The Design of Megawatt Gyrotrons

The design parameters of a 120-GHz gyromonotron capable of output powers in excess of 1 MW are determined. A nonlinear model of the interaction between the beam and RF field is used in which the efficiency is a function of only three normalized variables. By expressing the technological constraints in terms of these variables, permissible design parameters yielding high-efficiency operation can be calculated. Constraints that are considered include ohmic heating of the walls, voltage depression of the beam, reduced coupling between the beam and RF field due to beam thickness, and efficiency degradation due to space-charge forces within the beam. An analysis of the trade-offs between current and voltage at the 1-MW level indicates that lower-order modes can be utilized at lower voltages, but the constraints based on current limitations are difficult to satisfy. An 80-kV 29-A design is presented that achieves a total efficiency of 44 percent. The primary uncertainty of these designs is the severity of competition due to parasitic modes. However, a number of isolated asymmetric modes appear capable of single-mode emission at 1 MW based on present experimental results. Multimegawatt operation is also considered. It is shown that powers exceeding 20 MW are possible if single-mode operation can be achieved in very-high-order modes. The methodology presented in this paper is general and can be easily adapted to other frequencies and output powers.     

螺旋线行波管1维多频非线性理论与模拟

 采用CHRISTINE报告中的1维多信号非线性互作用模型,在其场方程、相位方程和含空间电荷场的运动方程的表达式基础上,增加了切断区域的工作方程组,并考虑了电位下沉带来的影响。基于此非线性互作用工作方程组编写了数值计算程序。为了便于对行波管互作用进行模拟设计时选择最佳工作电压和输入功率,在程序中加入了扫描电压和输入功率的功能。对某行波管注波互作用过程进行了模拟,并分析了谐波和互调的影响。由于计算速度快,模拟结果较好,对螺旋线行波管的初步设计和验证具有较强的指导意义。     

Analytical solution to the transient beam loading effects of a superconducting cavity

Transient beam loading is one of the key issues in any high beam current intensity superconducting accelerators, and needs to be carefully investigated. The core problem in the analysis is to obtain the time evolution of effective cavity voltage under transient beam loading. To simplify the problem, the second order ordinary differential equation describing the behavior of the effective cavity voltage is intuitively simplified to a first order one, with the aid of two critical approximations which lack proof of their validity. In this paper, the validity is examined mathematically in some specific cases, resulting in a criterion for the simplification. It is popular to solve the approximate equation for the effective cavity voltage numerically, while this paper shows that it can also be solved analytically under the step function approximation for the driven term. With the analytical solution to the effective cavity voltage, the transient reflected power from the cavity and the energy gain of the central particle in the bunch can also be calculated analytically. The validity of the step function approximation for the driven term is examined by direct evaluations.After that, the analytical results are compared with the numerical ones.     

电子束收集极对大间隙速调管输出腔效率的影响

 利用高频电磁软件对带电子束收集极的S波段大间隙输出腔进行了高频特性分析,采用3维PIC程序模拟了电子束收集极对大间隙速调管输出效率的影响。研究结果表明：收集极的存在会改变输出腔的本征谐振频率和电子束路径上的特性阻抗等高频特性,但收集极可以短路间隙附近的径向电场,减小电子束的空间电荷压力,同时对群聚电子进行再加速,从而提高大间隙速调管的输出效率;在束电压700 kV,直流电流6 kA时,优化后的带收集极的大间隙输出腔可稳定提取大于1.68 GW的微波功率,提取效率约40.1%,比无收集极时提高约5%。     

Investigations of electron beam induced conductivity in silicon oxide thin films

Silicon oxide thin film conductivity under electron beam irradiation is studied. An induced current in the films is varied in a range from a few tenths to a few values of the beam current. The dependence of the current normalized to a product of the applied voltage and the beam current on the beam energy is found to have a maximum determined by the film thickness, beam energy, and sign of the applied voltage. For the negative voltage applied to the metal electrode deposited on the film, this maximum is observed at the beam energy, at which the depth generation function is smaller by several tens of nanometers than the film thickness. For the positive voltage on the metal electrode, the maximum is observed at higher beam energies. The obtained result could be qualitatively explained under the assumption that a stationary excess carrier distribution is formed under the electron beam. This distribution is shifted with respect to the generation function due to diffusion and drift of excess carriers. A value of this shift is of about a few tens of nanometers, and its sign indicates that the majority carriers providing the induced conductivity in the films studied are electrons.     

Voltage-controlled optical switch in planar nematic liquid crystal film

This study presents an integrated device that consists of a directional coupler and an electro-optic switch. The device is designed to include a nematic liquid crystal cell, comprising a grating-like electrode. Applying the appropriate voltage to the cell yields a periodically distributed refractive index. An incident polarized beam will couple to an adjacent channel if it is parallel to the channel. The coupling efficiency is controlled by applied voltage. An obliquely injected polarized beam will be reflected and refracted in the channel, and propagated along a curved path. The route of the beam can be controlled by applying the voltage. A multiport routing was achieved for voltage modulation. In addition, the distribution of refractive index is also investigated by employing conoscopic technique experimentally and numerically.     

Experimental Study on Electrostatic with Two Guiding of Supersonic D20 Molecular Beam Charged Wires

We demonstrate the guiding of a supersonic heavy-water （D2O） molecular beam using a hollow electrostatic field generated by the combination of two parallel charged-wires and two grounded metal-plates, and report some new and preliminary experimental results. In the experiment, we detect the guiding signals by using the method of time-of-flight mass spectrum and study the dependence of the relative transmission of the beam guide on the guiding voltage. Our study shows that the relative transmission of the beam guide is increased linearly with increasing guiding voltage Vguid, and the number of the guided D20 molecules is at least increased by 89.4% when the guiding voltage is ＋20.0k V. Finally, some potential applications of our guiding scheme in the molecule optics are briefly discussed.     

HIAF-BRing束团合并过程中的束流负载效应模拟

强流重离子加速器HIAF-BRing在加速完成后进行束团合并,为研究BRing中的束流负载效应对束团合并的影响,对238U35+束流进行了粒子跟踪模拟。模拟结果显示,在束团合并过程中,束流负载效应引起束团长度和束团中心位置的振荡,导致束流动量分散和束团长度的增长。束团合并过程中尾场电压以及不同束团间尾场的耦合导致的势阱畸变,是引起束团长度和束团中心振荡及束流发射度增长的原因。为了降低束流负载效应的影响,采用多谐波前馈系统进行补偿,达到了补偿束团合并过程中的束流负载效应的目的,从而确保了BRing中引出束流的品质,同时根据模拟结果确定了前馈系统需要覆盖的频率范围和需要补偿的最大尾场电压。     

Generation regimes for the runaway-electron beam in gas

The generation of the runaway-electron beam in nitrogen and helium is studied at an oscillator voltage of about 25 kV. Various regimes of the electron beam generation with a pulse duration ranging from 200 ps to several nanoseconds are realized depending on the pressure in the gas diode. An ultrashort avalanche electron beam (UAEB) with a low (10–20%) variation in the voltage across the gap is obtained at a relatively high pressure in the gas diode. The UAEB generation can be delayed relative to the leading edge of the voltage pulse by tens of nanoseconds at low oscillator voltages.     

相对论电子束在离子通道中的聚焦与输运

 基于单粒子理论,描述了相对论电子束在离子通道中的聚焦输运过程,讨论了离子-电子密度比、相对论因子、束加速电压和入射电流等系统参数对电子束的聚焦半径、纵向聚焦位置的影响。研究表明,离子通道对电子束具有强烈的聚焦效应,束流在离子通道内的传输是类周期波动传输,随传输距离增加,聚焦点处的半径逐渐增加,束流的波动幅度逐渐减小。选择适当的系统参数,可调节束聚焦点位置和聚焦点半径的大小,实现电子束的长距传输并且减少电子束的耗散。     

Analysis of superconducting cavity quench events at SSRF

Quench is important and dangerous to superconducting RF cavities. This paper illustrates the mechanism of quench and how a quench detector works, and analyzes the quench events happening during beam operations and cavity conditioning. We find that the quench protection is mostly triggered by some reasons such as fluctuation of cavity voltage, multipacting or arc, rather than a real cavity thermal breakdown. The results will be beneficial to optimize the operation parameters of superconducting cavities, to discover the real reasons for beam trip by quench interlock, and to improve the operation stability of superconducting RF systems.     

低速度零散的双阳极磁控注入电子枪设计

根据0.14 THz共焦波导回旋行波管对电子枪的要求,完成了双阳极磁控注入电子枪的设计。使用PIC软件对理论设计得到的结构参数进行了模拟优化,最终得到该枪的电子注横纵速度比为0.75,纵向速度零散1.33%。讨论了电极形状、阴极磁场、控制极电压及发射电流对电子注性能的影响,结果表明,设计过程中应对它们进行充分的优化。     

HIAF-CRing 中的俘获加速效率研究(英文)

以HIAF-CRing上典型离子238U34+为研究对象,对其纵向俘获和加速的动力学过程进行了研究。累积后的粒子能量为800 MeV/u, 经过绝热俘获和加速后,粒子被加速至1 130 MeV/u。研究结果表明,通过选择适当的俘获时间、绝热参数以及相空间面积因子等参数,应用优化后的高频俘获加速曲线,可以获得更高的俘获和加速效率。通过粒子纵向动力学追踪软件ESME 上进行模拟,得到了优化后的高频相位、高频电压曲线,使得俘获效率达到99.3%,加速效率近乎100%。同时确定出了CRing 高频腔加速U34+ 所需满足的特性参数,即电压需达到40 kV,频率范围是0:31s0:34 MHz。To reduce the beam loss during the capture and acceleration processes of CRing in HIAF project, the longitudinal beam motion is investigated using the typical ion of 238U34+during the two processes mentioned above. The ions will be captured adiabatically firstly and then will be accelerated from 800 to 1130 MeV/u with a high efficiency using optimized RF voltage and RF phase program. After that the bunched beam will be debunched for the later beam compression. Simulation of these processes by tracking appropriate distributions with the longitudinal beam dynamics code ESME has been used tofind optimum parameters such as RF phase, RF voltage. The variation of the parameter during the RF cycle and the character parameters of the RF cavity are presented.      

原子力显微镜的压电陶瓷非线性及图象畸变的校正

研制了卧式原子力显微镜(AFM)系统,讨论压电陶瓷的非线性及AFM图象畸变的软件校正方法.提出利用光束偏转法精确测定XY扫描器压电陶瓷的伸长量与控制电压之间的相互关系,得到压电陶瓷的非线性曲线;根据非线性的偏离程度,通过扫描软件对X和Y方向的扫描电压作逐点补偿,据此有效地校正图象畸变.并给出分别用未校正软件与校正软件扫描获得的部分样品的AFM图象.     

半导体的电子生伏打效应的理论

一.引言 以高速电子注射到具有阻挡层的半导体光电池上,其效果和光線相类似,使光电池的两极间产生电动势。这种效应可称为电子生伏打效应。这效应首先在1937年由Becker和Kruppke研究过,以后Ehrenberg,蓝继熹和West做了更有系统的测量。他们的测量结果表明,当电子注的能量逐渐增加时,光电池的电动势(以下简称次级电动势)最初很快地增加,达到一个极大值后又逐渐减少。相当于最大次级电动势     

Phase locking and bandwidth in a gyrotron oscillator

For imaging radar and for satelitte and space communication (e.g. NASA's deep space network), it is important that the bandwidth be as large as possible. Here we derive a formalism for computing the phase locking bandwidth that can be achieved in a gyrotron oscillator while varying the beam voltage. As an example, a second harmonic TE_02/03 gyrotron is considered. For this device, the effective bandwidth can be increased by a factor of about 3 compared with the fixed voltage case by allowing the beam voltage to change together with the input locking signal.     

双阳极磁控注入枪设计参数对其性能的影响分析

 对34GHz基波回旋管双阳极磁控注入枪的优化做了详细的研究和计算，数值模拟了阳极电压、注电流、枪体尺寸加工误差、外加直流磁场等因素对电子枪的影响。模拟结果表明：增大阳极电压不但可以提高速度比，而且可以降低横向速度零散。磁场压缩比减小，使电子注具有最小速度零散的电流值增大；同时，电子注的速度比降低，最小横向速度零散值也增大。必须慎重选择阳极形状，以提高电子枪的性能并保证电子注的稳定性；同时，还发现由于阳极结构的变化导致阴极电场分布的变化，使电子注的注电流在各因子变化过程中出现了微小的扰动。减小Bc可以增大电子注的速度比，还可以减小电子注的横向速度零散，但是当电子注的速度比增大到一定值时，电子注的性能就会变得不太稳定。     

Axial electric wake field inside the induction gap exited by the intense electron beam

While an intense electron beam passes through the accelerating gaps of a linear induction accelerator, a strong wake field will be excited. In this paper a relatively simple model is established based on the interaction between the transverse magnetic wake field and the electron beam, and the numerical calculation in succession generates a magnetic wake field distribution along the accelerator and along the beam pulse as well. The axial electric wake field is derived based on the relation between field components of a resonant mode. According to some principles in existence, the influence of this field on the high voltage properties of the induction gap is analyzed. The Dragon-I accelerator is taken as an example, and its maximum electric wake field is about 17 kV/cm, which means the effect of the wake field is noticeable.     

4 MV静电加速器调试中出现的问题及解决方案

 4 MV静电加速器由高压系统、离子源及束流系统、控制系统和气体系统四部分组成。调试中出现了离子源不起弧、加速管破裂、控制系统失灵和输电带输电能力降低等技术问题,分析了出现这些问题的原因,然后分别采取了相应的措施加以解决：变换工作流程,在每次关机前先把引出电压降为零,开机时等离子源起弧后再把引出电压升到预定值;对过渡法兰进行车加工,重新封装;对高压端的控制设备采取屏蔽措施,在输入、输出端使用TVS二极管,对控制软件进行抗干扰设计;对绝缘气体进行循环干燥等。调试出了流强为100 μA、能量在3 MeV以上的稳定质子流。     

Effect of a transverse magnetic field on the generation of electron beams in the gas-filled diode

The effect of a transverse magnetic field (0.080 and 0.016 T) on generation of an electron beam in the gas-filled diode is experimentally investigated. It is shown that, at voltage U = 25 kV across the diode and a low helium pressure (45 Torr), the transverse magnetic field influences the beam current amplitude behind a foil and its distribution over the foil cross section. At elevated pressures and under the conditions of ultrashort avalanche electron beam formation in helium, nitrogen, and air, the transverse magnetic field (0.080 and 0.016 T) has a minor effect on the amplitude and duration of the beam behind the foil. It is established that, when the voltage of the pulse generator reaches several hundreds of kilovolts, some runaway electrons (including the electrons from the discharge plasma near the cathode) are incident on the side walls of the diode.