A positive electrical potential is applied to the anode. Electron gun for brightness denki kagaku kogyo kabushiki kaisha. Field emission gun feg here electron emission is achieved in a different way than with thermionicguns. By continuing to use our website, you are agreeing to our use of cookies. A wehnelt cylinder also known as wehnelt cap, grid cap or simply wehnelt is an electrode in the electron gun assembly of some thermionic devices, used for focusing and control of the electron beam. This collection is called a space charge those electrons at the bottom of the space charge nearest to the anode can exit the gun area through the small 300 ma pulse width fwhm 15 p sec repetition rate 50 pps normalized emittance wehnelt cylinder also known as wehnelt cap, grid cap or simply wehnelt is an electrode in the electron gun assembly of some thermionic devices, used for focusing and control of the electron beam. A direct current, electrostatic thermionic electron gun is formed from several parts. Electron emitters for lithography tools katsap victor. The dirichlet problem for the cylinder the wehnelt electrode restricted by two bottoms, one of them imitates a plane cathode and another imitates the equipotential surface, was solved analytically.
Influence of cathode geometry on electron dynamics in an. What material is best for wehnelt cylinder of electron gun. As most electron guns in commercial tems and sems use autobias. It is usually a vshaped filament made of lab6 or w tungsten that is.
The established 3d models of cathode, wehnelt electrode and anode are shown in fig. Basic gun parameters for fixed gun geometry, the only mechanical variable available to the operator is the setting of the filament height within the wehnelt aperture. Laboratory for electron beam research and application, nihon university, chiba, japan abstract the electron gun wehnelt employed in the fel linac at nihon university was originally designed for extraction of the long durat ion macropulse beam with a peak current of 200 ma. Numerical simulation of beam current control mechanism in. The wehnelt electrode is held at negative potential, which defines the spatial distribution of the zerovolt equipotential and hence the size of the emitting area of the cathode. Filaments made of lab 6 generate stronger currents more electrons. By changing the d wa ratio in the gun, the size of the emitting surface and the divergence angle both change. Peak current 300 ma pulse width fwhm 15 p sec repetition rate 50 pps normalized emittance electron gun is a conventional thermionic emitter with wehnelt electrode. Inagaki, laboratory for electron beam research and application, nihon university, chiba, japan abstract the electron gun wehnelt employed in the fel linac at.
If a replaceable wehnelt aperture is fitted in the gun, then this aperture diameter may also be changed. This collection is called a space charge those electrons at the bottom of the space charge nearest to the anode can exit the gun area through the small gun. The latter electrode is at positive potential with respect to the cathode. Analytical method for electron gun calculation cambridge core. Electron sources presentation florida international university. The electron gun produces a narrowly divergent beam of electrons directed down the centerline of the column. The electron beam heating confines the cathode evaporation to the tip part and improves the working life of the cathode at higher temperatures, or emission current. The hole anode at positive bias of the high voltage of a power supply. The electron gun simulated is a directheating q60a thermionic electron gun independently developed by china aviation manufacturing technology research institute. The filament is inside the wehnelt which controls the number of electrons leaving the gun. Align the guide groove on the wehnelt with the guide pin on the electron gun and then push in the wehnelt until it clicks into position. Hi dear researchers, how important is the material of wehnelt cylinder in electron beam emitted from cathode.
Located at the top of the column where free electrons are generated by thermionic emission from a tungsten filament at 2700k. May 27, 1986 an electron gun for high brightness including a lab 6 single crystal cathode having a 100 plane on at least part of a main electron beam emission surface of a cathode tip having a top and a wehnelt having a tapered surface defining an interior angle similar to or greater than a vertical angle of said cathode tip. This file contains additional information such as exif metadata which may have been added by the digital camera, scanner, or software program used to create or digitize it. Wehnelt cylinder and the anode determines the accelerating voltage of electrons and thus their energy.
Most electron guns consist of a cathode, a wehnelt electrode, and an anode. The electric field around the filament in this case a tungsten wire, grid and anode is represented by the lines and colors look the picture below. The model of thermionic electron gun was developed. The electron gun wehnelt employed in the fel linac at nihon university was originally designed for extraction of the long duration macropulse beam with a peak current of 200 ma. Note the locking screws s, clear plastic stage p, that has been painted black in thiscase for clarity and the wehnelt cylinder aperture a. To obtain a low energy spread of the photoelectrons, tantalum emitters were used that have a work function 4. The electron flow from the gun is specified with the emission current. Electrons are primarily accelerated toward an anode that. Where do the imaging electrons in an electron microscope come from. This collection is called a space charge those electrons at the bottom of the space charge nearest to the anode can exit the gun area through the small electron gun with a telefocus wehnelt grid was rst proposed by k.
Computer simulation was conducted on electron optics of the beam formation of a point cathode electron gun. Electron gun the first and basic part of the microscopes is the source of electrons. The narrowest beamwidth observed is the minimization due to the combination of both factors. An electron gun for high brightness including a lab 6 single crystal cathode having a 100 plane on at least part of a main electron beam emission surface of a cathode tip having a top and a wehnelt having a tapered surface defining an interior angle similar to or greater than a vertical angle of said cathode tip. Design optimization of 100 kv dc gun wehnelt electrode for. The experimental characteristics reported we use cookies to enhance your experience on our website. Despite the importance of the geometries of the wehnelt electrode and the photocathode as well as the accelerator region to the overall performance of uem, surprisingly little has previously been established on what effects dominate the beam quality.
Jp2004349168a wehnelt electrode and charged particle gun. Wehnelt cylinders are found in the electron guns of cathode ray tubes and. Since 2011, the electron gun system has equipped with the high speed. What voltages are typically used in transmission electron microscopes. The focusing properties of this design are based on the shape.
The filament cathode is heated until a stream of electrons is produced. The electron gun by thermoionic electron emission the electron gun is characterized by three main parties. Pdf accurate calculations of thermionic electron gun properties. Electron microscopes utilize an electron source of some kind with the majority using a thermionic gun. A thermionic electron gun is a triode gun 3 electrode gun functions in the following manner. It is named after arthur rudolph berthold wehnelt, a german physicist, who invented it during the years 1902 and 1903. The main components of the scanning electron microscope include the electron gun, probeforming column consisting of magnetic electron lenses, apertures, and scanning coils, electron detectors, and vacuum system. Electron optics of point cathode electron gun microscopy. Emissionopticsofthesteigerwaldtypeelectrongun arxiv. Study on compact dc electron gun using single crystal cathode. A charged particle emitting member that emits charged particles, a wehnelt electrode that acts as a cathode and has an opening in the center, an anode electrode, and a dc high voltage power supply that applies a dc high voltage between the wehnelt electrode and the anode electrode and a target irradiated with the charged particle beam, and a charged particle gun including a magnetic field. The shape of the cathode surface is only approximate. Wehnelt cylinder at negative bias with respect to the filament.
Introduction the method of forming the electron beam in a new gun for rhic ebis is the same as is being used for a test ebis gun. Pdf accurate calculations of thermionic electron gun. In this gun, a straightened tungsten wire is used as the cathode, and the tip is locally heated by a diskshaped electron beam from a heater assembly set inside the wehnelt cylinder. It is usually a vshaped filament made of lab6 or w tungsten that is wreathed with wehnelt electrode wehnelt cap. Close the electron gun cap making sure that the oring is seated properly.
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