线自由电子激光(FEL)光栅单色器的设计是个多目标优化任务,涉及到能量分辨能力、脉冲展宽、光斑投影大小、物距、像距、光栅线密度、光栅变线距等众多参数,优化起来十分复杂。本文提出了光栅单色器的统一优化方法模型,该模型把多目标优化任务转化为单目标(光栅焦点常数C_ff)优化任务。基于该模型,本文对比了三种软X射线FEL光栅单色器设计方案,并直观地对单色器能量分辨能力、脉冲展宽和光斑在光栅上投影大小进行评估。此外对这三种光栅单色器的设计方案进行了详细的计算,并绘制出了“C_ff-波长-优化参数”三元图。通过“C_ff-波长-优化参数”三元图,能够清晰地得到光栅单色器的能量分辨能力、脉冲展宽和光斑投影大小随着C_ff变化而变化的趋势。本项工作为光栅单色器的设计和优化提供指导作用。     

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。     

W波段带状注速调管电子光学系统的研究进展

带状注速调管以其在毫米波段可获得高功率和高增益输出,以及小型化、紧凑型、平面微加工成形等的技术优势而备受国际前沿领域广泛关注。本文重点给出了正在开展的W波段带状注速调管的研究工作,通过采用均匀场聚焦的带状电子注的方式,研制出了椭圆截面带状电子注成形与传输的束流样管。通过实验测试获得的电子枪压缩和成形的带状电子注截面为10 mm×0.7 mm,且在电子注电压为20~82 kV,电流0.5~4.27 A时,长度为100 mm的漂移通道内电子注传输的直流通过率达到98%以上,从而验证了采用均匀场传输带状注的方案是完全可行的。     

自由电子激光器的一些改进方案

自由电子激光器(FEL)能否充分发挥其优异特性而走向实用,最终将取决于器件能否小型化.作者对现有喇曼自由电子激光器的控制系统及加速器部分进行了改进,使其体积大为减小,并对小型化FEL的设想进行了总体布局.     

G 波段带状注速调管电子光学系统的初步设计

设计了G 波段带状注速调管电子光学系统,主要工作参数为：电子注电压16.5kV,电流0.58A。电子注通道截 面3.272mmx0.274mm,通道长度20mm。阴极面是曲率半径为5mm 的矩形柱面,尺寸为2.5mm×1.2mm,电子注在单一 方向上压缩,电子注束腰截面尺寸2.5mm×0.12mm,电子枪压缩比10:1。采用均匀场聚焦方式,模拟了三种磁场强度下 的电子注成形和传输过程。模拟结果显示,电子注传输的Diocotron 不稳定现象在强磁场下得到改善;磁场强度为8700Gs 时的传输通过率为100%。     

Simulations of a ring resonator free-electron laser

A relatively high gain (≈25 to 40%) free-electron laser (FEL) with an optical ring resonator is simulated using the code FELEX. The laser system corresponds to the `burst mode' FEL. The ring consists of paraboloids, grazing incidence hyperboloids, and a grating rhomb. The wiggler is 5 m in length and has an adjustable taper, while the electron beam is produced by an RF linac. The optical elements of the ring together with the FEL interaction in the wiggler are modeled in three spatial dimensions to investigate the system from start-up to saturation. Both single-frequency and finite-pulse simulations are performed     

Stimulated emission by E×B drifting electrons grazing adiffraction grating

It has been recently proposed that generation of relativistically upshifted radiation by an E×B drifting electron beam grazing a diffraction grating combines the Smith-Purcel free-electron laser (FEL) merits of short wavelengths at low beam energies, with efficiencies much higher than the 1/2 N_g conventional FEL limit. The small-signal theory is studied here, including the effect of drift velocity shear from the equilibrium (unbunched) space-charge fields. The dependence of the small-signal gain on the device parameters is determined and the startup current is evaluated. The effect of thermal beam spreads is analyzed and found that the oscillation startup current is much less sensitive to thermal spreads than a similar grating FEL     

X 波段高功率带状注速调管电子枪的研制

介绍了为新型高功率速调管研制的能产生矩形截面束流的带状注电子枪,其设计工作电压300kV,工作电流330A,导流系数约2.0μp,矩形柱面阴极100mm×40mm,经一维压缩形成的束流截面尺寸为100mm×8mm,电子注的层流性较好。按照设计值制成了带状注电子枪密封管并对其性能进行了测试,初步的实验结果表明电子枪的电性能指标达到了设计要求。     

FEL驱动激光器的研究

为了获得高亮度和高品质的电子束,在自由电子激光实验装置中采用光阴极注入器作为电子源,其驱动激光器系统采用主振功率放大结构,振荡器为二极管抽运连续锁模激光器,放大器为一级双程及两级单程二极管脉冲抽运放大,后接4倍频系统.经过工程研制及调试,获得的输出指标为:波长266nm,微脉冲能量4μJ,宏脉冲宽度2μs至6μs可调,微脉冲能量抖动优于3%.结果表明,采用Cs2Te阴极的光阴极注入器实验,该系统能够获得不低于40A的电子束流,达到了自由电子激光实验对电子源的束流要求.     

自由电子激光器输出性能的研究

研究了自由电子激光器的输出功率,指出红外波段的自由电子激光器将较紫外波段器件容易获得高功率输出;讨论了相对论电子束的脉冲宽度和共振腔透过率的选择,获得了超辐射输出的工作条件;讨论了相对论电子束能量发散度Δγ_0/γ_0对激光能量转换效率的影响。     

新型史密斯-帕塞尔效应可调辐射源研究

提出采用中等能量的相对论环状电子注激励轴对称三曲面反射镜、绕射光栅系统，产生毫米波、远红外波段辐射的新型准光学可调辐射源实验方案，这是一种基于史密斯一帕塞尔效应的自由电子激光。由于引入新型准光学谐振腔系统，可以改变能量输出方向的角度，从原理上讲，可制造一系列模型，产生可调频率的短毫米波、远红外波段相干辐射。采用环状电子注比带状电子注稳定性高，便于成型和聚焦；采用新腔体后增长了电子注与高频场的互作用范围；新型准光腔具有较小的绕射损耗。新方案的这些特点，进一步提高器件的输出功率，改善了高频特性。介绍这种新辐射源在3mm波段的粒子模拟计算初步结果，其输出功率达数百千瓦以上；同时给出准光学谐振腔高频系统的模拟计算和冷测实验的典型曲线。     

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.     

Experimental and theoretical study of periodic intensity bursts inthe start-up phase of a free-electron laser oscillator

Experimental observations and a theoretical analysis of periodic radiation bursts and macropulse formation in the startup phase of a free-electron laser (FEL) oscillator are presented. This microwave FEL uses a long pulse electron beam with a slowly decaying voltage. The output radiation consists of a superposition of bell-shaped macropulses, each of which is composed of a periodic sequence of short micropulses. The micropulses are separated by a cavity round-trip time. Each bell-shaped macropulse has a random startup time and amplitude. The startup of the radiation macropulses is correlated with random current spikes on the continuous electron beam. The observed macropulse signal agrees with a theoretical calculation of the impulse response of the FEL oscillator when the shift in the FEL resonance frequency arising from the slow voltage drop of the electron beam is included in the analysis. Possible applications of the macropulse formation phenomena in the FEL are discussed     

带状电子注聚焦系统设计

通过理论分析、数值模拟和实验研究了PCM 结构聚焦椭圆带状电子注的可行性。利用三维PIC 粒子模拟软 件模拟了椭圆带状电子注在PCM 结构行程的周期磁场中的传输过程,结果显示：截面为10x0.4 mm2 的椭圆带状电子 注在12x0.8 mm2 的矩形通道中稳定长距离传输120mm 无截获。对PCM 聚焦结构的磁场进行了测试,测试结果与数 值模拟结果相符。实验并研究了该PCM 聚焦系统约束带状电子注的能力,测试用速调管的设计电压为75kV,在56.8kV 时的直流通过率达到52.1%,并随着工作电压的升高呈上升趋势。     

有限尺寸光栅压缩器的优化设计

分析了超短超强激光系统中有限尺寸光栅压缩器设计的关键物理参数及约束条件,得到了压缩器优化的三项基本变量。给出了一种输出能量最大化的压缩器优化方法,进而确定了有限尺寸光栅压缩器的最大工作能力。针对传统的圆光束方案提出了改进的椭圆光束方案,增大了聚焦能量,减小了焦斑尺寸,提高了峰值聚焦功率密度。通过数值模拟对500 mm曝光口径介质膜光栅在圆光束和椭圆光束两种方案下的最大输出能力进行分析比较,指出单块光栅在椭圆光束方案下可以实现500 fs,500 J,1 PW的脉冲输出。     

360 GHz返波管的研究

对采用齿状光栅结构的慢波电路进行了研究,该结构在电子束与光栅表面接近的情况下有一定的通过率。在求得最大耦合阻抗条件下,设计了一种工作在360 GHz的返波管,通过对互作用电路的耦合阻抗的分析,可以减小亚毫米波及太赫兹真空电子学辐射源对阴极发射电流密度的要求。当工作电压为19.5 kV,工作电流75 mA时,PIC模拟结果得到了8 W的平均功率输出,考虑阴极为脉冲工作时,该器件在360 GHz可以得到4 mW的平均功率输出。     

Design of a compact, optically guided, pinched, megawatt class free-electron laser

A conceptual design for a compact megawatt class free-electron laser (FEL) operating at 1 /spl mu/m is presented. The proposed FEL consists of an optically guided, pinched amplifier configuration driven by a RF linac. The gain length, efficiency, electron pulse slippage, and the distance between the wiggler and first relay mirror are determined for a megawatt class design. Of particular concern in the design is the overall length of the optical system, i.e., the wiggler length and distance to the first relay mirror. In the present design, the wiggler length is /spl sim/1 m and the distance between the first relay mirror and the wiggler is determined by the average intensity damage threshold on the mirror. By focusing the electron beam, the optical beam can be pinched upon exiting the wiggler. The pinched optical beam has a reduced Rayleigh length which permits the first relay mirror to be relatively close to the wiggler. By pinching the optical beam and employing grazing incidence the first relay mirror can be located within /spl sim/3 m of the wiggler. It is shown that frequency detuning can more than double the FEL efficiency. In the present design with frequency detuning and uniform wiggler the efficiency is /spl sim/1.8%. In addition, electron-pulse slippage is shown to be substantially reduced in a high-gain amplifier.