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We consider an example of implementation of a multi-barrel gyrotron. The simplest scheme of the multi-barrel gyrotron combines the advantages of both the canonical gyrotron and the gyrotron with the near-axis beam as the system of formation of helical electron beams and efficient selection of modes synchronous with high gyrofrequency harmonics, respectively, and is attractive from the viewpoint of applications that require moderate power levels. The design of a multi-barrel gyrotron with the possibility of simultaneous generation at frequencies of 263, 395, and 526 GHz is presented. Additionally, the possibility of generating the radiation at a frequency of 594 GHz is considered. Such frequencies are required for DNP/NMR facilities with proton Larmor frequencies of 400, 600, 800, and 900 MHz, respectively. Along with the conventional scheme of radiation output towards the collector, the features of the scheme with the radiation output toward the electron gun are considered. [ABSTRACT FROM AUTHOR]

Summary: We report on our progress to develop and optimize electron sources for practical applications. A simple fabrication process is introduced based on a wafer dicing saw and a wet chemical etch step without the need for a clean room. Due to the formation of crystal facets the samples show a homogeneous geometry throughout the array. Characterization techniques are developed to systematically compare various arrays. A very defined measurement procedure based on current controlled IV‐sweeps as well as lifetime measurements at various currents is proposed. To investigate the current distribution in the array a commercial CMOS detector is used and shows the potential for in depth analysis of the arrays. Finally, a compact hermetically sealed housing is presented enabling electron generation in atmospheric pressure environments. [ABSTRACT FROM AUTHOR]

We present the design and performance of a compact ultrafast electron diffraction instrument. The diffractometer provides a means of examining time-resolved ultrafast dynamical properties of solids. The system's utilization is discussed in terms of instrument parameters and diffraction data from selected condensed matter samples. The difractometer's performance is highlighted in terms of detection sensitivity, instrumental temporal resolution, and the electron beam transverse coherence length. Following specific details of the construction, we present a practical discussion of parameters such as repetition rate and provide advice on general construction approaches for laboratory-based, keV ultrafast electron diffractometers. In addition, design guidance for constructing a compact electron gun source that is well-suited for studying diffraction from hard condensed matter is given. A unique data acquisition scheme, utilizing high laser repetition rates, is presented. [ABSTRACT FROM AUTHOR]

In this work, we present observations about the transport of 15.2 keV electrons with a beam current of 21 μA through macroscopic dielectric capillaries. These capillaries are made of borosilicate glass with an inner diameter of about 6 mm, and samples with a bending angle of 90° and 360° were investigated. The electron gun was adjusted, and the beam injected into the capillary had a current of 21 μA and a divergence half angle of about 0.75°. A retarding field analyzer (RFA) was installed at the outlet of the capillary to collect the transported current and to investigate the particle energy of exiting electrons (Fig. 1). The transport of electrons to the outlet occurred nearly instantaneous in both capillaries, and the RFA at the outlet detected a current of around 20 μA for both capillary samples resulting in a transmission coefficient of over 95%. Energy measurements showed that the particle energy at the outlet is only at several electron volts, which reveals that electrons lost almost all of their incident energy while traveling through the capillary. A large amount of exiting particles are most likely secondary electrons emitted from the capillary sample. The fact that transmission coefficients for both samples are similarly high, and that the particles can still be transported through the 360° capillary although most of their energy is already lost at 90°, results in many questions that shall be investigated in further studies. The capillaries showed a blueish glow during electron transmission due to cathodoluminescence effects. [ABSTRACT FROM AUTHOR]

This paper presents the design, prototype engineering, and initial testing of a relatively low-voltage, high aspect ratio electron gun for versatile pulsed power applications. The sheet beam, diode electron gun is designed for (23–25) kV voltage and 6 µA/V1.5, as is required for x-band klystron, as a part of a compact Klylac delivering electron beam energy in the MeV range. The gun prototype was engineered, built, and tested using a Scandinova M1-0.5 modulator. Beam loss on the anode aperture is evaluated from transient waveforms and equivalent circuit modeling. [ABSTRACT FROM AUTHOR]

In this paper, an angular radial extended interaction amplifier (AREIA) that consists of a pair of angular extended interaction cavities is proposed. Both the convergence angle cavity and the divergence angle cavity, which are designed for the converging beam and diverging beam, respectively, are investigated to present the potential of the proposed AREIA. They are proposed and explored to improve the beam–wave interaction capability of W-band extended interaction klystrons (EIKs). Compared to conventional radial cavities, the angular cavities have greatly decreased the ohmic loss area and increased the characteristic impedance. Compared to the sheet beam (0°) cavity, it has been found that the convergence angle cavity has a higher effective impedance and the diverging beam has a weaker space-charge effect under the same ideal electron beam area; the advantages become more obvious as the propagation distance increases. Particle-in-cell (PIC) results have shown that the diverging beam (8°) EIA performs better at an output power of 94 GHz under the condition of lossless, while the converging beam (−2°) EIA has a higher output power of 6.24 kW under the conditions of ohmic loss, an input power of 0.5 W, and an ideal electron beam of 20.5 kV and 1.5 A. When the loss increases and the beam current decreases, the output power of the −2° EIA can be improved by nearly 30% compared to the 0° EIA, and the −2° EIA has a greatly improved beam–wave interaction capacity than conventional EIAs under those conditions. In addition, an angular radial electron gun is designed. [ABSTRACT FROM AUTHOR]

Nitrogen ions were implanted at different energies of 15, 30, 45 and 60 keV and with the flux of 1017 N+cm−2 inside the nickel layers that have been deposited on the 304 stainless steel using the electron gun method at room temperature. XRD patterns showed different crystalline phases of nickel nitride for the implanted samples. The surface morphology was extracted by MountainsMap software's using statistical data from AFM analysis. In addition, a potentiodynamic polarisation test was performed in a 3.5% NaCl solution to study the corrosion behaviour. These studies revealed that corrosion was directly related to the deposition parameters, mainly the implantation energy, modifying the surface so that the highest corrosion resistance was obtained for the sample implanted with 60 keV. [ABSTRACT FROM AUTHOR]

An algorithm is presented that extends the application of ray optics to charged particle guns, where particles are emitted with a wide range of angles and relative energies. The extension is made possible by replacing the ray tangent as a coordinate with the directional sine, which remains finite for all take-off angles, and if necessary, by simulating the ray optics for multiple segments of the energy distribution. Consequently, an electron gun comprising a cathode, an extractor, and an anode, for example, may be characterized by its focal length, the location of its image plane, the magnification of the emission spot at this plane, and the primary and higher-order aberrations of the module, which reshape this spot. This description is realized by modeling the particle trajectories as a power series in their initial conditions and by using standard algebraic techniques, namely, the binomial and Taylor expansions, to transform the relativistic Newton's equation, which describes the evolution of the trajectories in the electromagnetic fields of the gun, into a differential equation for the evolution of the series coefficients. In addition to providing the optical parameters, the series coefficients produce an algebraic map between the particle coordinates along the gun axis and their initial values at the plane of emission, thereby circumventing the need to launch a multitude of trajectories in a particle simulator to model the source that the gun presents to the optical elements downstream. The algorithm may be enhanced in the future by incorporating some effects of space charge from the emission current. [ABSTRACT FROM AUTHOR]

In the past decade, the fourth-generation light source based on the combination of Energy Recovery Linac (ERL) and Free-Electron Laser (FEL) using superconducting linear accelerators has garnered significant attention. It holds immense potential, particularly in generating high-power Extreme Ultraviolet (EUV) light sources. This article primarily focuses on the physical design of an injector for ERL-FEL, based on a Very High Frequency (VHF) electron gun with a charge of 100 pC. The beam energy is accelerated to 10 MeV using 3-cell superconducting cryomodule. The optimization of beam parameters is conducted through employment of BMad and ASTRA simulations, incorporating the concept of Merger optimization. The beam emittance is less than 0.6 mm mrad, and the peak current at the injector exit exceeds 18 A. We present a new method to evaluate the Longitudinal Space Charge (LSC) effects in merger sections, which can be readily applied in design work. Furthermore, we introduce a novel type of merger. The performance of this new merger is comparable to the previously known optimum, the zigzag merger, offering a potential alternative solution for injectors in ERLs. [ABSTRACT FROM AUTHOR]

The High Brilliance Neutron Source (HBS) is a High-Current Accelerator-driven Neutron Source (HiCANS) under development at Jülich Centre for Neutron Science - Forschungszentrum Jülich. The unique specifications of the HBS require a neutron target with a high neutron emission able to operate in vacuum with a 70 MeV proton beam with 90 mA peak current and 1.6% duty cycle leading to an average thermal load of 100 kW. A tantalum target of 100 cm2 irradiated area with an internal cooling structure which removes the heat quite homogeneously, provides a good compromise between low pressure and high heat transfer and ensures an homogeneous protons energy loss was designed and optimized by means of MCNP, CFD and FEM simulations. Such a target was successfully manufactured and its operational capability was demonstrated by operating it under a heat load of 1 kW cm−2 from an electron gun. • High power neutron target for high current accelerator-driven neutron source (HiCANS). • Tantal target for neutron generation at 70 MeV proton beam. • up to 1 kW cm−2 thermal heat dissipation from a stationary solid target via micro channel water cooling. [ABSTRACT FROM AUTHOR]

A large research effort is currently ongoing within the framework of the EUROfusion consortium for the study and design of a water-cooled lithium–lead (WCLL) breeding blanket (BB). This concept will be tested in ITER through the installation of a test blanket module (TBM) and it is one of the two candidates adopted as driver BBs in DEMO. In this framework, at the ENEA research centre of Brasimone, the realization of the experimental platform, W-HYDRA, is envisaged. The platform is dedicated to the support of the development of WCLL BB and ITER TBM and the investigation of the DEMO balance of plants. One of the most important experimental infrastructures is the water-loop facility, the aim of which is to provide water at a high pressure and temperature (PWR conditions), with a sufficient mass-flow rate and power for the experimental testing of BB and TBM components. The facility will be equipped with a vacuum chamber and an electron beam gun for the reproduction of high surface heat flux on plasma-facing components. In the present work, the design of a prototypical mock-up (MU) of the WCLL BB first wall is described. The MU is used to investigate the thermal, hydraulic and structural behavior of the current first-wall design under relevant heat loads at the expected operational conditions. The delineation of the main experimental test's features and the instrumentation needed is assessed in the paper. A preliminary CFD calculation on the prototypical MU and the computational results are also presented. [ABSTRACT FROM AUTHOR]

The elements of repair technology of electron beam welding in the manufacture of a metal-ceramic cathode unit of a powerful welding electron beam gun are considered. A low degree of heat generation at the place of weld overlapping inherent in electron beam welding reduces the risk of buckling parts being joined and provides the maximum compliance with the required sizes of the unit. The need in repair of the cathode unit was determined by the cases of supplying imported insulators with defects in the form of deviations of a thickness from 0.5 to 1.0 mm in the wall of the metal flange («collar») in the brazed joint with the insulator. It was necessary to eliminate the consequences of a violation of the mechanical treatment of the insulator collar after brazing. The possible ways and schemes of repair technologies of such units are shown that allow avoiding the rejection of valuable parts and transferring them to the category of those subjected to restoration. The presented repair technologies involve the use of circumferential insertsbandages of different configuration for two variants to eliminate welding defects associated both with local repair of the edge as well as with repair of its quite elongated areas. Due to a correct choice of the shape of repair inserts, the use of some technological methods and observance of the accuracy of assembly and the sequence of repair welding, it became possible to preserve geometric dimensions and to ensure the functionality of the welded assembly as a whole. 6 Ref., 6 Tabl., 6 Fig. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) show significant advantages in the development of cold cathode X-ray tubes due to their excellent field emission performance; however, there are still some problems, such as short lifetime and the low emission current of large-area CNTs. In this paper, a front-grid carbon nanotube array model was established, and the electric field intensity near the tip of the CNTs' electric field enhancement factor was analytically calculated. A simulation model of a CNT three-dimensional field emission electron gun was established by using computer simulation technology (CST). The effects of grid wire diameter, grid aperture shape, and the distribution of grid projection on the cathode surface on the cathode current, anode current, and electron transmission efficiency were analyzed. The aperture ratio was used to evaluate the grid performance, and the simulation results show that the ideal aperture ratio should be between 65 % and 85 % . A grid structure combining a coarse grid and a fine grid was designed, which can make the electric field intensity around the grid evenly distributed, and effectively increased the cathode emission current by 24.2 % compared with the structure without the fine grid. The effect of grid aperture ratio on the electron transmission efficiency was tested. The simulation results and optimized structure can provide a reference for the grid design of cold cathode emission X-ray tubes. [ABSTRACT FROM AUTHOR]

The influence of the thermal state of process-gun elements and their relative arrangement on electron-optical system operation and the beam parameters is studied that are generated. A thermal-heating model of the cathode assembly of the ELA-60B electron gun is developed. To check the model, an experimental bench is developed on the basis of the ELA-15I electron-beam unit, which allows recording the cathode and gun-body temperature, as well as the cathode heating power. The temperature of the cathode and the gun body in the stationary section are used as verification parameters, as well as the temperature dependences in the area of natural cathode cooling and heating of the gun body. Thermal contacts between the contacting surfaces of the cathode assembly are used as debugging model nodes. Cathode assembly deformations are calculated on the basis of temperature fields. To assess the influence of the deformations, a trajectory analysis is carried out, followed by the construction of a current–voltage characteristic. The real current–voltage characteristic of the ELA-60B electron gun is obtained. As a result of strain analysis, it is found that, when heated, the cathode moves forward relative to the control electrode, moving closer to the anode. The control electrode also lengthens and approaches the anode. The trajectory calculation shows that thermal deformations lead to a change in the operating conditions of an electron-optical lens. The current–voltage characteristic shifts to the right, thereby shifting the gun opening boundary, and the beam crossover drops lower towards the anode, which, in turn, leads to a change in the position of the beam focal plane. [ABSTRACT FROM AUTHOR]

The elements of repair technology of electron beam welding in the manufacture of a metal-ceramic cathode unit of a powerful welding electron beam gun are considered. A low degree of heat generation at the place of weld overlapping inherent in electron beam welding reduces the risk of buckling parts being joined and provides the maximum compliance with the required sizes of the unit. The need in repair of the cathode unit was determined by the cases of supplying imported insulators with defects in the form of deviations of a thickness from 0.5 to 1.0 mm in the wall of the metal flange ("collar") in the brazed joint with the insulator. It was necessary to eliminate the consequences of a violation of the mechanical treatment of the insulator collar after brazing. The possible ways and schemes of repair technologies of such units are shown that allow avoiding the rejection of valuable parts and transferring them to the category of those subjected to restoration. The presented repair technologies involve the use of circumferential inserts-bandages of different configuration for two variants to eliminate welding defects associated both with local repair of the edge as well as with repair of its quite elongated areas. Due to a correct choice of the shape of repair inserts, the use of some technological methods and observance of the accuracy of assembly and the sequence of repair welding, it became possible to preserve geometric dimensions and to ensure the functionality of the welded assembly as a whole. [ABSTRACT FROM AUTHOR]

The design and some characteristics of a source of radially converging low-energy (5–25 keV) high-current electron beams of microsecond pulse duration, which is aimed at surface modification of cylindrical parts and samples, are presented. The cathode unit of the source is a duralumin ring with an 8-cm inner diameter in which which 18 resistively decoupled arc plasma sources are built-in. The operability of the source electron gun in the vacuum-diode (with a residual-gas pressure of ~0.013 Pa) and gas-filled-diode modes at pressures of 0.05–0.09 Pa has been demonstrated. The beam energy density on the 1-cm-diameter anode is sufficient for surface melting of copper (the threshold of pulsed copper melting is 5–5.5 J/cm2 at a pulse duration of 2–3 µs) at a 17-kV charging voltage of the high-voltage pulse generator that powers the electron gun. [ABSTRACT FROM AUTHOR]

In this paper, the design and construction process of a traveling wave electron linear accelerator is presented briefly. The machine consists of an electron gun followed by a prebuncher, a traveling wave buncher, an accelerating tube and the diagnostics instruments. Solenoid magnets provide the beam focusing. A klystron has been used as the RF power source. The linac components are controlled and monitored by a comprehensive control system. All the sub systems of this accelerator are designed and developed based on the domestic technology. The output beam has a maximum energy of 4.5 MeV. The beam parameters like energy, intensity, transverse size and emittance are measurable and tunable. The IPM Linac is a unique tool for experimental R&D in accelerator and beam physics in Iran.

Electron-optic systems (EOSs) with high compression are required for THz-band vacuum-tube electron devices to reduce the cathode load, which is necessary to increase lifetime and enable operation in a continuous-wave (CW) mode. However, it is difficult to achieve high compression of multiple electron beams. In this article, we present the design and simulation of EOS with triple elliptic electron beam for a 0.2-THz traveling-wave tube. The triode electron gun with planar electrodes provides $3\times 0.06$ -A electron beam with compression factor of 16. At the cathode, the current density is 26.31 A/cm2 while in the beam tunnel it is higher than 400 A/cm2. The magnetic focusing system with 1.34-T axial magnetic field consisting of Nd–Fe–B permanent magnets and pole pieces is also designed. The numerical simulation predicts stable beam transmission at 25-mm distance.

This article establishes a very important part of the transmission line (TL) design of the novel 6 MeV compact particle accelerator. Practically, the entire new array of particle accelerators has been designed and is in the final stages of construction at the Ariel University. Except for a novel hybrid photo-cathode electron gun, which has been developed and built in University of California, Los Angeles's Laboratory, it was commissioned at The Schlesinger Family Center for Compact Accelerators, Radiation Sources and Applications (free electron laser) as a part of an ongoing collaboration between the two universities. In this work, we have built a complete simulator for the analysis and propagation of terahertz pulses through the TL, which meets our specific requirements with a high level of flexibility. To simulate the propagation of an output wave packet of the source through the TL quasi-optical system, the original wave packet is decomposed in terms of free-space Hermite–Gaussian basis while the following transformations of the wave packet is described by the transfer matrices technique. Total radiation losses and spectral properties of the TL transfer are analyzed. [ABSTRACT FROM AUTHOR]

Improving the thruster efficiency is a crucial challenge for the development of space electric propulsion systems, especially advanced air-breathing thrusters utilizing the surrounding rarefied atmosphere as fuel. A significant reduction in thruster power consumption can be achieved by using field emission (FE) cathodes that do not require heating and have the highest energy efficiency. In this work, we study FE from nano-graphite thin films, consisting of carbon nanostructures with a high aspect ratio, and demonstrate their suitability for use in the space electric propulsion systems. The films shown appropriate FE characteristics in a wide range of gas pressures at high current loads in constant and pulsed operation modes. Based on the obtained experimental results, nano-graphite cathodes were employed for the design of an electron gun with increased reliability and minimized energy losses associated with electron extraction. The possibility of using such a gun in a specific air-breathing satellite operating in low Earth orbits is demonstrated. [ABSTRACT FROM AUTHOR]

Industrial Electron Linacs have become popular tools for a multitude of radiation technology applications in the fields of material modification, pollution control as well as national security. Although thousands of accelerators are being regularly used, failure analysis of Industrial Electron Accelerators remains a sparsely researched topic and not much information is available in public. Being an economically viable option, industrial electron accelerators need to have a 24 × 7 reliable operation. Hence, it is necessary to understand the failure modes and their mitigation techniques, so that the operation of the accelerators is stable, consistent and safe. In this study, failure mode analysis and identification of degradation mechanisms in an industrial 10 MeV RF electron linac have been studied, with emphasis on the electron gun. Failure modes of the linac and its sub-systems have been investigated. Failure Mode and Effects Analysis and Fault Tree Analysis techniques have been examined for the electron gun. Bayesian Networks are used for modelling the performance of electron gun sub system, utilising the operational data of the RF linac. This approach has facilitated the evidential reasoning process to investigate most probable mode of failure and preventive measures have been recommended for mitigation of failure. [ABSTRACT FROM AUTHOR]

Negative Electron Affinity (NEA) activated GaAs photocathodes are the most popular option for generating a high current (> 1 mA) spin-polarized electron beam. Despite its popularity, a short operational lifetime is the main drawback of this material. Recent works have shown that the lifetime can be improved by using a robust Cs–Sb–O NEA layer with minimal adverse effects. In this work, we operate GaAs photocathodes with this new activation method in a high voltage environment to extract a high current. We demonstrate that improved chemical resistance of Cs–Sb–O activated GaAs photocathodes allowed them to survive a day-long transport process from a separate vacuum system using a vacuum suitcase. During beam running, we observed spectral dependence on lifetime improvement. In particular, we saw a 45% increase in the lifetime at 780 nm on average for Cs–Sb–O activated GaAs compared to Cs–O activated GaAs. [ABSTRACT FROM AUTHOR]

Intense charged particle beams will generally be formed with an initial correlation between their longitudinal properties, including longitudinal variations in current, and their transverse properties, including their radius and divergence. This is due to the competition between the transverse focusing fields in the beam source and the time-varying space charge forces in the beam. In DC electron guns where the current modulation is slow compared to the electron transit time, the nature of these correlations was previously shown to depend on the gun geometry, exhibiting a linear dependence of the beam radius and divergence on the beam current at the gun exit. Here, we extend the previous work to study the transport of beams with such correlation in uniform and periodic solenoid channels. For each transport channel configuration studied, the transverse envelope equation is used to calculate the envelope of 101 beam slices differing in their slice currents, as well as initial radius and divergence (due to their dependence on slice current). For each channel configuration, these calculations are performed 546 times, with each of these iterations considering a different degree of correlation between the radius and divergence, and the slice current. It is found that some degree of correlation between the initial radius and slice current actually aids in beam transport, and the required strength of correlation can be estimated with simple models. Increasing the degree of correlation between the initial divergence and slice current is generally counterproductive, and the degree of sensitivity to such correlations depends on the design of the transport channel. [ABSTRACT FROM AUTHOR]

• Ultrasonic microfluidics under continuous cooling crystallization was introduced as a process intensification approach. • The process was intensified by precipitating an average ezetimibe 101 ± 1.1 nm nano-drugs under best parametric condition. • Ultrasonic frequency, flow rate ratio, and bath temperature were the significant factors for the response EZB PS using PBD. The current research focuses on the antisolvent precipitation of Ezetimibe (EZB) via microfluidics under continuous ultrasonic cooling crystallization. One factor at a time was applied to study the effect of parameters: organic-aqueous flow rate ratio (1:2–1:5), EZB concentration (2.5–12.5, mg/mL), polymer concentration (0.025–0.3, % w/v), ultrasonic frequency (22–42, kHz), ultrasonic bath temperature (10–25, °C), ultrasonic amplitude (20–100, %), confluence angle of micromixer inlet (90°–180°) on the particle size (PS, nm), % yield, % encapsulation efficiency (% EE), and % dissolution rate (% DR). A PBD (Plackett–Burman design) was also employed for the screening studies of influencing factors for aforementioned responses. PS, Zeta potential (ZP, mv), Field Emission Gun Transmission Electron microscope (FEG-TEM), and X-ray diffraction (XRD) were analyzed for raw EZB and nano-precipitated EZB. An average EZB PS of 101 ± 1.1 nm, PDI of 0.027 ± 0.01, 80 ± 1.7 % yield, 78.83 ± 0.5 % DR, 90.67 ± 0.1 % EE, and −20 mV ZP were obtained under best parametric condition. FEG-TEM revealed the final nano EZB morphology was likely to be elongated cuboidal or rod-shaped. An approximately 5-fold increase in %DR was observed for the confluence angle of 90° (├ shaped) micromixer as compared to raw EZB. However, 94.14 % decreament in avg EZB PS was achieved for the confluence angle of 90° (├ shaped) micromixer and utilizing ultrasonic microfluidic system (USMS) under cooling crystallization as a process intesification approach. [Display omitted] [ABSTRACT FROM AUTHOR]

The incident beam quality at the target determines the resolution and intensity of micro-focus X-ray sources, which depends greatly on the focusing system and the target. To meet different spatial layouts of the focusing system with transmission and reflection targets, three-dimension (3-D) modelling of the focusing system was built with Monte Carlo simulation and coordinate transforming method in this paper. In the proposed approach, the focusing system was first optimized by a 2-D model to achieve a fine beam spot with high effective current at the optimum working distance for the transmission and reflection targets. Then, 3-D practical model of the focusing system was achieved by tracing N electrons from the electron gun in three directions using the 5-order Runge-Kutta method. Finally, examples of the focusing system for 90 keV and 30 keV X-ray sources were given to get the energy distributions at transmission and reflection targets. Results show that resolutions of 4 μm and 500 nm have been achieved for 90 keV X-ray source with the transmission target and 30 keV X-ray source with the reflection target respectively. Compared with the experimental results, 2-D modelling of the focusing system is also applicable for X-ray source with the transmission target while 3-D modelling of the focusing system is essential for X-ray source with the reflection target. In addition, the 3-D electron beam model will simplify the design of the real apertures, liner tubes, beam blankers etc. [ABSTRACT FROM AUTHOR]

An Electron Beam Probe (EBP) is preferable to provide a non-interceptive measurement of the transverse distribution of a dense bunched ion beam. During EBP operation, it was observed that the electron beam spot subjects to expansion when scanned across the ion beam due to the strong space charge field of the ion bunch, leading to significant degradation of spatial resolution. To mitigate this effect, a small electron beam spot is beneficial as demonstrated in previous research. This paper presents design details of a low-emittance, small-spot, and long-work-distance electron gun. Geometry optimization of the gun and focus lens is conducted using a multiobjective genetic algorithm (MOGA) interfaced with space charge simulation codes to maintain normalized thermal emittance within an acceptable increase and achieve a small spot at a long work distance. The emittance is measured using a slit-screen technique, resulting in a norm. rms emittance of 0.046(+-0.005) um*rad under low beam current conditions (50 nA). In high-resolution mode, a beam spot size of 0.6 mm (rms) is achieved at a work distance of 1.2 m with the combination of Einzel lens and solenoid. The gun has been successfully operated as part of EBP experiments for accurate and high-resolution measurement of ion beam width, demonstrating excellent agreement with wire scanner measurements with relative deviation not exceeding 1%. [ABSTRACT FROM AUTHOR]

Ultrafast electron diffraction techniques that employ relativistic electrons as a probe have been in the spotlight as a key technology for visualizing structural dynamics which take place on a time scale of a few femtoseconds to hundreds femtoseconds. These applications highly demand not only extreme beam quality in 6-D phase space such as a few nanometer transverse emittances and femtosecond duration but also equivalent beam stability. Although these utmost requirements have been demonstrated by a compact setup with a high-gradient electron gun with state-of-the-art laser technologies, this approach is fundamentally restricted by its nature for compressing the electrons in a short distance by a ballistic bunching method. Here, we propose a new methodology that pushes the limit of timing jitter beyond the state-of-the-art by utilizing consecutive RF cavities. This layout already exists in reality for energy recovery linear accelerator demonstrators. Furthermore, the demonstrators are able to provide MHz repetition rates, which are out of reach for most conventional high-gradient electron guns. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]

This paper introduces the detailed design scheme of a multi-beam electron gun applied to an S-band high power multi-beam klystron. The multi-beam gun adopts a coaxial cavity arrangement, and the total number of electron beams are 40 (19 in the inner layer and 21 in the outer layer). The working voltage of the electron gun is 60 kV, the total current is 300 A (evenly distributed on 40 electron beams), and the single beam perveance is 0.51 μP. The total perveance is 20.4 μP. The cathode loading of the gun is 12 A/cm2, which can meet the requirements of cathode operational lifetime. The beam focusing system uses a periodic reversal permanent magnet to realize miniaturization of the klystron. [ABSTRACT FROM AUTHOR]

The electron optical systems (EOS) play a vital role in vacuum electron devices (VED). This letter reported the design and experiments of the sheet EOS for the 1.03 THz traveling wave tube (TWT). A high-current-density sheet electron beam (SEB) electron gun generating up to 20.3-mA at 22.4-kV is designed, based on the requirements of this TWT. Due to the very high operating frequency, more than 1 THz, the miniature tunnel and beam waist with a dimension of 0.05 mm * 0.148 mm and 0.025 mm * 0.114 mm, respectively, will lead to a very high beam current density (906.9 A/cm2). Therefore, a 1-Telsa uniform magnetic system is designed, to ensure such a high-current-density SEB passes through the 27-mm tunnel. Finally, the primary experiments indicate that 7.56-mA current reaches the collector. [ABSTRACT FROM AUTHOR]

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In this article, the design of a fourth-harmonic gyrotron with 1-kW-level output power at 1 terahertz (THz) is presented. A unique advantage of this design is that, with a well-optimized magnetic-cusp large-orbit electron gun, the designed gyrotron can operate from first-harmonic to fourth-harmonic in multiple discrete bands by varying the confining magnetic field strength. By carefully balancing the competing modes, the gyrotron can be tuned to operate at six candidate modes, including TE1,2 for fundamental harmonic, TE2,3 and TE2,4 for second-harmonic, TE3,5 and TE3,6 for third-harmonic, and TE4,8 for fourth-harmonic interactions. As the main operating mode, the TE4,8 can generate a peak output power of 1.68 kW, with an output efficiency of about 2.1%, and a magnetically controlled frequency tuning range of about 1.5 GHz around 1 THz. The impact of the longitudinal nonuniformity of the cavity at high-harmonic interaction was also studied. It shows that a radial tolerance of several micrometers will significantly elevate the start-oscillation current and deteriorate output performance. This design is to produce a THz source with ultra-wideband tuning capability ranging from the submillimeter-wave to 1-THz bands. [ABSTRACT FROM AUTHOR]

For insulators, the accumulated charge on the surface after electron bombardment will interfere with the total electron emission yield (TEEY) measurement. This work develops a novel method to automatically measure the TEEY of insulators based on self-terminating charge neutralization using two neutralization electron guns. We perform theoretical analysis and experimental design for the neutralization of positive and negative charges. Positive charges are neutralized by an electron gun whose cathode is equipotential to the sample. Negative charges are neutralized by another electron gun whose cathode is adjusted to a negative potential with respect to the grounded sample, which is set between EP1/e and EP2/e. We test the control and stability performance of the TEEY measurement system based on the timing design of the electron gun switching and believe that it meets the TEEY measurement requirements. The TEEY measurements of glass, Si, and SiO2 are in good agreement with the data reported in the references, which validates the accuracy of our method in this work. We anticipate that our method provides an essential reference for the rapid TEEY measurements of insulators. [ABSTRACT FROM AUTHOR]

The Electrostatic Charging Laboratory for Interactions between Plasma and Spacecraft (ECLIPS) research vacuum chamber has recently been developed as part of the Autonomous Vehicle Systems Laboratory at the University of Colorado Boulder. The experimental spacecraft charging research facility allows conducting experiments relevant to charged astrodynamics in a space-like environment. This paper discusses the development, characterization, and present capabilities of the vacuum chamber, which includes a range of sources to provide electron, ion, and photon fluxes, probes to characterize electron fluxes, x-rays, and potentials, and a variety of ancillary components to ensure the safe operation of the system, such as 3-axis motion stages, a magnetic environment control system, or a residual gas analyzer, among others. This state-of-the art facility has been used to conduct experiments on touchless spacecraft potential sensing, electrostatic actuation, or electron gun development, and will continue to be employed for the study of charged astrodynamics in the future. • ECLIPS is a vacuum chamber facility designed to study charged astrodynamics experimentally. • The motivation, design, and characterization of ECLIPS are presented. • Applications include research relevant to the electrostatic tractor concept or touchless spacecraft potential sensing. [ABSTRACT FROM AUTHOR]

Characteristics of annular electron flow formed in electron gun with a multitip field emitter were determined experimentally and by numerical simulations, and the possibility to achieve electron beam current up to 75 mA was demonstrated. The gun performance was stable in technical vacuum conditions—at the pressure of ~10−7 torr. Electron velocity distributions in a flow on transverse and longitudinal components were determined. It was shown that the relative root-mean-square transverse velocity spread varied with radial coordinate within the annular beam wall from ca. 6% to 30%, while the total spread in the electron flow was about 60%. [ABSTRACT FROM AUTHOR]

We present the design, simulation and analysis of 400 kW sheet beam gun. The beam optics, beam envelop and the magnetic field of the gun is designed and then simulated in CST PS. 100% beam transmission is achieved at the target similar to the size of the electron source. A space charge beam current of 5 A is obtained at 80 kV of acceleration voltage. Deformation calculated by the thermal analysis at 3000 °C temperature of the cathode has no significant effect on the electrodes. Besides metallurgical applications, the beam perveance 0.22 μP at 80 kV is useable for RF power amplification in klystron technology for linear accelerators. [ABSTRACT FROM AUTHOR]

This paper presents the design and fabrication of a reflex klystron oscillator based on a carbon nanotube (CNT) cold-cathode. An X-band klystron oscillator structure is assembled with a CNT cold-cathode electron gun with an electrostatic focusing, a re-entrant cavity as anode, and a repeller. The electron gun adopts a convex CNT film emitter as the cathode. A re-entrant cavity resonating at 8.376 GHz is fabricated. The study mainly focuses on the returning electron beam in the klystron oscillator structure. The experimental results of variations of the anode current and returning electron beam amplitude with repeller voltage are presented. It is demonstrated that a higher extracting voltage of the cold-cathode has an important influence on the returning electron beam. To decelerate electron velocity from the extracting voltage, increasing negative focusing voltage and focusing electrode height in the electron gun can improve the returning electron beam characteristics. [ABSTRACT FROM AUTHOR]

A new source of an electron beam with laser heating of the cathode is presented. The general description, the main parameters and the arrangement of the electron beam source are given. The cathode assembly and its operation features are described, which consist in controlling the emission current from the cathode by changing the cathode temperature by controlling the laser heating power. With this method, due to the heat capacity of the cathode and the parts nearby, the time to reach the set current level of the source from the moment the laser power is applied is several seconds. A method is proposed to reduce this time to fractions of a second by forcing the heating power at the beginning of turning on the heating and introducing preheating, and it is also proposed to stabilize the source current by introducing feedback of the heating power control signal with the current signal of the high-voltage source of the electron gun. The source current control range is discussed. [ABSTRACT FROM AUTHOR]

Tantalum oxide nanolayers of different thicknesses (30, 60, 90, and 120 nm) were deposited by physical evaporation on glass substrates at a deposition angle of 10° under high vacuum conditions at room temperature using an electron gun. There was no specific peak on the X-ray diffraction patterns because of amorphous nature of these layers. The results of atomic force microscopy showed that surface roughness reduced with increasing layer thickness. Field emission scanning electron microscopy images showed nucleation, growth, accession and integration as interconnected islands in the case of thinner layers and re-nucleation in the case of thicker ones (120 nm). Optical coefficients calculated using the Kramers–Kronig relations showed that with increasing layer thickness, dielectric properties, absorption coefficient, and band gap energy increased. [ABSTRACT FROM AUTHOR]

The electron beam quality of an electron gun is the key factor for the performance of vacuum electron devices. It is reported here that a convex carbon nanotube (CNT) emitter cathode is realized, improving the focus and laminar flow of the electron beam for a cold cathode gun. A mechanical polishing treatment was used to fabricate a convex shaped emitter of the cold cathode from vertically aligned CNTs, and it showed that the convex shaped emitter could effectively overcome the edge emission effect and improve the distribution uniformity. Also, the convex CNT cold cathode was utilized to fabricate a coaxial electron gun, and it presented that the beam spot of the gun is regular and uniform. Compared with the planar CNT emitter cathode, the convex emitter cathode demonstrated better uniformity and compatibility on the quality control of the electron beam. The present results indicate a viable route for improving the electron beam quality of nano-materials’ cold cathode gun. [ABSTRACT FROM AUTHOR]

In this article, the design and experiment of a hollow electron beam (HEB) electron optics system (EOS) for Ka-band extended interaction klystrons (EIKs) are presented. To realize the fast switch of the current emission at a low cutoff voltage, an electron gun with two focus electrodes (FEs) is chosen. The emitting surface of cathode is a ringed spherical surface. The first focus electrode (FE1) is around the cathode, and the second focus electrode (FE2) is set in the central hole of the cathode. The current emitted from the cathode surface is about 2A, when the operating voltage is 25 kV. Three simulation codes, Egun, Superfish, and CST, are used for designing the electron gun and the permanent magnet focusing system (PMFS). Some sensitivity analyses with respect to the PMFS’s critical parameters are presented. The simulation shows the dc beam transmission is 100%. The electron beam, confined by 6000 Gauss uniform field, propagates through the drift tube of 37 mm with good laminarity and small ripple. The emission current can be suppressed when the voltage of the FEs is −3.4 kV. According to the results of simulation, the Ka-band EIK had been constructed and the hot-test experiments had been fulfilled in succession. The experimental results exhibit that the dc beam transmission is about 99% and the beam can sustain 98% transmission at high frequency (HF) operation. In addition, the output power is higher than 8 kW in the bandwidth of over 100 MHz. [ABSTRACT FROM AUTHOR]

Field emission (FE) from semiconducting nanowires (NWs) is studied for expanding electron gun performances and functionality in terms of stability, brightness, and pulsed emission. Here, we report on a pronounced and robust double negative differential resistance (NDR) in the FE IV characteristics measured during photoassisted field emission experiments on highly crystalline p-type silicon NWs. The main feature is a double NDR in the current saturation regime, which can be modulated by both temperature and light intensity. These results contrast with previous FE studies in which only a barely noticeable single NDR was reported. Several mechanisms for the physical explanation of the NDR are currently under consideration: photogenerated carrier instabilities in the depletion region, which give rise to a pulsed space-charge current in the nanowire or tunneling through a double quantum well formed by confinement at the NW apex. Because NDRs are signatures of pulsed currents, these results suggest new functionalities for which pulsed electron sources can potentially be achieved at high repetition rates. [ABSTRACT FROM AUTHOR]

Summary: A traditional method for increasing the density of the optical films, is heating the substrate. An alternative way to increase the density of the film, is bombardment of substrate by ions during film growth. This method is known as ion assisted deposition (IAD). In this paper, magnesium fluoride, MgF2, thin film has been produced on a glass substrate by ion assisted deposition method. The effects of ion energy have been studied on density and refractive index film. Reflection, transmission and scattering spectra of the samples were measured by a spectrophotometer. Moreover, Atomic force microscope (AFM) is prepared. Using these measurements, optical and physical properties of the films are analyzed. A sample of MgF2 film has been produced without ion bombardment so that one can compare the effect of ion bombardment. [ABSTRACT FROM AUTHOR]

In the present article, a multi-cavity W-band gyro-twystron amplifier operating in fundamental TE01 mode has been designed, investigated for its beam-wave interaction behavior, and its performance has been enhanced by optimizing a diode type electron gun with a nominal velocity spread and stagger-tuning technique. The particle-in-cell simulation of the present gyro-twystron has predicted a peak RF output power of ~84 kW with a saturated gain of ~37 dB. The use of staggered RF cavities improved the bandwidth up to 1.5 GHz, which was found to be 2.5 times more than the synchronously tuned W-band gyro-twystron. The power conversion efficiency of the present stagger-tuned amplifier has been calculated as ~22%. A single anode magnetron injection gun has been designed and modeled to form the gyrating electron beam with 65 kV, 6 A, and 4% velocity spread by using 2-D electron optics code. A collector with an effective collecting area and an output window have been designed and studied to extract the remaining energy of spent electrons and collect the RF power from the vacuum environment, respectively. [ABSTRACT FROM AUTHOR]

Gyrotrons operating in high-order modes often suffer from severe mode competition. For the selective excitation of the desired mode, triode-type electron guns are often used. In the case of triode-type guns, where the beam voltage and the mod-anode voltage can be varied independently, the mode excitation during the startup process is studied in this article by using a generalized approach. The term “generalized approach” means that the obtained results can be valid for gyrotrons operating at arbitrary voltages and in any mode. The conditions for excitation of the modes are analyzed for different types of startup scenarios. The goal of the study is to find such relations between the beam and mod-anode voltages during the gyrotron startup that only the desired mode will be excited. It is shown that by using a specific triode-type startup scenario with a proper timing for the rise of the mod-anode voltage with respect to the beam voltage, the initial excitation of the desired mode can be realized in the cases of practically any mode density. The mode interaction in such a case is studied; also, the dependences of the results on the timing relation between the two voltages and on the voltage rise speed are considered. This article also contains the numerical analysis of a specific megawatt (MW) gyrotron with a triode-type gun. [ABSTRACT FROM AUTHOR]

Experiments have demonstrated high-power amplification (100 MW class) from a traveling wave amplifier driven by a modulated electron beam. The modulated electron beam is generated by applying a modulated voltage pulse from a nonlinear transmission line (NLTL) to the cathode of the electron gun. The system showed that over the designed operating range of the disk-on-rod (DoR) TWT amplifier (1.2–1.4 GHz), the peak frequency of the amplifier output tracked the peak frequency of the NLTL to within ±2%; however, the output was not phase stable. Measured RF energy gain for this frequency regime ranged from 1.5 at 1.2 GHz up to 5.0 at 1.4 GHz). [ABSTRACT FROM AUTHOR]