Powerful electromagnetic millimeter-wave oscillations produced by stimulated scattering of microwave radiation by relativistic electron beams

The stimulated scattering of electromagnetic waves in microwave generators, in which a high-current electron beam excites either a backward wave (BWO) or a quasi-critical frequency wave (orotron) is investigated experimentally. The scattering occurs at the same electron beam and the high-frequency feedback is provided by the inhomogeneities of the electrodynamic system of the microwave generator itself. A power of several tens of megawatts has been achieved in the 3-mm range. The mode selection permitted to obtain single-mode scattering.     

速调型相对论返波管理论研究

对速调型相对论返波管慢波结构色散特性及束波相互作用进行了理论研究。色散特性研究表明:器件工作模式为TM01模,近点,耦合阻抗较高。色散特性预测的工作频率与粒子模拟结果非常接近。慢波结构峰值增长率相对较小,这与电子束与慢波结构相距较大有关,因而器件从起振到饱和的时间较长。在束波相互作用理论中,全面考虑了电子束与慢波结构前向波基波、反向波－1次空间谐波及空间电荷场相互作用、谐振反射器对电子束进行的束流调制和能量调制作用,以及调制腔和提取腔处引入的耦合阻抗及轴向波数突变。稳态和非稳态计算结果均获得了超过40%的束波转换效率。     

具有双电子束结构的双波段相对论返波振荡器粒子模拟研究

研究了一种能够同时产生C波段和X波段微波、具有双电子束结构的相对论返波振荡器,采用嵌套式的高频结构将两个波段的束-波相互作用空间隔离开来,从而使两个波段的束-波相互过程互不影响。当二极管电压为650 kV、内外环形电子束流分别为5.4,6.4 kA、导引磁场为2.2 T时,两个波段微波的频率分别为4.625,8.450 GHz,模拟产生的微波功率分别为920,600 MW,转换效率约为21.8%,17.1%。并采用粒子模拟法研究了导引磁场、二极管电压及两个束-波相互作用区关键结构参数对器件运行的影响,给出了双波段微波功率、频率随导引磁场、二极管电压等参数的变化曲线。     

具有双电子束结构的双波段相对论返波振荡器粒子模拟研究北大核心CSCD

研究了一种能够同时产生C波段和X波段微波、具有双电子束结构的相对论返波振荡器,采用嵌套式的高频结构将两个波段的束-波相互作用空间隔离开来,从而使两个波段的束-波相互过程互不影响。当二极管电压为650kV、内外环形电子束流分别为5.4,6.4kA、导引磁场为2.2T时,两个波段微波的频率分别为4.625,8.450GHz,模拟产生的微波功率分别为920,600MW,转换效率约为21.8%,17.1%。并采用粒子模拟法研究了导引磁场、二极管电压及两个束-波相互作用区关键结构参数对器件运行的影响,给出了双波段微波功率、频率随导引磁场、二极管电压等参数的变化曲线。     

介质加载的矩形截面Cerenkov脉塞中带状电子注与慢波结构互作用的研究

本文建立了介质加载的矩形截面Cerenkov脉塞中带状电子注与慢波结构互作用的三维物理模型. 采用Borgnis函数法和场匹配法求解了多层介质中场的匹配问题, 获得了注波互作用结构的混合模热色散方程(含电子注)及其近似解. 通过数值计算, 分析了热态下介质层厚度、电子注电压、电流密度、电子注厚度及电子注与 介质层间隙距离等主要结构和电参数对注波互作用增长率的影响.     

基于切伦科夫辐射的核素治疗剂量测量可行性分析

针对现有核素治疗中内照射剂量测量缺乏简单、高效方法的问题,基于内照射剂量与切伦科夫辐射之间的关系,提出一种基于切伦科夫辐射的核素治疗内照射剂量测量的新方法。利用蒙特卡罗计算程序Geant4,模拟放射性核素131I在水体模型和甲状腺模型中产生切伦科夫辐射与剂量沉积的分布情况,并定量分析切伦科夫光子数与剂量之间的关系。计算结果表明：在水体模的半径方向上切伦科夫光子数与剂量之间有着相同的变化趋势,且两者有着相同的二维分布规律;核素131I在介质中产生的切伦科夫光子数与剂量两者之间存在一定的线性关系,且这种线性关系与核素的分布情况无关。研究结果证实,将这种放射性核素在介质中产生的切伦科夫辐射应用于内照射剂量学具有非常大的研究潜力和价值。     

等离子体中相对论电子的同步曲率辐射特性研究

根据同步曲率辐射理论推导了在等离子体环境中,不同磁场条件下的相对论性电子的吸收系数和发射系数表达式，计算了电子的发射强度，并且在此基础上研究了同步曲率辐射机制的脉泽效应.研究了两种磁场位型，第一种是强度均匀但弯曲的磁场，第二种是偶极磁场，结果发现了一些偶极磁场下特有的辐射特性.考虑到在天体的环境下电子具有的不同的能谱分布，分别选用了三种典型的能谱分布(幂率分布，高斯分布，热分布)进行了研究，通过计算负吸收和脉泽放大效应在发射强度上的表现后， 发现在某些天体物理环境中，同步曲率辐射在等离子体中的确存在脉泽放大效应.这些研究结果对太阳系中行星外层辐射的研究和宇宙中的射电高亮温度等问题的研究可能提供有益的帮助. 关键词： 同步曲率辐射 负吸收 脉泽效应     

相对论电子束在角向磁场中产生硬X射线的实验研究

 在闪光二号加速器上用相对论电子束在低压气体和角向磁场中传输打靶的方法，进行了硬X射线产生的实验研究。在47cm传输距离上，电子束与钽靶作用，获得了面积积分剂量率为2.1×10¹⁰Gy·cm²/s的硬X射线辐射（能谱范围为20～120keV），在总的辐照面积上(4π方向)面积积分剂量达1 843Gy·cm²，X射线转换率达到108Gy·cm²/kJ。     

Spectrum broadening effect in coherent x-ray radiation of a relativistic electron crossing a single-crystal plate

Based on the dynamic diffraction theory [1], coherent x-ray radiation of a relativistic electron crossing a single-crystal plate at a constant velocity is considered in the Bragg geometry. In the general case of asymmetric reflection of the radiation from the target, expressions are derived for the spectral-angular distribution of parametric x-ray radiation (PXR) and diffraction transition radiation (DTR). For a fixed angle between the electron trajectory and the system of parallel atomic planes of the crystal (Bragg’s angle) it is shown that a decrease in the angle of electron incidence on the crystal plate gives rise to a significant increase in the PXR and DTR spectra, and the causes for spectral broadening for each of these radiation mechanisms are different. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 74–83, March, 2009.     

Development of the relativistic backward wave oscillator with a permanent magnet

Firstly, an X-band relativistic backward wave oscillator with a low guiding magnetic field is simulated, whose output microwave power is 520 MW. Then, an experiment is carried out on an accelerator to investigate a relativistic backward wave oscillator with a permanent magnetic field whose strength is 0.46 T. When the energy of the electron is 630 keV and the current of the electron beam is 6.7 kA, a 15 ns width pulsed microwave with 510 MW output power at 8.0 GHz microwave frequency is achieved.     

内导体对相对论返波振荡器工作波段选择的影响

 设计了一种紧凑型、GW级同轴引出电子束相对论返波振荡器,利用KARAT 2.5维全电磁粒子模拟程序研究了器件内部束 波作用的物理过程。模拟结果表明：当器件中使用内导体,在电子束能量700 keV,电子束流11 kA,导引磁场为1.0 T时,能实现L波段2.66 GW高功率微波输出,平均效率约为34%;去掉内导体时,能实现S波段1.88 GW单频微波输出,平均效率约为24%。同一个器件,仅通过装卸内导体就可以选择在两个波段实现GW级、高效微波输出,这对于高功率微波器件的设计有一定的参考意义。     

Design of a new compact THz source based on Smith-Purcell radiation

In recent years, people are dedicated to the research work of finding compact THz sources with high emission power. Smith-Purcell radiation is qualified for the possibility of coherent enhancement due to the effect of FEL mechanism. The compact experiment device is expected to produce hundreds mW level THz ray. The electron beam with good quality is provided under the optimized design of the electron gun. Besides, the grating is designed as an oscillator without any external feedbacks. While the beam passes through the grating surface, the beam bunching will be strong and the second harmonics enhancement will be evident, as is seen from the simulation results.     

离子通道中相对论电子注的切连科夫辐射

对入射等离子体的相对论电子注(REB)在离子通道中可能产生切连科夫(Cherenkov)辐射的问题进行了论证与研究.利用线性理论分析了离子背景下的注-波互作用关系，导出了系统的色散方程与同步辐射条件.结果表明，系统的电磁不稳定性是由离子通道中TM模与电子注模通过电子注耦合所致，其微观机理是离子对电子注的聚焦.对处于运动等离子体状态下的离子-注系统进行了严格地理论分析，获得了通道内辐射波的频偏与波增长率公式，并通过数值模拟计算讨论了系统有关参数对它们的影响. 关键词： 离子通道 等离子体 切连科夫辐射     

The interaction of relativistic electron beam with the electromagnetic field in the neighbourhood of a caustic region

We present the theory of self-consistent interaction of crooked relativistic electron beam within and near the e.m. field caustic zones of jumping ball and whispering gallery types being formed in open resonators of elliptical cylindrical symmetry. On the basis of numerical analysis of nonlinear system of equations by applying a large-particles method, the principal possibility to design the multiwave synchro-Cherenkov amplifiers and generators is shown.     

利用超快电子探针诊断受激拉曼散射静电波的数值模拟

利用二维粒子模拟程序EPOCH验证了超快电子束探针诊断受激拉曼散射产生的静电波的可行性。结果表明,电子束探针穿过静电波电场后会在电子束探针的横向上产生密度调制,密度调制呈周期性分布且沿静电波的传播方向移动,密度调制的波数对应静电波的波数且移动速度对应静电波的相速度,因此特定条件下可用于反推电子的温度、密度等信息。在诊断静电波的过程中,电子束探针的束长必须小于静电波的波长或者诊断设备的曝光时间必须小于静电波的周期。本研究提供了一种新型的直接诊断静电波和电子温度、密度的方法,对于推动受激拉曼散射等激光等离子体不稳定性的实验研究具有重要意义。     

The study on optically stimulated luminescence dosimeter based on the SrS：Eu,Sm and CaS：Eu,Sm

With the increasing use of nuclear energy, there is a need for a wider range of efficient dosimeters for radiation detection and assessment. There has been a tremendous growth in the development of radiation detectors and devices in the past few decades. In recent years, the development of new materials for radiation dosimetry has progressed significantly. Alkaline earth sulfides （AES） have been known for a long time as excellent and versatile phosphor materials. In the present investigation, a number of phosphor samples such as mono-, binary and ternary sulfides of alkaline earths （II^a-VI^b） have been prepared and their TL properties have been studied with respect to exposure （x-ray） response and fading. In this paper, some results on SrS：Eu, Sm and CaS：Eu, Sm phosphors are presented. A type of novel OSL dosimeter is described. The dosimeter takes advantage of the characteristics of charge trapping materials SrS：Eu, Sm and CaS：Eu, Sm that exhibit optically stimulated luminescence （OSL）. The measuring range of the dosimeter is from 0.01 to 1000 Gy. The OSL dosimeters provide capability for remote monitoring radiation locations which are difficult to access and hazardous. This equipment is relatively simple, small in size and has low power consumption. The device is suitable for space radiation dose exploration. In addition, it also can be used in IC and other radiation occasions and has good prospects.     

单模块直线变压器脉冲前沿

从理论上对直线变压器驱动源（LTD）输出脉冲波形的前沿进行了分析,研究了不同前沿畸变情况下对应的电路参数,并给出了计算方法,得到了相对电压和相对时间的关系曲线。根据理论分析设计了单模块LTD,并根据设计参数进行了数值模拟,模拟得到的输出脉冲前沿约30 ns、平顶约130 ns、幅值约125 kV。最后进行了单模块LTD实验,测得输出脉冲前沿约35 ns、平顶约130 ns、幅值约125 kV的输出脉冲,与模拟结果基本一致。由于负载不完全匹配等因素的影响,波形后沿较差且有振荡,但仍符合设计要求。     

Effect of external magnetic field on critical current for the onset of virtual cathode oscillations in relativistic electron beams

In this Letter we research the space charge limiting current value at which the oscillating virtual cathode is formed in the relativistic electron beam as a function of the external magnetic field guiding the beam electrons. It is shown that the space charge limiting (critical) current decreases with growth of the external magnetic field, and that there is an optimal induction value of the magnetic field at which the critical current for the onset of virtual cathode oscillations in the electron beam is minimum. For the strong external magnetic field the space charge limiting current corresponds to the analytical relation derived under the assumption that the motion of the electron beam is one-dimensional [D.J. Sullivan, J.E. Walsh, E. Coutsias, in: V.L. Granatstein, I. Alexeff (Eds.), Virtual Cathode Oscillator (Vircator) Theory, in: High Power Microwave Sources, vol. 13, Artech House Microwave Library, 1987, Chapter 13]. Such behavior is explained by the characteristic features of the dynamics of electron space charge in the longitudinal and radial directions in the drift space at the different external magnetic fields.     

Modeling of terahertz radiation emission from a free‐electron laser

In this article, we report the generation of terahertz (THz) radiation using the interaction of a laser‐modulated relativistic electron beam (REB) with a surface plasma wave. Two laser beams propagating through the modulator interact with the REB, leading to velocity modulation of the beam. This results in pre‐bunching of the REB. The pre‐bunched beam travels through the drift space, where the velocity modulation translates into density modulation. The density‐modulated beam, on interacting with the surface plasma pump wave, acquires an oscillatory velocity that couples with the modulated beam density to give rise to a nonlinear current density which acts as an antenna to give THz radiation. By optimizing the parameters of the beam and the wiggler, we obtain power of the order of 10⁻⁴ using the current scheme.