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Electron Guns are considered as important and useful devices in electron scattering studies. So far, different models of these guns have been designed. In this paper, using the computational code SIMION- 8.0 3D we simulate a low energy electron gun which is appropriate for the electron collision process. This computational code may be used to correct the canonical properties of electrostatic lenses and also to calculate the imposed voltages on the optical components of the electron gun. Moreover, by applying this code the location and diameter of all the apertures (electrodes) and also the tracing of the electron beams through the electrostatic lenses can be determined. The designed electron gun system accelerates and focuses the electrons leaving a thermionic emitter to an interaction domain (target) in a wide range of variable final energy.

The experimental study of a tapered, multi-gap, multi-aperture pseudospark-sourced electron gun based X-band plasma assisted slow wave oscillator is presented. The designed electron gun is based on the pseudospark discharge concept and has been used to generate a high current density and high energy electron beam simultaneously. The distribution of apertures has been arranged such that the field penetration potency inside the backspace of the hollow-cathode is different while passing through the tapered gap region. This leads to non-concurrent ignition of the discharge through all the channels which is, in general, quite challenging in the case of multi-aperture plasma cathode electron gun geometries. Multiple and successive hollow cathode phases are reported from this electron gun geometry, which have been confirmed using simulations. This geometry also has led to the achievement of ~71% fill factor inside the slow wave oscillator for an electron beam of energy of 20 keV and a beam current density in the range of 115–190 A/cm2 at a working argon gas pressure of 18 Pa. The oscillator has generated broadband microwave output in the frequency range of 10–11.7 GHz with a peak power of ~10kW for ~50 ns. [ABSTRACT FROM AUTHOR]

High-speed video filming is applied to investigate low-pressure (argon 0.053-0.133 Pa) pulsed gas discharge dynamics in a planar magnetron built-in the explosive emission cathode of a high-current electron gun. It has been found that, in the beginning, the discharge starts at the side surface of the cathode and then spreads to its face. The stability of the discharge ignition instant at the cathode face as a function of the working pressure of the gas and the cathode design has been studied. It has been found that the pulsed longitudinal magnetic field results in the discharge switching over in the axial direction onto the electron gun collector. A qualitative explanation of the observed discharge behavior has been given. [ABSTRACT FROM AUTHOR]

This paper presents the electron beam misalignment study with respect to cathode position and cathode magnetic field of 42 GHz, 200 kW gyrotron. The performance of gyrotron is affected with the misalignment of cathode position. The simulation results confirm the tolerance of cathode misalignment with respect to the design parameters such as the transverse-to-axial velocity ratio, the maximum transverse velocity spread, etc. [ABSTRACT FROM AUTHOR]

A practical electron gun including the cathode, the grid, the anode, the insulator, the joint flange, and the gun chamber was developed to build a 90 keV microfocus x-ray source with high performance. Based on the electron emission theory at metal surface, the cathode, the grid, and the anode were optimized to achieve fine crossover, high maximum brightness, and high effective brightness with 1 mA beam current. In order to improve stability of the gun, the grid, the anode, the insulator, the joint flange, and the gun chamber were designed and fabricated to eliminate discharge at the peak and the creepage along insulator. Results show that the effective brightness of this model is 1.05 x 105 A/(cm² sr) with 1 mA beam current, and the microfocus x-ray source has a resolution below 4 µm when the target current is 100 µA. The practical electron gun can improve the beam current quality of the microfocus x-ray source. [ABSTRACT FROM AUTHOR]

Although international thermonuclear experimental reactor project employs the use of beryllium-tungsten system as plasma-facing material in nuclear fusion devices, the scientific fusion community still considers aluminum-tungsten configuration a promising candidate for fusion-related devices, aluminum aiming to be a beryllium replacement. This study provides in-depth x-ray photoelectron spectroscopy results on the interaction of aluminum and tungsten atoms in the surface layers prepared in various gaseous environments, important for the fusion community: vacuum, nitrogen, helium, and oxygen. A surprising outcome of the analysis is the suggested aluminum-tungsten surface alloying even at temperatures below 100 °C as well as the chemical interaction between aluminum and tungsten atoms, with the formation of aluminum tungstate, the two surface processes reinforcing the conclusion of surface mixing metals. Additionally, aluminum has a particular behavior by protecting and maintaining tungsten in an alloyed and unoxidized state for vacuum, nitrogen, and helium plasma environments, while in the presence of oxygen manages to preserve tungsten state of alloying. [ABSTRACT FROM AUTHOR]

We consider a new version of the nonadiabatic system for the formation of a helical electron beam in a gyrotron, in which electrons acquire initial oscillatory velocities when a rectilinear beam is injected at an angle to the magnetic field. In such an electron gun, the influence of thermal electron velocities and roughness of the emitting surface can be decreased, as compared with the conventional electron-optical systems of gyrotrons. This makes it possible to increase significantly the system efficiency. The main factors affecting the quality of the formed beam are considered. [ABSTRACT FROM AUTHOR]

The sensitivity of an electron–ion crossed-beams experiment is mainly determined by the densities of both beams in the interaction region. Aiming at the extension of the available range of accessible electron energies and densities, a new high-power electron gun has been developed and fabricated. It delivers a ribbon-shaped beam with currents of up to 1 A at variable energies reaching 3500 eV at the maximum. The design goals of the gun are being met by using a configuration of electrodes, which allows for a variety of operation modes. Here, we report on the results of the ongoing tests of the new electron gun. In particular, electron-impact ionization cross sections of He + and Xe 5+ ions were measured employing the animated crossed-beams technique. The results are in excellent agreement with literature data. [ABSTRACT FROM AUTHOR]

The linear accelerators (linacs) producing high energy and high power of electron-beam or X-ray beam have been used in medicine, industry, national security, etc. In the linac, the electrons are generated by the electron gun and accelerated in the accelerating column with the high-power RF fields. The high-voltage pulses from the pulse modulator are supplied to the RF power source and the electron gun. The pulse modulator is one of the big and expensive components in the linac. The commercial medical linacs commonly use the pulse modulator based on the thyratron-switched pulse-forming network. In order to improve the power efficiency, achieve the system compactness, and optimize the cost and space, the solid-state pulse modulator based on the Marx generator was proposed. The low-power solid-state pulse modulator was developed for the electron gun operation. The conceptual design and functional results were confirmed. In order to apply it to the RF power source, such as a magnetron or a klystron, the 6-MW pulse modulator with the same Marx scheme is proposed. It consists of 40 storage-switch stages and one high-voltage pulse transformer, producing the pulse of 50 kV and 120 A required by the magnetron in the medical linac. A storage-switch stage was designed for insulated gate bipolar transistors to switch high current of 280 A and 720 V and to use the capacitor of 25~\mu \textF which was chosen for the voltage droop of 10% with the pulsewidth of 5~\mu \texts . The prototype system with eight storage-switch stages was fabricated and tested with a load system. The performance results show that it can be extended to be the 6-MW solid-state pulse modulator. In this paper, we describe the design features, and discuss the results and also the future plan to optimize the solid-state pulse modulator in the medical linac. [ABSTRACT FROM AUTHOR]

We have investigated the dependence of hole mobility on thickness in free-standing films of bisphenol-A-polycarbonate (PC) doped with 30 wt% p -diethylaminobenzaldehyde diphenylhydrazone (DEH). Carrier generation in a time-of-flight (TOF) experiment was achieved through direct ionization of dopant molecules by electron impact using an electron gun supplying pulses of monoenergetic electrons in the range of 2–50 keV. The position of dopant ionization depends upon the electron energy and three TOF variants have been recently developed and used in this study. We have found that the hole mobility generally decreased with increasing film thickness with concomitant acceleration of the post-flight current decay indicating that the transport process approaches the steady-state regime, this process happening slightly faster than our model predicts. Numerical calculations have been compared with experimental data. The results are discussed in detail. The way to reconcile ostensibly contradictory interpretations of our results and those commonly reported in literature relying on photo injection technique has been proposed. [ABSTRACT FROM AUTHOR]

The article presents a crystalline characterization technique that adopts a low-energy electrostatically focused electron gun and a super-aligned carbon nanotube (SACNT) film sample support. Topics discussed include the rapid crystalline characterization of large-area graphene through this technique, the observation of a unique diffraction pattern of adsorbates on the suspended graphene at room temperature and the weak interaction with two-dimensional (2D) materials.

Recent studies of rf breakdown physics in cryogenic copper X-band accelerating structures have shown a dramatic increase in the operating gradient while maintaining low breakdown rates. The TOPGUN project, a collaboration between UCLA, SLAC, and INFN, will use this improvement in gradient to create an ultra-high brightness cryogenic normal conducting photoinjector [16] . The brightness is expected to be higher by a factor of 25 relative to the LCLS photogun [9] . This improvement in the brightness will lead to increased performance of X-Ray free electron lasers (FELs) and ultrafast electron diffraction devices [16] . We present the rf design for this S-band photogun, which will be a drop-in replacement for the current LCLS photogun. [ABSTRACT FROM AUTHOR]

We determine the instrument response of an ultrafast electron microscope equipped with a conventional thermionic electron gun and absent modifications beyond the optical ports. Using flat, graphite-encircled LaB 6 cathodes, we image space-charge effects as a function of photoelectron-packet population and find that an applied Wehnelt bias has a negligible effect on the threshold levels (>10 3 electrons per pulse) but does appear to suppress blurring at the upper limits (∼10 5 electrons). Using plasma lensing, we determine the instrument-response time for 700-fs laser pulses and find that single-electron packets are laser limited (1 ps), while broadening occurs well below the space-charge limit. [ABSTRACT FROM AUTHOR]

Efforts to understand matter at ever-increasing spatial and temporal resolutions have led to the development of instruments such as the ultrafast transmission electron microscope (UEM) that can capture transient processes with combined nanometer and picosecond resolutions. However, analysis by UEM is often associated with extended acquisition times, mainly due to the limitations of the electron gun. Improvements are hampered by tradeoffs in realizing combinations of the conflicting objectives for source size, emittance, and energy and temporal dispersion. Fundamentally, the performance of the gun is a function of the cathode material, the gun and cathode geometry, and the local fields. Especially shank emission from a truncated tip cathode results in severe broadening effects and therefore such electrons must be filtered by applying a Wehnelt bias. Here we study the influence of the cathode geometry and the Wehnelt bias on the performance of a photoelectron gun in a thermionic configuration. We combine experimental analysis with finite element simulations tracing the paths of individual photoelectrons in the relevant 3D geometry. Specifically, we compare the performance of guard ring cathodes with no shank emission to conventional truncated tip geometries. We find that a guard ring cathode allows operation at minimum Wehnelt bias and improve the temporal resolution under realistic operation conditions in an UEM. At low bias, the Wehnelt exhibits stronger focus for guard ring than truncated tip cathodes. The increase in temporal spread with bias is mainly a result from a decrease in the accelerating field near the cathode surface. Furthermore, simulations reveal that the temporal dispersion is also influenced by the intrinsic angular distribution in the photoemission process and the initial energy spread. However, a smaller emission spot on the cathode is not a dominant driver for enhancing time resolution. Space charge induced temporal broadening shows a close to linear relation with the number of electrons up to at least 10 000 electrons per pulse. The Wehnelt bias will affect the energy distribution by changing the Rayleigh length, and thus the interaction time, at the crossover. [ABSTRACT FROM AUTHOR]

A concurrently high beam current and high current density carbon nanotube (CNT) cold cathode electron gun is herein developed. A radial electron source has been realized, formed from CNTs synthesized directly on the side walls of a stainless steel truncated-cone electron gun. Experimental results evidenced a 35 kV/50 mA electron beam can achieve a beam transparency of nearly 100% through the use of double anodes and crossed electric and magnetic fields. A maximum beam current density of 3.5 A/cm 2 was achieved. These results demonstrate the potential impact of coupling novel cold cathode gun architectures and emerging nanomaterials and their collective role in augmenting the performance of incumbent electron gun technologies, alongside allowing for the realization new types of field emission vacuum electron radiation sources. [ABSTRACT FROM AUTHOR]

Angle log-periodic meander line microstrip radial sheet beam traveling-wave tube is one kind of novel minimized vacuum device with low beam voltage. To generate and focus the radial sheet electron beam, a novel radial divergent sheet beam electron optical system, including the tractable radial sheet electron beam gun and miniaturized and feasible radial small tunable periodic cusped magnetic focusing system, is proposed in this paper. The fan-shaped radial sheet beam is emitted from the cylindrical surface cathode, compressed in axial direction, and confined in azimuthal direction by the focusing electrode. Simulation results show that the total emission of the angular radial sheet beam gun is 51.2 mA with the dimensions of 0.26~\text mm \times 8 ° under the voltage of 1.7 kV, and the fan-shaped radial sheet beam can totally pass through the fan-shaped drift tunnel under the magnetic field. The experimental results are good in agreement with the simulation results. The tested angular radial sheet beam transmission efficiency is >90% in an 18.8-mm-length beam tunnel with the fill factor of 50%. [ABSTRACT FROM PUBLISHER]

A project to construct a compact pre-bunched Free Electron Laser by using a normal conducting photocathode electron gun has been undertaken at Inter University Accelerator Centre (IUAC), New Delhi, India. In this facility, the short laser pulses from a high power laser system will be split into many pulses (2–16) commonly known as ‘Comb beam’ and will strike the photocathode material (metal and semiconductor) to produce electron beam bunches. The electrons will be accelerated up to an energy of ∼8 MeV by a copper cavity operated at a frequency of 2860 MHz and the beam will be injected into a compact, planar permanent undulator magnet to produce THz radiation. The radiation frequency designed to be tuned in the range of 0.15–3 THz by varying the magnetic field of the undulator and/or changing the energy of the electron. The separation of the laser micro-pulses will be varied by adjusting the path length difference to alter the separation of the electron micro-bunches and to maximise the radiation intensity. [ABSTRACT FROM AUTHOR]

In this paper we report on simulations and the mechanical design of a high-compression electron gun for an Electron Beam Ion Source (EBIS) dedicated for production of high intensity and high repetition rate pulses of bare carbon ions for injection into linac-based hadron therapy facilities. The gun is presently under construction at CERN to be retrofitted into the TwinEBIS test bench for experimental studies. We describe the design constraints, show results of numeric simulations and report on the mechanical design featuring several novel ideas. The reported design makes use of combined-function units with reduced number of mechanical joints that were carefully controlled and tuned during the manufacturing phase. The simulations addressed a wide range of topics including the influence of thermal effects, focusing optics, symmetry-breaking misalignments and injection into a full 5 T field. [ABSTRACT FROM AUTHOR]

We present the design and fabrication of a micrometer-scale electron gun for the implementation of ultrafast low-energy electron diffraction from surfaces. A multi-step process involving photolithography and focused-ion-beam nanostructuring is used to assemble and electrically contact the photoelectron gun, which consists of a nanotip photocathode in a Schottky geometry and an einzel lens for beam collimation. We characterize the low-energy electron pulses by a transient electric field effect and achieve pulse durations of 1.3 ps at an electron energy of 80 eV. First diffraction images in a backscattering geometry (at 50 eV electron energy) are shown. [ABSTRACT FROM AUTHOR]

Investigations were carried out into the production of combined welded joints in 316L(N) austenitic steel and BrKh1Tsr (CuCrZr) and CuAl10Ni5Fe4 bronzes 30 mm thick by electron beam welding (EBW). The formation of the welded joints in dissimilar materials is investigated and the EBW conditions determined. The microstructure, mechanic properties and chemical composition of the welded joints are also determined. It is shown possible to obtain the mechanical properties of welded joints similar to the properties of the parent bronze by weldbrazing. It is therefore necessary to increase the accuracy and stability of the electron beam parameters as a technological tool. [ABSTRACT FROM AUTHOR]

Four different configurations of plasma cathode electron (PCE) guns have been designed and developed in which pseudospark discharge concept has been used. Experimental studies have been performed to identify the dependence of geometrical design parameters like shape of aperture, distribution of apertures, and the number of gaps between hollow cathode and anode on high-energy and high-current-density electron beam emissions. The beam current density has been increased around five times by changing the shape of aperture from circular to sheet keeping the aperture area and other geometrical parameters identical. The perveance of the electron beam has also been increased by increasing the number of apertures on hollow cathode and anode surface. The beam current density from single aperture to multiple apertures has increased from 225 to 900 A/cm2 with low beam energy for the multiple-aperture case. The multiple gaps between hollow cathode and anode increase the electron beam energy. The maximum beam energy is found to be 16–14.5 keV at an applied gap voltage of 16 kV from the developed multigap PCE gun, which is much higher than that from the single gap configuration. [ABSTRACT FROM PUBLISHER]

The MAX IV facility in Lund, Sweden consists of two storage rings for production of synchrotron radiation. The smaller 1.5 GeV ring is presently under construction, while the larger 3 GeV ring is being commissioned. Both rings will be operating with top-up injections from a full-energy injector. During injection, the electron beam is first delivered to the main injector from a thermionic pre-injector which consists of a thermionic RF gun, a chopper system, and an energy filter. In order to reduce losses of high-energy electrons along the injector and in the rings, the electron beam provided by the thermionic pre-injector should have the correct time structure and energy distribution. In this paper, the design of the MAX IV thermionic pre-injector with all its sub components is presented. The electron beam delivered by the pre-injector and its dependence on parameters such as optics, cathode temperature, and RF power are studied. Measurements are here compared with simulation results obtained by particle tracking and electromagnetic codes. The chopper system is described in detail, and different driving schemes that optimize the injection efficiency for the two storage rings are investigated. During operation, it was discovered that the structure of the beam delivered by the gun is affected by mode beating between the accelerating and a low-order mode. This mode beating is also studied in detail. Finally, initial measurements of the electron beam delivered to the 3 GeV ring during commissioning are presented. [ABSTRACT FROM AUTHOR]

We report on hot test measurements of a wide-bandwidth, 220-GHz sheet beam traveling wave tube amplifier developed under the Defense advanced research projects agency (DARPA) HiFIVE program. Nano-computer numerical control (CNC) milling techniques were employed for the precision fabrication of double vane, half-period staggered interaction structures achieving submicrometer tolerances and nanoscale surface roughness. A multilayer diffusion bonding technique was implemented to complete the structure demonstrating wide bandwidth (>50 GHz) with an insertion loss of about −5 dB achieved during transmission measurements of the circuit. The sheet beam electron gun utilized nanocomposite scandate tungsten cathodes that provided over 438-A/cm2 current density in the 12.5:1 ratio sheet beam. An InP HBT-based monolithic microwave integrated circuit preamplifier was employed for TWT gain measurements in the stable amplifier operation region. In the wide-bandwidth operation mode (for gun voltage of 20.9 kV), a gain of over 24 dB was measured over the frequency range of 207–221 GHz. In the high-gain operation mode (for gun voltage of 21.8 kV), over 30 dB of gain was measured over the frequency range of 197–202 GHz. High-power tests were conducted employing an extended interaction klystron. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

Typical use of colloidal quantum dots (QDs) as bright, tunable phosphors in real applications relies on engineering of their surfaces to suppress the loss of excited carriers to surface trap states or to the surrounding medium. Here, we explore the utility of QDs in an application that actually exploits their propensity toward photoionization, namely within efficient and robust photocathodes for use in next-generation electron guns. In order to establish the relevance of QD films as photocathodes, we evaluate the efficiency of electron photoemission of films of a variety of compositions in a typical electron gun configuration. By quantifying photocurrent as a function of excitation photon energy, excitation intensity and pulse duration, we establish the role of hot electrons in photoemission within the multiphoton excitation regime. We also demonstrate the effect of QD structure and film deposition methods on efficiency, which suggests numerous pathways for further enhancements. Finally, we show that QD photocathodes offer superior efficiencies relative to standard copper cathodes and are robust against degradation under ambient conditions. [ABSTRACT FROM AUTHOR]

Equipping the adjustable horizontal focusing electrodes (FEs), a dual mode electron gun providing different current beams, has been proposed and evaluated. Employing this tunable FE electron gun, a continuous wave (CW)/pulsed dual mode, 0.2-THz sheet beam traveling wave tube (SB-TWT) has been designed. The tube employs a high density and high current sheet beam for pulsed mode operation, and a reduced size and lower current sheet beam for the CW mode. This scheme provides CW mode increased efficiency and higher beam transmission factor than other, more conventional, dualmode techniques such as by changing the RF drive power. Using a 1.2-T uniform focusing magnetic field, both beams are predicted to have excellent transmission factor (more than 99%) to the collector through the 65-mm beam tunnel. Driven by the pulsed, high current electron beam, the 0.2-THz SB-TWT exhibits more than 100-W power over a 20-GHz bandwidth. Driven by the low current electron beam, the tube provides 20-dB gain and 10-W CW output power over the required bandwidth of 0.19 THz–0.21 THz. [ABSTRACT FROM PUBLISHER]

An apparatus for electron-beam transportation to air has been developed on the basis of an electron gun with a plasma emitter. A pressure drop from values of (1-3) × 10 Torr in an accelerating gap to an air pressure of 760 Torr is produced by the differential pumping system. Usually, no less than three pumping stages are used in apparatuses based on hot-cathode guns for electron-beam transportation to air because of the need to maintain the pressure in the hot-cathode area at a level of 10 Torr. It is possible to simplify the differential pumping system by reducing the number of stages to two via to the use of a gun with a plasma emitter. The construction of an apparatus for electron-beam transportation to air is described and its key characteristics are presented. [ABSTRACT FROM AUTHOR]

The optimization of welds obtained by electron beam welding is a multi-criterial task, involving the requirements for the geometrical characteristics of the welds, together with the fulfilment of the requirements for lack of defects. This complex task can be solved through estimation of adequate models for the dependencies of the quality characteristics on the process parameters and finding optimal solutions that fulfil simultaneously all criteria. In this paper, only the appearance of critical defects at certain regime conditions is considered, without taking into account of the type or the number of the defects. The modelling is done by implementation of two approaches - statistical approach based on regression analysis and discriminant analysis for defining the areas of the process parameters, where the appearance of defects is or is not expected. Different modelling approaches are compared and their applicability is discussed. Experimental data are used for the investigation of the influence of the variation of different electron beam welding regime conditions - electron beam power, welding velocity, the distances from the main surface of the magnetic lens of the electron gun to the beam focusing plane and to the sample surface on the considered performance characteristics. [ABSTRACT FROM AUTHOR]

With the aim to create a simpler structure and reduce the production cost of an existing Schottky emitter-scanning electron microscope (SE-SEM), the authors have built and tested a double-O-ring electron gun which is also compatible with ultrahigh vacuum (UHV). Specifically, the gun and column of the SEM consist of low-carbon steel, of which the magnetic shielding effect is greater than that of stainless steel, allowing magnification of ×200000 in the adapted SEM base without additional magnetic shielding material, such as permalloy or mu-metal. The position of the electron gun can be adjusted along the horizontal axis while maintaining the UHV condition. Excellent beam current stability with less than 1% variation for more than 1 h was noted. Therefore, the authors anticipate that the double-O-ring electron gun and column of low-carbon steel together represent an inexpensive and uncomplicated SE-SEM compared to existing types. [ABSTRACT FROM AUTHOR]

Beam deflection induced by E×B near a linear filament cathode in a two grid electron gun is presented theoretically and experimentally. The experimental results are consistent with the calculation based on the theoretical equations. The influences upon performance and design of electron gun with linear filament cathode, which is used broadly in electrocurtain accelerators, are discussed in detail. [ABSTRACT FROM AUTHOR]

Here, we investigate, through parametrically optimized macroscale simulations, the field electron emission from arrays of carbon nanotube (CNT)-coated Spindts towards the development of an emerging class of novel vacuum electron devices. The present study builds on empirical data gleaned from our recent experimental findings on the room temperature electron emission from large area CNT electron sources. We determine the field emission current of the present microstructures directly using particle in cell (PIC) software and present a new CNT cold cathode array variant which has been geometrically optimized to provide maximal emission current density, with current densities of up to 11.5 A/cm2 at low operational electric fields of 5.0 V/μm. [ABSTRACT FROM AUTHOR]