Transportation of high-current electron beams in plasma and plasma-filled diodes

The results of a numerical simulation of the nonstationary processes in different charge-neutralization schemes of high-current electron beams and the results of a measurement of the beam parameters are presented. Most attention is paid to beams with a current higher than the limiting Alfven current.     

Low-energy electron beam source

Experimental results of research into a ferroelectric-plasma-source-assisted hollow anode (HA) discharge as a source of low-energy electron beams are presented. To generate electron beams, the HA auto-bias negative voltage was achieved by the discharge current flowing through the resistor connecting the HA and the grounded electrode. It is shown that this method allows reliable and reproducible generation of low-energy electron beams with electron energy of several hundreds of eV, electron current density up to several A/cm² and pulse duration of several tens of microseconds.     

10MeVLIA强流电子束的输运

介绍了１０ＭｅＶ直线感应加速器（ＬＩＡ）束输运系统布局及实验的调试规律。分析了束横向运动对束稳定输运的影响，理论分析和实验调试的结果表明，抑制束稳定输运的主要障碍来自束的横向运动。当束稳定输运时，可获得束能１０．４ＭｅＶ，束流强度２．６ｋＡ，束半高宽约１００ｎｓ的强流脉冲电子束。     

RFQ加速器同时加速同荷质比正负离子的实验研究

阐述了利用北京大学26MHz 300keV整体分离环高频四极场(ISR RFQ)加速器同时加速同荷质比正负离子的研究结果.分别用O⁺和O^－离子的连续束以及脉冲束同时注入,均实现了RFQ加速器对同荷质比正负离子的同时加速.用快靶测得的经RFQ腔同时加速后形成的O⁺及O^－离子微脉冲束与预想的正负氧离子微脉冲束相位关系完全一致.证实了同时加速时得到的氧离子束总和明显高于单加速一种离子时得到的氧离子束.在国际上首次实现了用RFQ加速器同时加速同荷质比的正负离子.     

Electron-beam instability in left-handed media

We predict that two electron beams can develop an instability when passing through a slab of left-handed media (LHM). This instability, which is inherent only for LHM, originates from the backward Cherenkov radiation and results in a self-modulation of the beams and radiation of electromagnetic waves. These waves leave the sample via the rear surface of the slab (the beam injection plane) and form two shifted bright circles centered at the beams. A simulated spectrum of radiation has well-separated lines on top of a broad continuous spectrum, which indicates dynamical chaos in the system. The radiation intensity and its spectrum can be controlled either by the beams' current or by the distance between the two beams.     

相对论速调管放大器的相位特性研究

理论分析了影响相对论速调管放大器(RKA)输出微波相位的相关因素,同时采用粒子模拟程序分析了RKA输出微波相位随电压、束流、电子束尺寸、电子束前沿和延迟时间等电子束参数以及腔体和漂移管长度等几何参数的变化,另外还开展了RKA相位特性的初步实验研究. 研究结果表明,电压、束流和电子束尺寸的改变,会造成RKA相移的改变,引导磁场、电子束前沿和延迟时间以及注入微波功率在适当范围内改变不会造成明显的RKA相移改变. RKA的相位灵敏度为2.6°,相位抖动小于20°. 关键词： 相对论速调管放大器 相位特性 功率合成 高功率微波     

On the repulsion of beam electrons

The results showing the difficulty of measurement of the current amplitude of subnanosecond electron beams are presented. It was found that the transverse velocity due to electron repulsion results in an electron fraction removal beyond a collector.     

双注磁控注入电子枪

为了增加回旋管的功率,采用双注磁控注入电子枪产生相对论电子注。与双阳极磁控注入电子枪相比,双注磁控注入电子枪产生双束电子注,在不影响电子注质量的基础上,增加电子枪的电流;电子枪产生相同电流时,双注磁控注入电子枪电子注电流小,电子注电子之间的空间电荷效应小,能够降低电子注的速度零散,提高电子注的质量。采用MAGIC软件数值模拟双注磁控注入电子枪,设计出一支大束流、低速度零散的双注磁控注入电子枪。     

低能辐照离子源设计及性能

简要介绍了低能辐照离子源的设计及性能。采用热阴极磁约束ＰＩＧ放电,并用两极多孔加减速系统引出离子束。调试结果：离子束能量在２００－２０００ｅＶ范围内可调,最大引出束流１５０ｍＡ,灯丝工作寿命１６０ｈ。     

HIAF-BRing的双向涂抹注入模拟

BRing是HIAF工程的主加速器,其设计流强为每个脉冲内的粒子数1×1011个（238U34+）,为了达到此设计流强,注入增益应达到88倍以上。BRing采用了双向涂抹注入方案,其满足BRing的注入增益要求,同时具有注入时间短和累计束分布较均匀而减小了空间电荷效应的特点。双向涂抹注入方案利用水平和垂直两组凸轨磁铁以及倾斜的静电偏转板,在水平相空间和垂直相空间内同时进行涂抹。为了检验双向涂抹注入方案能否达到BRing的设计要求,利用ORBIT程序对双向涂抹注入过程进行了模拟,模拟结果显示,在单次双向涂抹注入113圈的情况下,注入效率为97.7%,注入增益达到110.3倍,满足了BRing流强要求。累积束的分布相对均匀,空间电荷效应引起的工作点漂移约为-0.02,粒子因共振损失风险很小。针对注入束流偏角、切割板角度、工作点偏差和Bump延时等不同注入参数进行了误差分析,结果显示BRing的双向涂抹注入效率对注入参数偏差的容忍度较高。BRing is the main accelerator of High Intensity heavy Ion Accelerator Facility(HIAF) and its design current is 1×1011 particles per pulse (238U34+). To accumulate beams up to the design current, the injection gain has to reach 88. Two planes painting injection scheme is proposed for BRing. This scheme uses a tilted electrostatic septum and 8 bump magnets to paint beams into horizontal and vertical phase space simultaneously. It can inject enough beams into the ring in a short time and paint beams uniformly. The injection process is simulated using ORBIT code and 113 turns is injected into BRing with an injection efficiency of 97.7% which meets the requirement for beam current of BRing. The accumulated beams are distributed uniformly in transverse and hence have a little tune shift of -0.02 which reduces the risk of beam loss due to the resonance. Errors of injection parameters are analysed and the result shows two planes painting injection scheme has a high tolerance for errors of injection parameters.     

Detection and measurement of the current of ribbon-shaped electron beams at a particular section of a converging emitter system

A method and an associated device for directly measuring the current distribution over 28 radially converging electron beams are considered. The operation of the device, which can easily be installed in the coaxial system of a gas-discharge electron source, is described. The short-focus radial beams are found to feature a relatively high current uniformity.     

Generation of high-current relativistic electron beams with stable (for a microsecond) parameters using explosive emission cathodes

Cold explosive emission cathodes, in which a plasma serves as an emitting surface, are used to generate relativistic electron beams with a high current density in a magnetic field. The plasma parameters change within a microsecond, thereby significantly changing the geometry of the electron beam. This paper is a review of techniques for stabilizing the geometry of microsecond high-current relativistic electron beams. It is shown that only a transverse-blade explosive emission cathode in a magnetically insulated diode can generate such beams (500 keV, 3 kA) the current density profile and electron trajectory pitch factor of which remain constant for a microsecond.     

速调管输入腔开放腔的高频特性分析与实验研究

 建立了带输入波导结构的S波段速调管放大器输入腔开放腔模型,利用3维软件对其高频特性进行了数值计算研究,并对输入腔结构进行了优化设计。利用已加工的输入腔进行了高频参数的冷测实验研究,实验中的输入腔结构尺寸与高频分析中的完全相同,实验结果与高频分析结果一致。用3维PIC程序对电子束经过该输入腔后的束流调制以及注入微波的吸收情况进行了模拟。模拟结果表明：该输入腔与微波注入波导匹配很好,注入微波能被电子束和谐振腔全部吸收,在输入腔间隙后37 cm处得到了13%的基波电流调制深度。     

S波段多注相对论速调管的小信号理论

多注相对论速调管利用多注电子注并行工作,各电子注在传输过程中彼此独立,利于提高注波互作用效率,抑制杂模振荡。分析多注相对论速调管的小信号理论,从谐振腔内电场的场形函数出发确定了不同腔体结构的耦合系数的计算方法,得到了不同电子注形状、注数时的基波电流分量轴向变化过程,并进行模拟验证。结果表明:同轴谐振腔的间隙耦合系数要大于圆柱腔的间隙耦合系数,采用同轴谐振腔更有利于注波互作用;电子群聚过程与每注电子注的势能密切相关,提高电子注数目有助于得到更大的基波电流分量。在电子注电压600 kV、电流5 kA、间隙电压30 kV的条件下,输入腔后的基波电流分量达800 A。     

Preparation of graphene on SiC by laser-accelerated pulsed ion beams

Laser-accelerated ion beams (LIBs) have been increasingly applied in the field of material irradiation in recent years due to the unique properties of ultra-short beam duration, extremely high beam current, etc. Here we explore an application of using laser-accelerated ion beams to prepare graphene. The pulsed LIBs produced a great instantaneous beam current and thermal effect on the SiC samples with a shooting frequency of 1 Hz. In the experiment, we controlled the deposition dose by adjusting the number of shootings and the irradiating current by adjusting the distance between the sample and the ion source. During annealing at 1100 ℃, we found that the 190 shots ion beams allowed more carbon atoms to self-assemble into graphene than the 10 shots case. By comparing with the controlled experiment based on ion beams from a traditional ion accelerator, we found that the laser-accelerated ion beams could cause greater damage in a very short time. Significant thermal effect was induced when the irradiation distance was reduced to less than 1 cm, which could make partial SiC self-annealing to prepare graphene dots directly. The special effects of LIBs indicate their vital role to change the structure of the irradiation sample.     

Numerical Analysis of Weakly Relativistic Large Orbit Gyrotron with Permanent Magnet System

High-harmonic gyro-devices with axis-encircling electron beams known as large orbit gyrotrons (LOG) represent an appealing alternative to the conventional gyrotrons. In this paper we investigate the feasibility of such device operating with low current and low energy electron beams formed by a novel electron gun with a permanent magnet system. The results from the numerical experiments indicate the possibility to excite TE₄₁ mode at fourth harmonic of the cyclotron frequency. Simulations predict generation of microwave radiation with frequency 104 GHz and output power near 1 kW.     

Runaway electrons and Generation of high-power subnanosecond electron beams in dense gases

Works on the physics of electron runaway in gases, developing a new understanding of formation of runaway electron beams in gas discharge, are reviewed. Results of experiments with atmospheric-pressure gas-filled diodes, in which subnanosecond electron beams with a record current amplitude were obtained, are reported. The properties of volume nanosecond discharge, allowing to obtain such beams, are analyzed.     

Afterglow工作模式下ECR离子源脉冲束的产生

为满足国家大科学工程兰州重离子冷却储存环的要求,在14.5GHz ECR 离子源上进行afterglow工作模式的实验,首次产生了高电荷态脉冲束流Ar¹¹⁺和Ar¹²⁺,给出了初步实验结果,并对结果进行了分析和解释.     

S波段相对论速调管放大器同轴输出腔的数值模拟

 介绍了S波段强流相对论速调管放大器（RKA）同轴输出腔内束波转换效率和腔主要参数的计算、微波提取的粒子模拟和优化以及实验。模拟计算时,采用单间隙的同轴输出腔,束压580 kV、束流4 kA的环行电子束,基波调制深度为80%,利用3维粒子程序得到约500 MW的微波输出功率,效率21.5%。将该模拟结果应用于实验的设计,实验中采用束压550 kV、束流4 kA的电子束得到功率500 MW、脉宽120 ns的输出微波,束波转换效率22.7%,实验结果与模拟结果吻合较好。     

Generation of a high-current beam of multiply charged ions from a dense plasma produced by high-power millimeter-wave gyrotron radiation under ECR conditions

Experimental data for generating intense beams of multiply charged heavy gas ions are reported. The beams are extracted from the dense plasma of an ECR discharge with quasi-gasdynamic confinement provided by the powerful microwave radiation of a gyrotron in a magnetic trap. The axisymmetric magnetic trap makes it possible to extract uniform (in transverse coordinates) plasma fluxes from it, and the use of a multiple-aperture extraction system makes it possible to increase the beam current by more than an order of magnitude compared with the ECP sources currently available. Multiply charged nitrogen ion beams with a current of 150 mA and a normalized emittance of 0.9π mm mrad are obtained.