Wehnelt Research Articles

Effect of the Gap Size between the Cathode and the Wehnelt Cylinder Bore on the Emittance of the Thermionic Electron Gun

This paper includes simulating an electron gun design to investigate the effect of the distance between the cathode and the Wehnelt cylinder bore on the quality of the ion beam emittance and to obtain the best distance of that geometrical factor. A study of a group of designs was conducted to find this distance. The SIMION8.0 program has been used to calculate the trajectories of the electrons with initial kinetic energy of (0.1 eV) and electron current of (1×10-12 A). The investigation also includes comparisons between the equipotential line trajectories for each design as well as the field distribution and the electron trajectories. The best emittance distance was concluded to be (3 mm).

Simulation study for the characterization of anode shape effect on the electron beam emittance of thermionic electron gun

A systematic method had been used to develop the anode electrode shape of the thermionic electron gun by studying its effect on the emittance value, where the emittance parameter has been considered an important criterion for determining the fineness of the beam propagation. In this study, it has been found that the extended field outside the electron gun has a negative effect on the electron beam emittance parameter. A new shape of the anode has been developed and introduced in this research work to eliminate the unwanted field at the electron beam side. The cylindrical shape of the anode, which encapsulates the Wehnelt cylinder, has the effect of eliminating the adverse stray field, hence the enhancement of the beam emittance values. The new design is developed to be used in the illumination system of the electron microscopes where the highest laminar flow of the electron beam is needed.

The Relationship Between the Emitter Position and the Wehnelt Cylinder Aperture Radius of the Thermionic Electron Gun

This paper includesfinding a mathematical relationship between the distance from the emitter to the width of the Wehnelt cylinder bore and the diameter of that bore, by studying the effect and correlation of these two parameterson the quality of the electron beam. A group of electron guns with identical and variable geometric parameters were designed for the values ​​of the Wehnelt cylinder aperture radius for each case from the emitter site, which represents the distance from the emitter head to the Wehnelt cylinder aperture. As well as the calculation of the electron beam diameter and the brightness and emittance, as the mathematical relationship between these two parameters was found to be linear.

Development of the s-focus X-ray source with a long service life

The possibility of increasing the service life of the sharp-focus X-ray source of the “transmission” type is studied. Available functional analogs of this device have a short service life (about 1000 h), a relatively low focusing level at a comparable power, and a high price. An increase in the service life up to 10000 h is reached by using a cathode assembly consisting of several parallel tungsten spiral filaments with a turn diameter of ∼0.1 mm, which are placed in the Wehnelt cylinder. Electrons are accelerated to the energy required for generation of X rays from the transmission-type anode (a metal foil with a thickness of ∼100 μm) by applying a voltage of 10–40 kV between the cathode and the anode.

Electron gun with electron-beam-heated point cathode: numerical analysis of electron beam for cathode tip heating

Electron beam heating of a point cathode tip, which is utilized in a high brightness thermionic emission gun for the improvement of the cathode life at high temperatures, has been studied with numerical methods. The heating beam is provided by an annular electron gun (5 kV, ≤ 1 mA) placed inside the Wehnelt cylinder. The trajectory and broadening of some typical pencils of rays (beamlets) were made clear by tracing rays, where the electric field was computed with a surface charge method and the influence of a magnetic field in the annular gun was taken into account. The beam heated position and area of the cathode were estimated from the traced rays, and the beam current distribution was estimated by integrating the partial current distributions of many beamlets. The results show that the beam hits a wide area of the cathode tip part under practical operating conditions, and that the magnetic field has no large influence on the heating.

A self-focused multichannel electron beam source for annealing of ion-implanted semiconductors

Abstract A field emission cathode composed of multiple tungsten pins providing uniform discharge and a Wehnelt cylinder performing focusing and triggering are the new features of this pulsed electron beam source. We have successfully annealed ion-implanted CdTe, Culn S 2 and silicon from their damage states. The activation of p-type CdTe dopants can reach as high as 3 × 10 18 cm −3 .

Improving the lifetime of electron microscope pointed filaments

Single crystal pointed filaments produce a beam with high brightness and coherency — characteristics of great value in high resolution electron microscopy. However, they frequently have very short useful lifetimes due to their destruction by arcing within the gun. By improving the vacuum, reducing oil vapors and adopting a new cleaning process for gun components, these pointed filaments used with a conical Wehnelt cylinder can have a useful lifetime of 15–20 h.

A Computer Study of the Effect of Biased Wehnelt Cylinder on the Energy Distribution of Electrons

A Computer Study of the Effect of Biased Wehnelt Cylinder on the Energy Distribution of Electrons

Energy Distribution in Electron Beams

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|.

Energy Distribution of Electrons from Thermionic Cathodes with a Wehnelt Cylinder

The energy distribution in 26 keV electron beams was measured by a retarding potential analyser. Beams of small angular divergence were used to eliminate the apparent increase of energy width. The beam current was changed by varying the negative bias voltage V g at fixed cathode temperatures. For a tungsten hairpin cathode at 2620 K (Maxwellian width=0.62 eV), for example, the energy width Δ E i was 0.33 eV just above the cut-off voltage. It increased with the decrease of | V g |, reached a maximum ( Δ E i =2.3 eV) and then decreased. When the image of the cathode tip was focused on the entrance aperture of the analyser, Δ E i decreased to 1.1 eV. These results can be interpreted by the filtering effect of the bias potential and the change of the effective size of electron source which is caused by the change of the bias voltage.

A Combined Scanning Electron Microscope/Electron Microprobe Analyzer

The instrument described here is the Materials Analysis Company Model 400S combined scanning electron microscope/electron micro-probe analyzer. It was designed specifically to incorporate the most advanced features of a high performance electron microprobe analyzer with those of a medium resolution (1000A°) scanning electron microscope. The high effective x-ray take-off angle of the instrument (38.5°) offers low x-ray absorption, and thus allows the analysis of fairly rough specimens. The large depth of focus of the scanned electron images further enhances the capability of examining rough specimens.The electron-optical column comprises a triode electron gun, double condenser lens and objective lens. The electron gun uses a conventional hairpin filament, autobiased Wehnelt cylinder and anode. An externally controlled filament/Wehnelt cylinder height adjustment is provided for optimizing gun performance at all operating potentials. The double condenser lens is unitized and has two lens regions and a common energizing coil.

Performances of the Gun with a Re-entrant Shaped Wehnelt Cylinder

Performances of the Gun with a Re-entrant Shaped Wehnelt Cylinder

Time-marking a cathode-ray oscillograph by harmonics

A docile time-marker was arranged in which the oscillograph acted also as a triode giving retroaction in a tuned circuit where one of the harmonics of the trace-frequency was selected and applied to the Wehnelt cylinder so as to modulate the focus of the trace.

Investigations on Gas-Filled Cathode Ray Tubes

In considering the function of initial concentration and ray focusing it is found, for tubes using slow electrons (up to 4000 volts), that both a Wehnelt cylinder and a molecular concentrator are necessary. The action of molecular concentration has been studied thoroughly, and the static relation between pressure, beam current, and anode potentials are explained. The use of plate potentials higher than about 5000 volts was found to be unsuitable. Special phenomena accompanying such concentration are taken up, including the effect of ionic oscillations and the problem of lack of sharpness with high-frequency deflections. A remedy for the former was found in a grounded metallic outside coating, and for the latter an improvement was found by filling with light gas (hydrogen, helium). The processes in the gas space and the deflection of electrons were then investigated. The various methods for reducing secondary illumination are described. In conclusion, the reaction of the Braun tube upon the circuit was taken up and the avoidance of distortion and origin displacements by means of circuit precautions are described.

Advantages and Disadvantages of the Wehnelt Interrupter in Radiography

Advantages and Disadvantages of the Wehnelt Interrupter in Radiography

Exhibition and Description of Wehnelt's Current-Interrupter

Exhibition and Description of Wehnelt's Current-Interrupter