Point-Cathode Electron Gun Using Electron-Beam Bombardment for Cathode Tip Heating

1990 ◽  
Vol 48 (1) ◽  
pp. 198-199
Author(s):  
Ryo Iiyoshi ◽  
Susumu Maruse ◽  
Hideo Takematsu
Keyword(s):  
Electron Beam ◽  
Tungsten Wire ◽  
Local Heating ◽  
Electron Gun ◽  
Original Position ◽  
Beam Power ◽  
Radius Of Curvature ◽  
High Brightness ◽  
Beam Focusing ◽  
Time Operation

Point cathode electron gun with high brightness and long cathode life has been developed. In this gun, a straightened tungsten wire is used as the point cathode, and the tip is locally heated to higher temperatures by electron beam bombardment. The high brightness operation and some findings on the local heating are presented.Gun construction is shown in Fig.l. Small heater assembly (annular electron gun: 5 keV, 1 mA) is set inside the Wehnelt electrode. The heater provides a disk-shaped bombarding electron beam focusing onto the cathode tip. The cathode is the tungsten wire of 0.1 mm in diameter. The tip temperature is raised to the melting point (3,650 K) at the beam power of 5 W, without any serious problem of secondary electrons for the gun operation. Figure 2 shows the cathode after a long time operation at high temperatures, or high brightnesses. Evaporation occurs at the tip, and the tip part retains a conical shape. The cathode can be used for a long period of time. The tip apex keeps the radius of curvature of 0.4 μm at 3,000 K and 0.3 μm at 3,200 K. The gun provides the stable beam up to the brightness of 6.4×106 A/cm2sr (3,150 K) at the accelerating voltage of 50 kV. At 3.4×l06 A/cm2sr (3,040 K), the tip recedes at a slow rate (26 μm/h), so that the effect can be offset by adjusting the Wehnelt bias voltage. The tip temperature is decreased as the tip moves out from the original position, but it can be kept at constant by increasing the bombarding beam power. This way of operation is possible for 10 h. A stepwise movement of the cathode is enough for the subsequent operation. Higher brightness operations with the rapid receding rates of the tip may be improved by a continuous movement of the wire cathode during the operations. Figure 3 shows the relation between the beam brightness, the tip receding rate by evaporation (αis the half-angle of the tip cone), and the cathode life per unit length, as a function of the cathode temperature. The working life of the point cathode is greatly improved by the local heating.

LASER BEAT-WAVE BUNCHED BEAM FOR COMPACT SUPERRADIANCE SOURCES

2007 ◽  
Vol 21 (03n04) ◽  
pp. 287-299 ◽  
Author(s):  
YEN-CHIEH HUANG
Keyword(s):  
Computer Simulation ◽  
Electron Beam ◽  
Electron Beams ◽  
Beat Frequency ◽  
Laser System ◽  
Electron Gun ◽  
High Brightness ◽  
Wave Laser

A periodically bunched electron beam is useful for generating high-brightness electron superradiance. This paper studies the generation and acceleration of density-modulated electron beams from a photocathode electron gun driven by a laser beat wave. Computer simulation shows the feasibility of accelerating and preserving the density-modulated electron beam in an accelerator. This paper also details the implementation of a beat-wave laser system with a variable beat frequency for driving a photocathode electron gun.

scholarly journals Research and development of an electron beam focusing system for a high-brightness X-ray generator

2010 ◽  
Vol 18 (1) ◽  
pp. 53-57 ◽  
Author(s):  
Takeshi Sakai ◽  
Satoshi Ohsawa ◽  
Noriyoshi Sakabe ◽  
Takashi Sugimura ◽  
Mitsuo Ikeda
Keyword(s):  
Electron Beam ◽  
Research And Development ◽  
High Brightness ◽  
X Ray ◽  
Beam Focusing

Three-Dimensional Electron-Beam Deflection and Missed Joint in Welding Dissimilar Metals

1997 ◽  
Vol 119 (4) ◽  
pp. 832-839 ◽  
Author(s):  
P. S. Wei ◽  
F. K. Chung
Keyword(s):  
Electron Beam ◽  
Electrical Contact ◽  
Three Dimensional ◽  
Electron Gun ◽  
Beam Deflection ◽  
Beam Power ◽  
Dissimilar Metals ◽  
Electrical Contact Resistance ◽  
Paraboloid Of Revolution

Three-dimensional deflection of the electron beam resulting in a missed joint due to thermoelectric magnetism generated while welding dissimilar metals is systematically investigated. The incident energy rate distribution is assumed to be Gaussian and the deep and narrow welding cavity induced is idealized as a paraboloid of revolution. With a three-dimensional analytical solution for the temperature and by solving Maxwell’s electromagnetic equations, thermoelectric currents, magnetic flux densities, and deflections of the beam are found. The predictions agree with available experimental data. The results find that missed joints can be reduced by increasing the dimensionless accelerating voltage-to-Seebeck e.m.f. parameter, Peclet number, and effective electrical contact resistance parameter, and decreasing dimensionless beam power, magnetic permeabilities, and electrical conductivity ratio between metals 1 and 2. Tilting workpieces and shifting the electron gun from the joint line are also feasible. A three-dimensional analysis is required for a successful determination of beam deflection.

Optimization of LaB6 Cathode Tip Shape for Maximum Brightness Over Lifetime

1990 ◽  
Vol 48 (1) ◽  
pp. 430-431
Author(s):  
Locke Christman
Keyword(s):  
Electron Microscopy ◽  
Electron Beam ◽  
Cone Angle ◽  
Small Diameter ◽  
Electron Gun ◽  
Small Radius ◽  
Geometrical Parameters ◽  
High Brightness ◽  
High Level ◽  
Tip Radius

LaB6 cathodes are widely used as high brightness cathodes in electron microscopy and are capable of providing about five times the brightness of a tungsten hairpin filament. It is desirable to optimize the shape of the LaB6 tip to provide the highest possible brightness and to insure that this high level of brightness is maintained over the life of the cathode.It is well known that a high brightness electron beam is important in obtaining ultimate resolution in electron microscopy. Brightness is defined as the current density per unit solid angle, or amperes per square centimeter per steradian, in the electron beam. In electron microscopy, one would like to obtain the maximum possible brightness for the particular electron gun. Brightness is a conserved quantity, meaning that as the beam traverses the column, brightness can not be gained, only lost. Therefore, one must begin with the brightest possible cathode in order to obtain the best possible electron beam brightness.Much work has been done to determine the optimum LaB6 cathode tip shape and crystallographic orientation which will provide the highest brightness over cathode lifetime. The purpose of this is to review some of the previous results, present further data, and draw conclusions as to the optimum LaB6 cathode tip shape for high sustained brightness over cathode life. Nearly all commercially available LaB6 cathodes for electron microscopy employ an axially oriented LaB6 <100> crystal with a conical tip. Most are made with a full cone angle of 2α=90° (Figure 1). Some have a small radius, hemispherical point at the apex of the cone, while others simply have a small diameter truncation (flat) on top of the cone. The geometrical parameters affecting cathode brightness which will be considered here are hemispherical tip radius (R) and flat diameter (ϕ). Of primary interest is the dependence of brightness over lifetime with the variation of these parameters, and the comparison between the hemispherical and the flat tips.

A Process Model for Electron Beam Welding with Variable Thickness

2013 ◽  
Vol 762 ◽  
pp. 538-543
Author(s):  
Jiang Lin Huang ◽  
Jean Christophe Gebelin ◽  
Richard Turner ◽  
Roger C. Reed
Keyword(s):  
Electron Beam ◽  
Variable Thickness ◽  
Process Model ◽  
Electron Beam Welding ◽  
Welding Process ◽  
Beam Power ◽  
Welding Parameters ◽  
Eb Welding ◽  
Experimental Calibration ◽  
Beam Focusing

A process model for electron beam (EB) welding with a variable thickness weld joint has been developed. Based on theoretical aspects and experimental calibration of electron beam focusing, welding parameters including beam power, focus current, working distance and welding speed were formulated in the heat source model. The model has been applied for the simulation of assembly of components in a gas turbine engine compressor. A series of metallographic weld sections with different welding thickness were investigated to validate the predicted thermal results. The workpieces were scanned both prior to-and after welding, using automated optical metrology (GOM scanning) in order to measure the distortion induced in the welding process. The measured result was compared with predicted displacement. This work demonstrates the attempts to improve the EB welding process modelling by connecting the heat input directly from the actual welding parameters, which could potentially reduce (or even remove) the need for weld bead calibrations from experimental observation.

New type electron gun with electrostatic and electromagnetic lenses

1978 ◽  
Vol 36 (1) ◽  
pp. 62-63
Author(s):  
T. Ichinokawa ◽  
H. Maeda
Keyword(s):  
Electron Microscopy ◽  
Electron Beam ◽  
Optimum Condition ◽  
Bias Voltage ◽  
Electron Gun ◽  
Charge Effect ◽  
Micro Fabrication ◽  
Maximum Brightness ◽  
New Type ◽  
The Ideal

I. IntroductionThermionic electron gun with the Wehnelt grid is popularly used in the electron microscopy and electron beam micro-fabrication. It is well known that this gun could get the ideal brightness caluculated from the Lengumier and Richardson equations under the optimum condition. However, the design and ajustment to the optimum condition is not so easy. The gun has following properties with respect to the Wehnelt bias; (1) The maximum brightness is got only in the optimum bias. (2) In the larger bias than the optimum, the brightness decreases with increasing the bias voltage on account of the space charge effect. (3) In the smaller bias than the optimum, the brightness decreases with bias voltage on account of spreading of the cross over spot due to the aberrations of the electrostatic immersion lens.In the present experiment, a new type electron gun with the electrostatic and electromagnetic lens is designed, and its properties are examined experimentally.

Energy Distribution in Electron Beams

1972 ◽  
Vol 30 ◽  
pp. 568-569
Author(s):  
Tamotsu Ohno
Keyword(s):  
Electron Beam ◽  
Energy Distribution ◽  
Cross Section ◽  
Integral Curve ◽  
Electron Beams ◽  
Electron Gun ◽  
Angular Divergence ◽  
Apparent Increase ◽  
Integral Width ◽  
The Cross

The energy distribution in an electron; beam from an electron gun provided with a biased Wehnelt cylinder was measured by a retarding potential analyser. All the measurements were carried out with a beam of small angular divergence (<3xl0-4 rad) to eliminate the apparent increase of energy width as pointed out by Ichinokawa.The cross section of the beam from a gun with a tungsten hairpin cathode varies as shown in Fig.1a with the bias voltage Vg. The central part of the beam was analysed. An example of the integral curve as well as the energy spectrum is shown in Fig.2. The integral width of the spectrum ΔEi varies with Vg as shown in Fig.1b The width ΔEi is smaller than the Maxwellian width near the cut-off. As |Vg| is decreased, ΔEi increases beyond the Maxwellian width, reaches a maximum and then decreases. Note that the cross section of the beam enlarges with decreasing |Vg|.

A New High Intensity Grid Cap for RCA-EMU-3 Electron Microscopes

1968 ◽  
Vol 26 ◽  
pp. 316-317
Author(s):  
George Christov ◽  
Bolivar J. Lloyd
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
High Voltage ◽  
High Intensity ◽  
Electron Gun ◽  
Tungsten Filament ◽  
Fluorescent Screen ◽  
Electron Microscopes ◽  
Pass Through ◽  
Ground Potential

A new high intensity grid cap has been designed for the RCA-EMU-3 electron microscope. Various parameters of the new grid cap were investigated to determine its characteristics. The increase in illumination produced provides ease of focusing on the fluorescent screen at magnifications from 1500 to 50,000 times using an accelerating voltage of 50 KV.The EMU-3 type electron gun assembly consists of a V-shaped tungsten filament for a cathode with a thin metal threaded cathode shield and an anode with a central aperture to permit the beam to course the length of the column. The cathode shield is negatively biased at a potential of several hundred volts with respect to the filament. The electron beam is formed by electrons emitted from the tip of the filament which pass through an aperture of 0.1 inch diameter in the cap and then it is accelerated by the negative high voltage through a 0.625 inch diameter aperture in the anode which is at ground potential.

Performance and applications of the holography electron microscope

1993 ◽  
Vol 51 ◽  
pp. 1078-1079
Author(s):  
Akira Tonomura
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Phase Measurement ◽  
Electron Holography ◽  
Imaging Method ◽  
High Contrast ◽  
Magnetic Lens ◽  
High Brightness ◽  
Holographic Imaging ◽  
Dynamic Observation

Electron holography is a two-step imaging method. However, the ultimate performance of holographic imaging is mainly determined by the brightness of the electron beam used in the hologram-formation process. In our 350kV holography electron microscope (see Fig. 1), the decrease in the inherently high brightness of field-emitted electrons is minimized by superposing a magnetic lens in the gun, for a resulting value of 2 × 109 A/cm2 sr. This high brightness has lead to the following distinguished features. The minimum spacing (d) of carrier fringes is d = 0.09 Å, thus allowing a reconstructed image with a resolution, at least in principle, as high as 3d=0.3 Å. The precision in phase measurement can be as high as 2π/100, since the position of fringes can be known precisely from a high-contrast hologram formed under highly collimated illumination. Dynamic observation becomes possible because the current density is high.

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