Performance Of Electron Gun Research Articles

Performance optimization of indirectly heated cathode based electron gun by controlling high voltage surface flashover and beam positioning at target plane

In this paper, an improved design of a practical 2700-bent, 60 kV, 60 kW, indirectly heated cathode-based electron gun has been proposed in order to reduce high voltage breakdown in the electron gun. This ensures reliable and uninterrupted operation of the electron gun for melting and evaporation applications. For this purpose, 1) shield electrodes have been optimally designed for gun insulators in order to provide desired voltage grading/shielding and 2) optimization of positioning of the gun electrodes and optimal current in Helmholtz coil in order to ensure desired 2700-bent electron beam at the target plane, have been achieved. A new optimization technique incorporating formulation of a 3-D cost function is developed and is implemented by using an open-source web application utilizing python script. Electrostatic and electromagnetic 3-D gun simulations are carried out by using CST Studio Particle Tracking Module with modified parameters. Trial experiments have been conducted to monitor breakdown signal which showed improvement in surface flashover performance of electron gun. Molybdenum tablets were successfully melted at target plane by achieving the desired 2700-bent electron beam. Dimensions of molybdenum melt pool and simulation results showed good correspondence.

Study of a Novel Bidirectional Compression Electron Gun for $W$ -Band Sheet Beam TWT

A novel bidirectional compression electron gun is designed for a W-band sheet beam traveling-wave tube. A parabolic curved cathode and a beam focusing electrode based on spline interpolation curves are proposed to obtain a beam with good quality. Two directional compressions are introduced to reduce the beam loading of cathode. A 30-kV, 0.97-A beam is emitted by a curved 0.112-cm2 cathode with a beam loading of 8.66 A/cm2. The beam at waist position is 1.4 mm $\times0.4$ mm with a compression ratio of 2 and 10 in two directions separately. Studies of beam emittance and sensitivity of beam dynamics to mechanical errors are also carried out to understand the influence of structure parameters on electron gun performance.

WE‐G‐BRD‐09: Novel MRI Compatible Electron Accelerator for MRI‐Linac Radiotherapy

Purpose:MRI guided radiotherapy is a rapidly growing field; however current linacs are not designed to operate in MRI fringe fields. As such, current MRI‐ Linac systems require magnetic shielding, impairing MR image quality and system flexibility. Here, we present a bespoke electron accelerator concept with robust operation in in‐line magnetic fields.Methods:For in‐line MRI‐Linac systems, electron gun performance is the major constraint on accelerator performance. To overcome this, we propose placing a cathode directly within the first accelerating cavity. Such a configuration is used extensively in high energy particle physics, but not previously for radiotherapy. Benchmarked computational modelling (CST, Darmstadt, Germany) was employed to design and assess a 5.5 cell side coupled accelerator with a temperature limited thermionic cathode in the first accelerating cell. This simulation was coupled to magnetic fields from a 1T MRI model to assess robustness in magnetic fields for Source to Isocenter Distance between 1 and 2 meters. Performance was compared to a conventional electron gun based system in the same magnetic field.Results:A temperature limited cathode (work function 1.8eV, temperature 1245K, emission constant 60A/K/cm2) will emit a mean current density of 24mA/mm2 (Richardson's Law). We modeled a circular cathode with radius 2mm and mean current 300mA. Capture efficiency of the device was 43%, resulting in target current of 130 mA. The electron beam had a FWHM of 0.2mm, and mean energy of 5.9MeV (interquartile spread of 0.1MeV). Such an electron beam is suitable for radiotherapy, comparing favourably to conventional systems. This model was robust to operation the MRI fringe field, with a maximum current loss of 6% compared to 85% for the conventional system.Conclusion:The bespoke electron accelerator is robust to operation in in‐line magnetic fields. This will enable MRI‐Linacs with no accelerator magnetic shielding, and minimise painstaking optimisation of the MRI fringe field.This work was supported by US (NIH) and Australian (NHMRC & Cancer Institute NSW) government research funding. In addition, I would like to thank cancer institute NSW and the Ingham Institute for scholarship support.

Performance of an electron gun for a high-brightness X-ray generator

A prototype thermionic electron gun for a high-brightness X-ray generator has been developed. Its extraction voltage and design current are 60 kV and 100 mA (DC), respectively. The X-ray generator aims towards a maximum brilliance of 60 kW mm(-2). The beam sizes at the rotating anticathode must therefore be within 1.0 mm x 0.1 mm and a small beam emittance is required. The fabricated electron gun optimizes an aperture grid and a Whenelt electrode. The performance of the prototype electron gun measured using pulsed-beam tests is as follows: maximum beam current, 85.7 mA; beam focus size at the rotating anticathode, 0.79 mm x 0.13 mm. In DC beam tests, FWHM beam sizes were measured to be 0.65 mm x 0.08 mm at the rotating anticathode with a beam current of 45 mA. The beam current recently reached approximately 60 mA with some thermal problems.

Nanotip electron gun for the scanning electron microscope

Experimental nanotips have shown significant improvement in the resolution performance of a cold field emission scanning electron microscope (SEM). Nanotip electron sources are very sharp electron emitter tips used as a replacement for the conventional tungsten field emission (FE) electron sources. Nanotips offer higher brightness and smaller electron source size. An electron microscope equipped with a nanotip electron gun can provide images with higher spatial resolution and with better signal-to-noise ratio. This could present a considerable advantage over the current SEM electron gun technology if the tips are sufficiently long-lasting and stable for practical use. In this study, an older field-emission critical dimension (CD) SEM was used as an experimental test platform. Substitution of tungsten nanotips for the regular cathodes required modification of the electron gun circuitry and preparation of nanotips that properly fit the electron gun assembly. In addition, this work contains the results of the modeling and theoretical calculation of the electron gun performance for regular and nanotips, the preparation of the SEM including the design and assembly of a measuring system for essential instrument parameters, design and modification of the electron gun control electronics, development of a procedure for tip exchange, and tests of regular emitter, sharp emitter and nanotips. Nanotip fabrication and characterization procedures were also developed. Using a "sharp" tip as an intermediate to the nanotip clearly demonstrated an improvement in the performance of the test SEM. This and the results of the theoretical assessment gave support for the installation of the nanotips as the next step and pointed to potentially even better performance. Images taken with experimental nanotips showed a minimum two-fold improvement in resolution performance than the specification of the test SEM. The stability of the nanotip electron gun was excellent; the tip stayed useful for high-resolution imaging for several hours during many days of tests. The tip lifetime was found to be several months in light use. This paper summarizes the current state of the work and points to future possibilities that will open when electron guns can be designed to take full advantage of the nanotip electron emitters.

Development of a 1-MV Field-Emission Electron Microscope III. Electron Optical Design and Development of Field-Emission Electron Gun

Abstract Bright and coherent electron beams have been opening new frontiers in science and technology. So far, we have developed several field-emission transmission electron microscopes (FE-TEM) with increasing accelerating voltages to provide higher beam brightness. By using a 200-kV FE-TEM and electron holography techniques, we directly confirmed the Aharonov-Bohm effect. A 350-kV FE-TEM equipped with a low-temperature specimen stage enabled us to observe moving vortices in superconductors.2 Most Recently, we have developed a new 1-MV FE-TEM with a newly designed FE gun to obtain an even brighter and more coherent electron beam. Electron beam brightness, Br, defined in Figure 1, is suitable for measuring the performance of electron guns, since both lens aberrations and mechanical/electrical vibrations contribute to a decrease in beam brightness, and beam coherency is proportional to (Br)1/2. Therefore, we optimized design of the illuminating system and its operation by maximizing the electron beam brightness.

Electron‐impact excitation and emission cross sections of the H2 Lyman and Werner Systems

Excitation functions of the H2 Lyman (Ly) ( B1∑∑u ‐ X1∑∑g) and Werner (W) (C1∏u ‐ X1∑∑g ) band systems have been reanalyzed using a combination of measurements and theoretical considerations. These systems are prominent emitters in outer planet atmospheric dayglow and auroral activity and can be used to infer energy deposition and heating rates. Earlier measurements of the cross sections reported by Shemansky et al. [1985a] have been found to be inaccurate in the threshold energy region. A combination of high‐resolution spectral and shape function measurements obtained at the Jet Propulsion Laboratory (JPL) in low‐ and medium‐energy regions have been used to obtain relative excitation shape functions of the two systems. At energies above 250 eV, we have used the measurements obtained earlier by De Heer and Carrière [1971] in order to define the first two terms of the Born electric dipole collision strength. The complete set of collision strength terms is obtained by combining the JPL and De Heer and Carrière [1971] data. We have found that, contrary to results of Shemansky et al. [1985a], the shape functions of the H2 Ly and W systems, expressed in units of threshold energy, are the same within experimental error. Absolute cross sections of the H2 Ly and W systems are established using the theoretical oscillator strengths of Abgrall et al. [1987, 1993a, b, c] and Abgrall and Roueff [1989]. The atomic hydrogen H Ly α emission cross section resulting from dissociative excitation of H2 at 100 eV obtained from relative intensities of H2 W emission lines is also derived and compared with other experimental measurements. At a gas temperature of 300 K and electron energy of 100 eV, the cross sections for the H Ly α, H2 Ly, and W emissions are (0.716 ± 0.095) × 10−17, (2.62 ± 0.34) × 10−17, and (2.41 ± 0.31) × 10−17 cm2, respectively. The accuracy of the absolute values and shape functions is limited primarily by electron gun performance, as was the case for Shemansky et al. The rotational dependence of the transition dipole matrix elements and perturbations between the B 1∑+u and C1∏+u states have a significant effect on the cross sections.

Automatic Electron Beam Diagnostics using an Electron Beam Analyzer

Electron gun is one of the most critical sub-systems of a microwave tube. The performance of electron gun has a profound effect on the overall tube characteristics. Design and fabrication of the electron gun is quite involved and complex. Advanced computer aided design and simulation techniques have been developed for gun design. However, the measurement of physical characteristics of the election gun is vital and has the final say in gun design validation and performance evaluation. Before using an electron gun fabricated as per computer aided design and simulation in a microwave tube, it is necessary to practically evaluate the characteristics of the beam produced by the electron gun. Modifications, if necessary, can be incorporated in the design in order to achieve the desired performance of the gun. With this objective, an electron beam analyzer (EBA) system was designed and developed indigenously at MTRDC, Bangalore. This system is capable of analyzing various properties of the electron beam formed by an electron gun. This paper describes the salient features and capabilities of the EBA system and presents the computer aided automatic test results which include 3-D current distribution plot and contour map.

The dependence of electron gun performance on filament material

A comparison of thoriated iridium, thoriated tungsten and tungsten filaments in a low energy, high resolution electron gun is investigated by the direct measurement of an atomic excitation cross section.

Electron Optics for CRT's: Computer Modeling

The performance of electron guns can be improved with the aid of accurate visual models of the gun and beam, including thermal spreading and space charge effects, as previously described in the literature. To effectively model a CRT-type of electron gun, a scaled approach is outlined in which the region of the cathode and control grid is treated with greater accuracy than are the succeeding regions of the lens and field-free space. Using computer-drawn plots of the gun structure, field, and beam, the five steps needed to imploment this scaled approach are summarized.

The.assessment of relative electron gun performance The assessment of relative electron gun performance Comments on the paper entitled “ Digital computer studies of electron guns for electron microscopes “†

Abstract A method of comparing the basic performance of electron guns is described. The method is applied to some recently computed results on two versions of an electron gun which has a hairpin-filament cathode.

Gridded electron guns for high average power

The design and performance of electron guns producing high-average-power beams which are controlled by an intercepting-type grid are described. The design consists of a modification of the design of Pierce-type electron guns to allow for the effect of grid insertion, and calculation of the amplification factors based on the potential distribution. The performance is evaluated in terms of the beam shapes and average beam powers obtainable. Measured amplification factors are compared with calculated values. Factors influencing the measured beam shapes are discussed. Trajectories of electrons emitted as secondaries from the grid and those of electrons deflected by the lens effect of the grid wires were plotted using an analog computer and electrolytic tank. The shapes and focusing properties of electron beams from similar gridded and nongridded guns are compared. Expressions relating the average beam power capability to the gun and grid dimensions are developed. The calculated average beam power capabilities are compared with measured values. Average beam power as high as 8 kw has been obtained with electron guns of a size suitable for use in X-band twt's.

Simple Methods for preparing Pointed Filaments for the Electron Microscope

THE performance of electron guns used in the electron microscope has been studied by Haine and Einstein1, Boersch and Born2, and others. The present indications are that pointed filaments improve this performance. The first of these filaments was prepared by Hibi3 by hand-polishing or etching a short length of tungsten wire which was welded or otherwise attached to a conventional hairpin filament according to Muller's method4. Heating was obtained by conduction from the hairpin.

The ultimate performance of the single-trace high-speed oscillograph

The limitations to writing speed and deflection sensitivity of the single-trace high-speed oscillograph are analysed in terms of theoretical electron-gun performance and the spherical aberration of practical electron lenses. It is shown that considerable improvements over the best present-day designs are theoretically possible. The results indicate the design trends which should achieve the improved performance.

Factors Governing Performance of Electron Guns in Television Cathode-Ray Tubes

On the basis of Langmuir's limiting-current-density relationship, it is shown that the useful beam current in a conventional television cathode-ray tube has an upper limit defined by e A2 I.= 1.13 ioE2-- tan2o where I<L>s</L> = the beam current; i<L>0</L> = the cathode-current density; E<L>2</L> = the second-anode voltage relative to the cathode; e = the electron charge; k = Boltzmann's constant; T = the absolute temperature of the cathode; A = the aperture of the final focusing system; N = the number of scanning lines; and, ϕ = the equivalent deflection angle. This result is derived for the case of an ideal electron gun with no defining apertures. In practice this upper limit of beam current is not attained because of aberrations and space-charge mutual repulsion effects.