重复频率强流电子束的产生和传输实验研究

 电子束真空二极管重复频率运行时，它将表现出与单次运行时不同的特点。在电子束产生过程中，屏蔽半径应尽可能地小，且击穿延时时间较短，故选择石墨作为阴极材料。实验结果表明：在重复频率运行时，当环型阴极环厚较薄时，阴极的发射电流密度较大，因此对阴极的加热效应也加强，等离子体的膨胀速度加快，从而使得二极管阻抗减小，最后几次输出的电子束的电流较大，而电压减小；当重复频率较高时，由于加热效应使得阴极等离子体膨胀速度加快，最后几个脉冲阴极发射能力增强，波形重复性变差；当引导磁场强度增大时，阴极等离子体受到较大的磁场力约束，横向膨胀速度减慢，从而使得电子发射面积减小，总发射电流减小，二极管的阻抗增大。最后取引导磁场为1.5 T，阴极环厚为1 mm，得到重复频率100 Hz、束压827 kV、束流8.22 kA、脉冲波形之间重复性很好的均匀电子束输出。     

无箔二极管强流电子束空间密度分布初步研究

通过在强磁场条件下,利用环形刀口石墨阴极(刀口尺寸38~39mm)开展电子束轰击收集极内表面铜箔和垂直轰击金属靶片实验,对无箔二极管中电子束的空间密度分布进行了初步研究,并对其产生原因进行了分析。研究结果表明,电子束径向分布在37.2~40.2mm,存在密度较高区域(38.8~39.4mm)和密度最大值点(39.2mm),且均偏向于阴极外侧。无箔二极管环形阴极爆炸发射产生电子束的径向密度分布可用偏态分布近似。     

Perveance of a planar diode with a multipoint cathode

The I–V characteristics of a planar diode with a multipoint explosive emission cathode are studied under the conditions when the impedance of the diode is matched to the output resistance of the nanosecond generator. The experiments are carried out on the TÉU-500 (350–500 keV, 60 ns, 250 J per pulse) high-current electron accelerator. The perveances of the diodes with a spike (140 spikes) cathode, multipoint copper cathode, and cathode made of carbon felt are measured in the course of electron beam generation. Comparison is performed between the I–V characteristics of the diodes with multipoint and continuous cathodes made of the same material. It is found that the electron current of the diode is described well by Child’s law with regard to the shrinkage of the anode-cathode gap and an increase in the emissive surface due to the expanding plasma (formfactor). When the cathode is made of carbon felt or is multipoint, the space-charge-limited electron current mode sets in even 5–10 ns after the voltage is applied.     

Results of vacuum cleaning techniques on the performance of LiFfield-threshold ion sources on extraction applied-B ion diodes at 1-10TW

Uncontrolled plasma formation on electrode surfaces limits performance in a wide variety of pulsed power devices such as electron and ion diodes, transmission lines, radio frequency (RF) cavities, and microwave devices. Surface and bulk contaminants on the electrodes in vacuum dominate the composition of these plasmas, formed through processes such as stimulated and thermal desorption followed by ionization. We are applying RF discharge cleaning, anode heating, cathode cooling, and substrate surface coatings to the control of the effects of these plasmas in the particular case of applied-B ion diodes on the SABRE (1 TW) and PBFA-X (30 TW) accelerators. Evidence shows that our LiF ion source provides a 200-700 A/cm² lithium beam for 10-20 ns which is then replaced by a contaminant beam of protons and carbon. Other ion sources show similar behavior. Our electrode surface and substrate cleaning techniques reduce beam contamination, anode and cathode plasma formation, delay impedance collapse, and increase lithium energy, power, and production efficiency. Theoretical and simulation models of electron-stimulated and thermal-contaminant desorption leading to anode plasma formation show agreement with many features from experiment. Decrease of the diode electron loss by changing the shape and magnitude of the insulating magnetic field profiles increases the lithium output and changes the diode response to cleaning. We also show that the LiF films are permeable, allowing substrate contaminants to affect diode behavior. Substrate coatings of Ta and Au underneath the LiF film allow some measure of control of substrate contaminants, and provide direct evidence for thermal desorption. We have increased lithium current density by a factor of four and lithium energy by a factor of five through a combination of in situ surface and substrate cleaning, substrate coatings, and field profile modifications     

大面积均匀电子束产生实验研究

 在电子束泵浦气体激光实验中，大面积均匀电子束是获得高效能激光输出的必要条件。介绍了利用SPG-200脉冲功率源产生大面积均匀电子束的实验。SPG-200是基于SOS的全固态重复频率脉冲功率源，其开路电压大于350 kV。用于产生电子束的真空二极管阴极长294 mm，宽24 mm，两端均为半径为12 mm的半圆，栅网平面为阳极面，两者之间的距离在0~49 mm可调，阴极发射的电子束通过用于隔离激光气室和二极管真空室的压力膜及其支撑栅网引出。分别以石墨和天鹅绒为阴极材料，获得了大面积电子束输出，给出了二极管参数的测量结果，并对电子束发射均匀性进行了诊断。实验结果表明：在阴极材料为石墨、阴阳极间隙为5~9 mm时，二极管电压为240~280 kV，二极管电流为0.7~1.8 kA，输出的电子束很不均匀；在阴极材料为天鹅绒、阴阳极间隙为31~46 mm时，二极管电压为200~250 kV，二极管电流为1.5~1.7 kA，输出的电子束均匀性较好。     

强流四脉冲电子束源实验研究

 为了进行强流多电子束源研究，对现有2MeV LIA 注入器进行了四脉冲改造，二极管脉冲电压约500kV。实验研究了天鹅绒阴极在四脉冲条件下的发射能力、传导电流负载效应以及阴极等离子体运动对阴极电子发射和束能量的影响。利用空间电荷限制流模型推算出阴极等离子体膨胀速率在1 ~4cm/μs之间。     

Characteristics of electron beams formed in a diode with magnetic insulation

The problems of the formation of relativistic electron beams in a cylindrical diode with an annular cathode are discussed in the approximation of an infinitely strong guiding magnetic field. The beams are treated as infinitely thin. The following cases are investigated: 1) The formation of an electron beam moving off the cathode with an initial velocity. The case in which the field on the cathode is not equal to zero is investigated. It is shown that the potential of the electron beam can be determined in a nonunique fashion in the drift region. 2) The formation of a two-velocity electron beam. The possibility of controlling the flow of kinetic energy of the beam by varying the fraction of fast electrons in it is shown. 3) The formation of an electron beam in a diode with the help of two opposed cathodes at different potentials. A strong dependence of the current in the diode on the potential difference between the cathodes is obtained.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 36–39, December, 1981.     

猝发强流多脉冲电子束源物理设计

给出一台脉冲间隔100～1 000 ns、脉冲数2~5个、二极管电压3 MV、引出束流强度2.5 kA的猝发多脉冲电子束源的物理设计及初步调试结果。在设计中,采用感应叠加和阻抗匹配方案获得二极管高电压脉冲;试验中分别采用天鹅绒和大发射面储备式热阴极获得猝发多脉冲电子束。调试结果表明:采用大发射面热阴极可避免阴极等离子体产生,确保二极管在猝发多脉冲状态下稳定运行。初步调试获得大于2.7 MV猝发三脉冲二极管高压,并获得1.6 kA的三脉冲电子束流。     

新的高能注量电子束二极管系统

 为“闪光二号”加速器研制了新的二极管系统, 其电子束能注量比原二极管系统大3倍多。该系统由带滑闪开关的二极管、漂移管、脉冲磁场和真空靶室等部分组成, 通过减小阴极直径、增大轴向磁场强度和磁透镜比，调节滑闪开关距离和预脉冲开关气压等技术措施, 使二极管具有高能注量电子束输出的稳定工作状态, 在Marx发生器充电电压70kV条件下，在距阴极22cm的靶上获得了总能量21.5kJ、束斑直径52mm和能注量1.01kJ/cm²的电子束输出。     

合肥光源逐圈束流位置监测系统中的定时系统

定时系统是合肥光源逐圈束流位置监测和相空间测量系统中的重要组成部分，其主要目的是为数据采集卡提供与环内电子束团同步的时钟信号。该系统包含高速ECL时钟成形、分频电路、程控延时电路、控制模块等部分。可实现延时范围0～220ns，最小延时步距0.5ns，调整精度0.1ns，时钟抖动小于200ps。系统控制软件基于客户/服务器结构，操作灵活、方便。     

Specific features of explosive decomposition of pentaerythritol tetranitrate exposed to an electron beam with an explosive emission cathode

A comparative examination of the critical energy density of explosive decomposition of pentaerythritol tetranitrate exposed either to an electron beam of a GIN-600 accelerator (240 keV, 20 ns) with an explosive emission cathode or to this beam combined with metal low-temperature diode plasma has been performed. It has been demonstrated that the contribution of plasma to the development of explosive decomposition is appreciable at explosion probabilities P ≤ 0.2. At higher energy densities and explosion probabilities P ≥ 0.5, the contribution of plasma to the overall beam energy density did not exceed 10%.     

Spectra of electrons and X-ray photons in a diffusive nanosecond discharge in air under atmospheric pressure

The spectra of electrons and X-ray photons generated in nanosecond discharges in air under atmospheric pressure are investigated theoretically and experimentally. Data for the discharge formation dynamics in a nonuniform electric field are gathered. It is confirmed that voltage pulses with an amplitude of more than 100 kV and a rise time of 1 ns or less causing breakdown of an electrode gap with a small-radius cathode generate runaway electrons, which can be divided into three groups in energy (their energy varies from several kiloelectronvolts to several hundreds of kiloelectronvolts). It is also borne out that the formation of the space charge is due to electrons appearing in the gap at the cathode and a major contribution to the electron beam behind the foil comes from electrons of the second group, the maximal energy of which roughly corresponds to the voltage across the gap during electron beam generation. X-ray radiation from the gas-filled diode results from beam electron slowdown both in the anode and in the gap. It is shown that the amount of group-3 electrons with an energy above the energy gained by runaway electrons (in the absence of losses) at a maximal voltage across the gap is much smaller than the amount of group-2 electrons.     

Effect of the expanding explosive-emission centers plasma on theimpedance of a high-current diode

Formulas for the space-charge-limited electron current in a planar diode with a small hemispherical or hemi-cylindrical plasma emitter have been obtained theoretically and by a numerical simulation. For a periodic cathode structure of hemispherical emitters, an approximate expression for current is derived. Based on these results, the increase in current with time in high current explosive-emission diodes is explained. A condition has been found under which the expanding cathode plasma has no effect on the diode impedance. This is related to the electric field pressure on the cathode. A configuration of the cathode surface has been proposed which provides realization of this condition     

General scaling of pulse shortening in explosive-emission-drivenmicrowave sources

Microwave generation in devices that depend on synchronization between an electron beam and a resonant cavity or slow wave structure can be disrupted by changes in either. Explosive-emission-driven microwave sources use plasma as the electron source in the diode. This plasma is conductive enough to act as the boundary for both the applied diode voltage and the microwave electric field. The motion of this plasma can effectively change the dimensions of either the electron beam diode or the cavity and will thereby cause resonance destruction. This shortens the microwave pulse length τ_μ. A general model of the process predicts that, for a Child-Langmuir diode, microwave power falls as P∝τ_μ^-5/3 and that pulse energy falls as E∝τ_μ^-2/3. Therefore, energy efficiency declines as the pulse length is extended. We compare with data from magnetrons, MILO's and BWO's, and find that over some regions of operation the pulse length and energy from these explosive-emission-driven microwave sources agree with the plasma motion model scaling. At these applied drive voltages and output powers the microwave pulse length can be increased by finding cathode materials that generate slower plasmas     

工业X光二极管重复频率实验研究

工业X光二极管型单焦点高重复频率闪光X光机在科学研究、工业检测等领域具有重要应用前景。基于光导开关脉冲驱动源开展了金属阴极工业X光二极管重复频率运行实验, 采用烘烤处理方法研究阴极表面吸附特性对重复频率发射特性的影响;以二极管阻抗模型为理论基础, 通过重复频率实验获得的二极管电压维持时间和阻抗特性分析等离子体扩散过程。研究表明:对于高阻抗结构工业X光二极管, 金属阴极为表面吸附杂质或气体解吸附形成等离子体发射机制, 一次放电后阴极表面对气体的再吸附过程限制了其在高重复频率条件下的电流发射能力, 同时由于阴极等离子体扩散过程变慢使得二极管电压脉宽变长。具有高重复频率电流发射能力的阴极是发展单焦点重复频率X光机的基础。     

阴极区热电子发射的数值模拟

在电子束及粒子束器件中,发射系统直接影响整个器件的质量。因此,对发射系统的分析就显得非常重要。对热阴极发射的数值计算方法做了一定的探讨。对常用的平板二极管模型进行了分析,从而了解了由于这种模型而引起的计算误差。针对这些问题,采用了一些其它的处理方法来模拟热阴极的电子发射。     

Low-impedance plasma systems for generation of high-current low-energy electron beams

The results of experimental investigation and numerical modeling of the generation of low-energy (tens of keV) high-current (up to tens of kA) electron beams in a low-impedance system consisting of a plasma-filled diode with a long plasma anode, an auxiliary hot cathode, and an explosive emission cathode. The low-current low-voltage beam from the auxiliary cathode in an external longitudinal magnetic field is used to produce a long plasma anode, which is simultaneously the channel of beam transportation by residual gas ionization. The high-current electron beam is formed from the explosive emission cathode placed in the preliminarily formed plasma. Numerical modeling is performed using the KARAT PIC code.     

强流碳纳米管阴极快脉冲重频发射特性

在Cu基底上, 采用催化热解生长法制备了石墨化程度较高的碳纳米管阴极. 当电子束能量达到1 MeV、梯度约为60 kV/ns时, 发射束流强度达到15 kA, 相应密度约为1 kA/cm², 束压、束流响应快, 波形间几无延时. 以50 Hz重复频率、约15 GW束功率强流发射时, 波形稳定, 随着频率增高, 稳定性降低. 发射炮次达1000后, 表面形貌保持完整、界面无脱附; 束压与束流基本满足空间电荷限制定律, 发射机理属闪络型等离子体发射, 等离子体速度约为3.9 cm/μs.     

强流脉冲电子束二极管等离子体漂移速度的研究

 强流相对论电子束二极管阴阳极等离子体的形成和漂移,是二极管工作状态研究的重要组成部分。根据Child-Langmuir定律和二极管导流系数,结合二极管阴极电子发射面积的变化模型,给出了二极管阴阳极等离子体漂移所导致的阴阳极间隙闭合速度。     

阴阳极等离子体运动对强箍缩离子束二极管束流特性的影响

 主要研究了阴阳极等离子体运动对“闪光二号”加速器强箍缩离子束二极管束流特性的影响。给出了考虑阴阳极产生的等离子体运动对二极管间隙影响的Child-langmuir流、弱聚焦流、强聚焦流和饱和顺位流4个阶段的离子流和二极管总束流修正公式，利用这些修正公式计算的二极管总束流和离子束流强度与实测结果符合很好，在此基础上分析了提高离子束流强度和效率的方法，通过调整加速器参数，实验得到了峰值能量约500 keV，峰值电流约160 kA的高功率离子束。