The electron beam gun with thermionic hairpin-like cathode for welding and surface modifications

An axial thermionic electron beam emitter assembly with a special geometry of the cathode along with particular spacing of the electrodes has been used to produce a stable, sharp and high power density image at an acceleration voltage of 10 kV only. A hairpin-like tungsten wire, with diameter of 0.7 mm having semi-spherical emitting area at the crown with an angle of 45 degree at the vertex was used as a cathode. A direct heating method was used to heat the cathode. The emission current of the gun is in accordance with the Langmuir relation. An electromagnetic coil was used for focusing the beam at the target. A two dimensional programmable movement was applied to control the work site in the x-y direction. Focusing of the beam has been achieved up to 1 mm in diameter at an acceleration voltage of 10 kV.Thermionic efficiency of the gun is 4 mA W⁻¹ and the power density measured is ∼10⁵ W cm⁻².The gun was used for welding and surface modification of different materials including refractory metals.     

Numerical simulations of the thermionic electron gun for electron-beam welding and micromachining

The paper presents numerical simulations of a hairpin thermionic electron gun, an electron source for an electron-beam welding machine. New algorithm for the simulation of emission limited by space charge has been developed and implemented in the program EOD, which enables us to simulate the optical system as whole. The results of the simulation were compared with the experimental measurements.     

Effect of filament heating current on electron beam of directly heated strip-type electron gun

The method of Electron Beam-Physical Vapour Deposition (EB-PVD) for handling large substrates is well established in the metallurgical industry, where sweeping axisymmetric electron guns or multiple pencil guns are routinely used to cover a large target area. The non-uniformity in current density in those methods can be overcome, to a large extent, by using the strip-type electron gun. In this paper, we propose to use an AC-heated strip-type electron gun to cover large target areas. The magnetic field generated by the alternating filament current oscillates the beam in a direction parallel to the filament length, thereby eliminating the need for applying an external electric or magnetic field for sweeping the beam. The non-uniformity in the current density within the strip electron beam, arising due to finite length of the filament, is reduced by the use of dummy filaments on both ends of the active filament. These results are supported by electron trajectory simulations.     

Spatial distribution function for vapour flow and its validation for a two-dimensional source generated using strip electron beam

We present results on the spatial distribution of copper vapour flux in the three-dimensional flow behaviour region under identical experimental conditions as a function of the temperature of a two-dimensional (2D) evaporating source. These experimental results clearly show that, with increasing source temperature, atomic collision processes along the length and the width of a 2D source differ, which results in a differential collimation of atomic beam which can be evaluated using different beam exponents in these directions. A generalized function describing the spatial distribution of atomic vapour from a point as well as from a 2D source and deviation from Knudsen's cosine law is presented. With this distribution function, the experimentally measured vapour flux distribution from a 2D source as a function of temperature, described in terms of Knudsen numbers ranging from 1.2 to 0.23, could be fitted to an accuracy of ±5%.     

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.     

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.     

The construction of assembly and measuring devices for broadband traveling-wave tube electron injectors

The construction of electron injectors for broadband traveling-wave tubes and the effect of a spread in the geometrical dimensions of the parts of the injector on the parameters of the electron beam are considered. Equipment for the assembly and monitoring of the main dimensions of the injector and technological methods of assembly which ensure repeatability of the parameters of the traveling-wave tube and its reliability are proposed. __________ Translated from Izmeritel’naya Tekhnika, No. 12, pp. 45–48, December, 2007.     

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。     

Integrated atom density measurement in a zirconium atomic beam generated using a high-power strip electron beam source by diode laser absorption technique

Strip electron guns, capable of generating two-dimensional (length?width) evaporating sources, are used for the application of electron beam assisted physical vapour deposition to metallurgical coating of large substrates. The collisional relaxation processes in the atomic vapour generated using such a 2D-source differ significantly from those in a point source created using axisymmetric electron gun. In order to study the influence of collision processes, an atomic beam of zirconium was generated using a 130- mm-strip electron gun and its ground electronic state population was measured in a given optical path length using a tunable diode laser based on-line absorption spectroscopic technique. These measurements were carried out as a function of vertical height from the source (114 mm×6 mm) and for different source temperatures obtained by varying electron beam powers in the range of 40-91 kW.While the experimental values of integrated atom number density were observed to match very closely with those given by reported vapour flow model at low evaporating source temperatures, they showed significant deviation at high temperatures. The results are interpreted in terms of the collisional processes in the vapour stream and indicative of the fact that the vapour expansion from 2D source never runs out of collisions.