Current density distribution in a large cross-section beam in an electron accelerator with a multiaperture plasma cathode

An electron accelerator with a multiaperture plasma cathode with grid stabilization of the boundary of emission plasma based on a low-pressure arc discharge generating a large cross-section (750 × 150 mm²) beam with its ejection into the atmosphere or high-pressure gas through the exit foil window is described. A comparatively simple method for decreasing the nonuniformity of the current density distribution over the beam cross section using a mask with variable-diameter holes is proposed and experimentally tested. In this case, the higher the plasma concentration in the emission region, the smaller the diameter of the holes in the mask. When this mask was used, the nonuniformity of the current density distribution was decreased from ±15 and ±10% to ±10 and ±5% on the long and short sides of the beam cross section, respectively.     

Ion accelerator with space-time modulation of a relativistic electron beam

An analysis is made of a possible method of collective ion acceleration by combining spatial modulation of the electron beam potential with temporal modulation of the current. A conceptual design is proposed. Pis’ma Zh. Tekh. Fiz. 24, 74–78 (September 26, 1998)     

Point cathode electron gun using electron bombardment for cathode tip heating: numerical study of heating condition for high brightness operation

The cathode tip heating in a point cathode electron gun has been studied with numerical methods. In this gun, a straightened tungsten wire of 0.1 mm diameter is used as the cathode, and the tip part of it is locally heated by electron bombardment. The heating improves the cathode life and the gun is operated at higher cathode temperature. The gun operation requires heating conditions that confines the cathode evaporation to the tip part and keeps the temperature variation of the cathode during the evaporation small. The time variations of the temperature distribution and the cathode shape were calculated for different heating conditions. The methods and results are described, and the heating condition that is suitable for the high brightness operation of this type of gun is discussed.     

Production of the Hf isomer using a 4.5-GeV electron accelerator

High-productivity methods are required for the accumulation of long-lived isomers in amounts that are sufficient for the creation of experimental targets. A tantalum sample was activated with the Yerevan synchrotron using 4.5-GeV bremsstrahlung and the presence of ^178m2Hf was detected with good statistical accuracy by γ-activity measurements. The integrated and mean cross-section values were deduced from the experiment. The isomer-to-ground-state ratio was then estimated and compared with that known for the p+ Ta reaction studied at 660 MeV. In the present experiment, both converter and target were relatively thin for better definition of the experimental conditions. However, an assembly designed for high-productivity irradiations should be thick and then the converter can also serve as the target sample when irradiated with a high-energy electron beam. The optimization of the isomer production was solved analytically and the largest estimated yield was determined as calibrated to the experimental yield. The maximum yield of ^178m2Hf was found to be of about 3×10⁹ nuclei/s using an electron beam current of 100 μA. This is lower than the yield achieved with proton beams, although for a practical comparison the total cost and radiation safety conditions should be considered. The present results provide a basis for numerical estimations.     

医用电子直线加速器治疗计划系统参数测试研究

本文依据肿瘤放射治疗剂量学的基本理论,结合WarianClinic600医用电子直线加速器,介绍了常规放射治疗计划系统(TPS)参数如百分深度剂量、离轴比、峰值散射因子、组织—最大剂量比等基本内容的基本概念及测试方法,列举并分析了部分测试数据和曲线。分析表明测量结果与相关理论取得了令人满意的一致性。     

Radial electron density distribution in plasma flow in a coaxial hall accelerator

The values of the electron density determined from measurements of the Starr broadening of a hydrogen line are presented.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 57, No. 3, pp. 491–493, September, 1989.     

Protecting the anode foil of a high-current electron accelerator against arc-discharge damage

The mechanism of anode foil damage during the extraction of a high-power pulsed electron beam from a high-current diode has been experimentally studied on a TEU-500 electron accelerator [1]. It is established that the breakage of the anode foil is caused by the appearance of cathode spots on its surface, the intense electron emission from these spots during positive voltage pulses (postpulses following the main negative pulse of accelerating voltage), and the formation of arc discharge in the interelectrode gap. The improvement of diode matching to the pulse-forming line of the accelerator and the use of an auxiliary electrode (anode) forming additional vacuum discharge gap (crowbar) with the cathode practically excludes the anode foil breakage by arc discharge and significantly increases the working life of the foil (up to ∼10⁵ electron beam pulses).     

用于二次电子发射阴极的纳米金刚石膜

为获得导电性和二次电子发射性能均好的金刚石阴极材料,分别以CH4/Ar/H2、CH4/N2及CH4/N2/H2混合气体作为反应气源,用微波等离子化学气相沉积(MWPCVD)法制备出不同组成结构特点的纳米金刚石薄膜.XRD和Raman检测表明3种气源条件下得到的膜材均为金刚石多晶膜,但用CH4/N2反应源沉积的膜材中非金刚石相成分明显更多;AFM分析证实所有膜层的平均晶粒尺寸均在100nm以下,属纳米晶金刚石膜.用自行设计的二次电子发射系数测量装置对比检测所得膜层的二次电子发射特性,结果表明各金刚石膜均在初级入射电子能量达约1keV时,有最高的二次发射系数(δmax);并且以CH4/Ar/H2反应源制备的金刚石相纯度最高的膜材的δmax最大,达到17左右,是适用于二次电子发射阴极的潜在材料.     

Plasma microthruster based on spark discharge with a liquid metal cathode

The parameters of low-inductance vacuum spark discharge with an In-Ga liquid metal eutectic cathode have been experimentally studied. The application of a constant magnetic field of a permanent magnet significantly modifies the character of plasma flow in discharge, which ensures a significant (1.5- to 2-fold) increase in the cathodic jet impulse. The proposed discharge provides high propulsion characteristics: jet impulse per unit energy stored amounts up to about 10 (μN s)/J, which is close to the best-known values for analogous ion sources with solid metal cathodes.     

Metal-insulator cathode in an rf electron gun

The possibility of using metal-insulator cathodes in rf guns of 10 cm linear resonant electron accelerators has been studied experimentally for the first time. Results of calculations and the development of a prototype cathode are described. Results of an experimental investigation of the operating regimes of an rf gun are presented. The gun delivered a beam having a particle energy greater than 300 keV, a pulse length of 40–50 ns, and a pulsed current of 3.5–4.5 A. Pis’ma Zh. Tekh. Fiz. 24, 36–39 (October 12, 1998)     

The electron beam with virtual cathode in a two-section drift tube

An analysis based on the law of conservation of the z component of field and particle momentum in a thin annular magnetized monoenergetic electron beam in a two-section drift tube composed of tube segments with different radii (R ₁<R ₂) allowed the critical injected beam current to be determined for which a virtual cathode, formed in the wider tube at the joint section, starts traveling through the narrower tube toward the beam injection region. A region behind the traveling virtual cathode features a “squeezed” single-flux state of the beam (corresponding to the “slow” left branch of the current characteristic, high charge density, but low relativistic factor). When the injected current decreases below a critical transition level (I _in<I _Tr), the virtual cathode returns to the initial position and restores the double-flux electron beam. This current is smaller than (I _lim1+I _lim2)/2, and, depending on R ₂, varies from the limiting transport current for the narrower section (I _lim1) up to I _F/2, where I _F is the Fedosov current for this tube section.     

Stable electron emission from multipoint liquid-metal cathode

Low-frequency fluctuations of emission current from multipoint liquid-metal emitter power supplied in various regimes were studied. Images of the emitter surface before and after work were obtained. A change of the supply voltage amplitude for the transition from field emission to explosive emission regime were estimated.     

An indirectly heated solid cathode for linear electron beam emitter assembly

The paper reports design and development of an indirectly heated solid cathode for a linear electron beam emitter assembly. The solid cathode is made of a 195 mm long 8 mm wide and 2 mm thick tantalum bar with varying cross sections along its length. The emitting surface of the cathode is 110 mm in length and 4 mm in width. Thermionic electron beams emitted from a directly heated strip shaped filament have been used to heat the cathode indirectly. The temperature of the cathode, measured by a two color pyrometer, was raised to 2500 K. The innovative design of the cathode and its holding mechanism accommodates thermal expansion at high temperature, and prevents thermal deformation of the cathode. The cathode is suitable for use in strip electron beam gun and for laboratory experiments on melting and evaporation of refractory materials.     

The virtual cathode velocity during electron beam transport in a drift tube

Technical Physics Letters - A solution corresponding to a thin annular electron beam in a homogeneous drift tube featuring a uniformly moving virtual cathode (VC) has been obtained. The dependence...     

Runaway electron beam generation by a plasma cathode in atmospheric air discharge

Electron beam generation in atmospheric air discharge with a flat cathode has been experimentally studied. The discharge was excited by voltage pulses of negative polarity with an amplitude of 220 kV, a full width at half maximum of 2 ns, and a leading front width of 0.7 ns. The electron beam was monitored using luminescence of a layer of ZnS-CdS:Ag phosphor placed behind a 20-μm-thick foil anode. It was found that the intensity and homogeneity of luminescence of the phosphor layer increased when a dielectric tube with a length smaller than half of the interelectrode distance was placed in the near-cathode part of the air gap. It is concluded that a plasma cathode is formed within the volume confined by the tube and electrons emitted from this region are accelerated in the open part of the gap. In addition, the dielectric tube decreases the divergence of the electron beam.     

Photodetector performance enhancement using an electron accelerator controlled by light

A new method of photodetector performance enhancement using an embedded optical accelerator circuit within the photodetector is proposed. The principle of optical tweezer generation using a light pulse within a PANDA ring is also reviewed. By using a modified add-drop optical filter known as a PANDA microring resonator, which is embedded within the photodetector circuit, the device performance can be improved by using an electron injection technique, in which electrons can be trapped by optical tweezers generated by a PANDA ring resonator. Finally, electrons can move faster within the device via the optical waveguide without trapping center in the silicon bulk to the contact, in which the increase in photodetector current is seen. Simulation results obtained have shown that the device's light currents are increased by the order of four, and the switching time is increased by the order of five. This technique can be used for better photodetector performance and other semiconductor applications in the future.     

有机电子注入材料对Cs_2CO_3阴极结构电子注入能力的影响

系统对比了不同有机传输材料与Cs2CO3组合对阴极电子注入能力的影响。结果表明,二氮菲类衍生物与Cs2CO3组合电子注入能力最好,唑类衍生物次之,但都明显好于目前常用的Alq3材料。通过进一步比较发现,电子注入能力与有机材料的能级结构没有直接关系,这说明阴极界面处Cs2CO3与有机材料会发生不同程度的化学作用,从而改变电子注入势垒。对于金属螯合物而言,Alq3的电子注入能力明显强于Liq,说明配位金属可能参与了该作用过程。研究表明了Cs2CO3对有机材料具有较强的选择性,可以为设计合成针对Cs2CO3阴极结构的有机电子材料提供参考。     

Possibilities of production of nanopowders with high power ELV electron accelerator

Electron-beam evaporation of various natural and industrial materials in the atmosphere of different gases at atmospheric pressure can be used for the synthesis of nanosize powders. These powders are characterized by high purity and may exhibit unusual properties. In particular, nanopowders of silicon dioxide and oxide (SiO₂, SiO), magnesia (MgO), alumina (Al₂O₃), titania (TiO₂), gadolinium oxide (Gd₂O₃), various metals (tantalum, molybdenum, nickel, aluminium, copper, silver), semiconductor (Si), nitrides (AlN, TiN), and some other substances had been produced. The process of nanopowder synthesis is highly effective; in particular, the yield of oxides can exceed ten kilograms per hour.