Search

The carbon nanotube cold cathode has important applications in the X-ray source, microwave tube, neutralizer, etc. In this study, the characteristics of carbon nanotube (CNT) electron gun in series with metal-oxide-semiconductor field-effect transistor (MOSFET) were studied. CNTs were prepared on a stainless steel substrate by chemical vapor deposition and assembled with a mesh gate to form an electron gun. The anode current of the electron gun can be accurately regulated by precisely controlling the MOSFET gate voltage in the subthreshold region from 1 to 40 µA. The current stability measurements show the cathode current fluctuation was 0.87% under 10 h continuous operation, and the corresponding anode current fluctuation was 2.3%. The result has demonstrated that the MOSFET can be applied for the precise control of the CNT electron gun and greatly improve current stability. [ABSTRACT FROM AUTHOR]

Temperature control is important in second harmonic generation (SHG) based on non-critical phase matching, which is widely used in the accelerator field to generate drive lasers. To further improve the stability of the drive laser for the DC-SRF photocathode electron gun at Peking University, a high-precision temperature control oven for lithium borate (LBO) crystals was developed. The oven's structure was designed to minimize heat exchange with the external environment. The temperature control circuit uses a thermoelectric cooler to ensure the temperature stability of the sampling circuit. The program utilizes a cascaded proportional-integral-derivative and an anti-saturation integral algorithm to achieve high-precision temperature control. Experiments showed that fluctuation at the working temperature of the LBO crystal in this oven was within ± 0.009 °C, corresponding to a root mean square (RMS) jitter of 0.003 °C, and the long-term power fluctuation of the 13.7 W green laser generated with SHG was less than 1%. [ABSTRACT FROM AUTHOR]

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We investigated electron emission characteristics of a hafnium carbide [HfC(100)] single-crystal tip at various temperatures toward finding a candidate of the next generation of emitters for electron microscopes. The emission mode changed from cold-field emission (CFE) to low-temperature and high-temperature thermal-field emission and, finally, to extended Schottky emission. The energy width at full width of half maximum of the emitted electrons was 0.2 eV in the CFE mode at an angular current of 20 μA/sr, and it showed good emission stability with current noise less than 3.5% in an electron gun of a scanning electron microscope (SEM). Spatial resolution of the SEM at an acceleration voltage of 0.5 kV improved 14% by using the HfC(100)-CFE tip instead of a conventional W(310)-CFE tip. High monochromaticity and stable electron emission of the HfC(100)-CFE tip are suitable for the next generation of emitters for ultrahigh-resolution field emission SEMs. [ABSTRACT FROM AUTHOR]

An electron gun that can produce MHz repetition rates and nanosecond pulses is described. The gun uses a Pierce grid in combination with an anode to extract electrons from a tungsten filament cathode. The electrons emerging from the anode are accelerated and focused using two triple-aperture lenses to form a beam. By applying a high slew rate grid pulse that transitions through the extraction voltage region of the grid/anode combination, pulses of electrons are produced from the gun that have temporal widths less than 5 ns. The pulsed beams are produced at both the rising and falling edges of the driving pulse. The characteristics of the emerging electron beams have been determined using an (e, 2e) coincidence spectrometer, and examples where they are used for time of flight decay measurements are presented. [ABSTRACT FROM AUTHOR]

Current day x-ray photoelectron spectroscopy (XPS) instrument makers have made significant advances in charge compensation systems over the last 20 years, which makes it easier to analyze insulators, but samples still have many differences in chemistry, dielectric properties, sizes, surface roughness, etc. that force instrument operators to tweak flood gun settings if they want or need to obtain high quality chemical state spectra that provide the most information. This guide teaches which flood gun variables to check, and how to optimize electron flood gun settings by presenting high energy resolution, chemical state spectra that show the result of using a poorly aligned flood gun on modern XPS instruments equipped with a monochromatic aluminum Kalpha x-ray source. This guide is focused on the XPS measurement of insulators—nonconductive metal oxides and polymers. This guide shows that by measuring commonly available polymers (polypropylene and polyethylene terephthalate) or ceramic materials (SiO2 and Al2O3), the operator can easily characterize the good and bad effects of XY position settings and other settings provided by modern electron flood gun systems. This guide includes many original, never-before-published XPS peak full width at half maximum (FWHM) that will greatly assist peak-fitting efforts. This guide reveals a direct correlation between electron count-rate and best charge-control settings. This guide discusses sample and instrument issues that affect surface charging and explains how to check the quality of charge control by measuring the FWHM and binding energy of C (1s) or O (1s) spectra produced from the sample currently being analyzed. A list of other charge-control methods is provided, along with advice and a best-known method. The availability of large extensive databases of actual spectra is extremely beneficial to users who need real-world examples of high quality chemical state spectra to guide their in-house efforts to collect high quality spectra and to interpret valuable information from the peak-fits of those spectra. [ABSTRACT FROM AUTHOR]

Low-emittance photoinjector-enabled cutting-edge scientific instruments, such as free-electron lasers, inverse Compton scattering light sources, and ultrafast electron diffraction, will greatly benefit from the improved repetition rate. In this paper, we proposed a specifically designed S-band radio frequency (RF) photoinjector to obtain low emittance and kilohertz (kHz) high-repetition rates simultaneously. By lowering the gradient, much lower RF power is needed to feed the electron gun, and then the heat problem is much easier to handle. Meanwhile, by optimizing the length of the gun's first cell from the normal case of 0.6-cell to 0.4-cell, the launch phase and the extraction field are significantly improved, thus ensuring the generation of low-emittance electron beams. In our design, the proposed 1.4-cell RF gun can work effectively under different field gradients ranging from 30 MV/m to 100 MV/m. For a standard case of 60 MV/m, 2.5 MW peak RF power with ys level pulse width is sufficient, thus offering the feasibility of improving the repetition rate to kHz level with a standard 5 MW irradiation klystron. In addition, simulated electron beams with a low emittance of 0.29 mm.mrad@200 pC can be generated by this proposed photoinjector, showing that this high-repetition rate injector holds the potential to deliver high-quality beams comparable to those of state-of-the-art S-band photoinjectors. Combining the merits of low emittance and high-repetition rate, this proposed photoinjector will provide a new possibility for future free-electron laser facilities operating at repetition rates ranging from kHz to tens of kHz. [ABSTRACT FROM AUTHOR]

A superradiant FEL in the THz (3 THz) region is currently operating at Ariel University. It is based on the novel ORGAD accelerator, which is a hybrid linear RF photo-cathode 6 MeV electron gun. The hybrid term stands for its unique standing wave (SW)—traveling wave (TW) structure. The undulator generates spontaneous superradiance, which corresponds to spontaneous emission when the electron bunch duration is shorter than the radiated frequency, resulting in a much higher photon yield. However, the efficiency of this scheme is still quite low. In order to achieve higher emission (by improved efficiency), we intend to implement a new and promising radiative interaction scheme: tapering-enhanced superradiance (TES). This particular undulator design employs a tapered (amplitude) undulator in the zero-slippage condition to obtain a significantly more powerful and efficient THz radiation source. At the current stage, the scheme is designed for emission at approximately 0.5 THz. The design and start-to-end simulations demonstrate significant enhancement of superradiant energy and extraction efficiency using this method compared to a reference uniform case. [ABSTRACT FROM AUTHOR]

The article discusses the various methods of estimating the surface cathode temperature of the high-voltage glow discharge electron gun, which forms a ribbon electron beam with a linear focus. Numerical estimations have been made to design the cathode assembly of an industrial gun. It is shown that the most effective way to make approximate estimates of the temperature of the cathode surface in high-voltage glow discharge electron guns for various technological purposes is to use arithmetic-logical ratios for modeling the geometry of the cathode assembly and locus functions for estimating the temperature distribution. The accuracy of such estimates, made using the heat balance equation, was 5–10%, sufficient at the initial stage of designing an electron gun. It is shown that using the SolidWorks CAD software complex for designing high-voltage glow discharge electron guns is effective only for solving the complex engineering design tasks and preparing the corresponding technical documentation. The results of the theoretical research published in the article are of interest to a wide range of specialists engaged in developing electron beam equipment and its implementation in industrial production. [ABSTRACT FROM AUTHOR]

The WCLL Breeding Blanket of DEMO and the Test Blanket Module (TBM) of ITER require accurate R&D activities, i.e., concept validation at a relevant scale and safety demonstrations. In view of this, the strategic objective of the Water Loop (WL) facility, belonging to the W-HYDRA experimental platform planned at C.R. Brasimone of ENEA, is twofold: to conduct R&D activities for the WCLL BB to validate design performances and to increase the technical maturity level for selection and validation phases, as well as to support the ITER WCLL Test Blanket System program. Basically, the Water Loop facility will have the capability to investigate the design features and performances of scaled-down or portions of breeding blanket components, as well as full-scale TBM mock-ups. It is a large-/medium-scale water coolant plant that will provide water coolant at high pressure and temperature. It is composed by single-phase primary (designed at 18.5 MPa and 350 °C) and secondary (designed at 2.5 MPa and 220 °C) systems thermally connected with a two-phase tertiary loop acting as an ultimate heat sink (designed at 6 bar and 80 °C). The primary loop has two main sources of power: an electrical heater up to about 1 MWe, installed in the cold side, downstream of the pump and upstream of the test section, and an electron beam gun acting as a heat flux generator. The WL has unique features and is designed as a multi-purpose facility capable of being coupled with the LIFUS5/Mod4 facility to study PbLi/water reaction at a large scale. This paper presents the status of the Water Loop facility, highlighting objectives, design features, and the analyses performed. [ABSTRACT FROM AUTHOR]

As the central component of the traveling wave tube (TWT), the thermal deformation of the electron gun is a critical concern. This paper presents a method for analyzing the electromagnetic characteristics of electron gun after thermal deformation. The method adopts multiple grid acceleration technology. Based on this method, a three-dimensional thermal stress analysis tool called the Thermal Stress Simulator (TSS) is developed. In addition, the TSS can be seamlessly coupled with the Thermal Simulator (TS) and the Electron Optical Simulator (EOS) previously developed by our team to realize the analysis of electromagnetic characteristics changes after thermal deformation and provide support for the reliable design of TWT. [ABSTRACT FROM AUTHOR]

Field emission electron probe microanalyzers (EPMA) and scanning electron microscopes (SEM) have improved in both the hardware and software. They have become workhorse instruments for imaging secondary (SE) and backscattered (BSE) electrons. Recent advancements in technology provide qualitative quantitative analysis and X-ray maps at lower kVs and higher beam current without significantly enlarging the beam diameter. On EPMAs and SEMs with W and LaB6 electron guns, spatial resolution for microanalysis was ∼1 micron. Now, with field emission (FE) guns, resolution of 300 nm for quantitative analysis and mapping of elements well below 100 nm are possible. Software has also become more user-friendly and has advanced automation algorithms that allow the "non-expert" EPMA user to collect data. However, the best part of automation sits in the user's chair. The new EPMAs and SEMs can collect very good data, but if they don't answer the question that is being asked, they have no use. [ABSTRACT FROM AUTHOR]

The carbon nanotube cold cathode has important applications in the X-ray source, microwave tube, neutralizer, etc. In this study, the characteristics of carbon nanotube (CNT) electron gun in series with metal-oxide-semiconductor field-effect transistor (MOSFET) were studied. CNTs were prepared on a stainless steel substrate by chemical vapor deposition and assembled with a mesh gate to form an electron gun. The anode current of the electron gun can be accurately regulated by precisely controlling the MOSFET gate voltage in the subthreshold region from 1 to 40 µA. The current stability measurements show the cathode current fluctuation was 0.87% under 10 h continuous operation, and the corresponding anode current fluctuation was 2.3%. The result has demonstrated that the MOSFET can be applied for the precise control of the CNT electron gun and greatly improve current stability.

Nowadays, by expanding the application of thin layers in industry and medical sciences, their fabrication methods have also received attention. One of those methods is the vaporizing material method with the help of an electron gun. The most important part in the electron gun is the electron optic, which is responsible for producing and accelerating electrons, so that it becomes possible to vaporize refractory materials in a shorter period of time by better modifying and controlling the electron beam (the shape and diameter of the electron beam) at the target location. The reduction and control of the beam diameter in this evaporation source depends on various parameters such as device geometry, magnetic field intensity, electric power, etc. Therefore, in this research, the effect of those parameters was investigated by conducting experiments and using finite element and modeling software. The simulation results revealed that the effect of the effective parameters on the beam diameter can be predicted to a good extent, so that the diameter of the electron beam decreases by changing the geometrical shape, size and displacement of the output beam components. Then, the new electron gun, compared to the existing prototype, is optimized by applying these changes in the construction of the device and conducting experiments, and its beam diameter is reduced by 40% to be more focused.

In this work, a Spindt cold cathode electron gun with a PPM (periodic permanent magnet) focusing system for a terahertz TWT (traveling wave tube) was designed and simulated based on the Pierce electron gun structure. More specifically, a new 3D (three dimensional) emission model was used, where the cathode radius of the electron gun was 1 mm and the cathode current was 30 mA, with an emitting half angle of about 28°. It was demonstrated that the electron beam was well focused with an electron beam radius of 0.3 mm and a filling ratio of 0.5 when the maximum value of the PPM field along with the axis was 0.122T. According to the simulation results, a planar cold cathode electron gun was developed. Measurements demonstrated that the I/V characteristics of the cold cathode gun were consistent with that of a cold cathode, revealing that the electrons emitted from the cathode are not intercepted when passing through the electron gun. [ABSTRACT FROM AUTHOR]

A test-Accelerator as Coherent Terahertz Source (t-ACTS) has been under development at Tohoku University, in which an intense coherent terahertz radiation is generated from the short electron bunches. Velocity bunching scheme in a traveling wave accelerating structure is employed to generate the short electron bunches. The in-phase and quadrature (IQ) modulator and demodulator were installed to the low-level RF systems of t-ACTS linac to control and measure the amplitude and phase of RF power. The amplitude and phase of the RF power applied to an RF electron gun cavities and the accelerating structure are controlled to produce the electron bunches with a uniform and small momentum spread suitable for the velocity bunching. By installing the feed-forward control system using IQ modulators for the beam conditioning, we have successfully generated flat RF pulses and improved beam quality, including the energy spectrum of the beam. The details of feed-forward control system of the amplitude and phase using the IQ modulator and the beam experiments are presented in this paper. [ABSTRACT FROM AUTHOR]

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

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]

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]

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]

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]

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.

• 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]

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.

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]

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 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]

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]

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]

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]

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]

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]

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]

A new approach to realization of a high cyclotron harmonic gyro-oscillator based on the frequency multiplication effect is proposed and numerically studied. This approach utilizes axially asymmetric electron beam optics, which nevertheless may be as simple as the one of the conventional gyrotrons. Numerical simulations show that the proposed method can provide a watt-level output power in THz and sub-THz frequency ranges using existing electron guns. [ABSTRACT FROM AUTHOR]

To improve the performance of a pencil beam electron gun for terahertz traveling wave tubes (TWT), a support vector regression (SVR) method combined with a goal attainment algorithm, which is used to optimize its structural parameters considering the periodic permanent magnetic (PPM) focusing system, is proposed in this article. Moreover, a parameter correction method to reduce the impact of the thermal expansion on the electron gun is proposed. An electron gun for 0.22-THz TWT gun is developed, in which a 30-mA/23.8-kV electron beam emitted by a curved barium–tungsten cathode with a beam loading of 4 A/cm2 is achieved with the optimized parameters. To the high current density for THz beam–wave interaction, the area compression ratio of electron beam is used in beam tunnel and reaches 144. The experimental results are very similar to the simulation results, which indicate that the methods would be beneficial to the development of TWT. [ABSTRACT FROM AUTHOR]

A novel electron-optical system (EOS) for ${G}$ -band traveling-wave tubes (TWT) is investigated by simulation and verified by experiment. The EOS includes a sheet beam electron gun, a tunable periodic cusped magnetic focusing (TPCMF), and a collector. An elliptical focus electrode (FE) featuring a simple geometry and easy fabrication is utilized to compress the pencil beam into the sheet beam with a cross section of 0.4 mm $\times0.1$ mm. The electron gun with a cylindrical cathode of 0.8 mm diameter generates the sheet beam with voltage of 22 kV and current of 115 mA. Based on the sheet beam electron gun, the TPCMF with easy assembly and compact size is then proposed. The experimental results show that the beam transmission is 92.1% within a beam tunnel (its length 21.2 mm and cross section 0.8 mm $\times0.15$ mm). The EOS is suitable for ${G}$ -band TWT. [ABSTRACT FROM AUTHOR]

Using Auger electron spectroscopy, an experimental study of the Si – Cr – Ni system was carried out. A comparative analysis of the results before and after exposure to thermal shock at the interfaces showed the effect of temperature on the distribution of elements over the thickness of the deposited layers. An increase in the number of thermal shocks leads to the fact that nickel remains on the surface of the silicon substrate, and chromium diffuses into silicon.

This paper presents the design of a thermionic electron gun with two different geometries, flat cathode and spherical cathode.The purpose of this research is to answer the question of which type of electron gun is suitable for industrial electrostatic accelerators. CST Studio software was used to design the guns. The desired specification in the design of a suitable thermionic gun, the maximum current of 50 milliamper and the voltage 5 to 10 kilovolt, is selected for use in the dynamitron accelerator. The beam current, the waist beam radius, the waist beam position and the perveance of a flat cathode gun and spherical cathode gun were 49 and 49.8 mA, 3.2 and 0.45 mm, 36 and 24.3mm, 0.138 and 0.0498 μperv, respectively. Since the electron guns used in the industry have a perveance between 0.1 to 1 μperv therefore, an electron gun with a flat cathode with 0.138 μperv is more suitable. On the other hand, it is easier and less costly to make it. That is why the gun with a flat cathode was chosen and its final dimensions are presented.

The need for enhanced performance of high-power RF vacuum electron devices has led to the investigation of multiple-beam, sheet beam, and annular beam configurations. A key issue with such devices is the magnetic field shaping required producing high-power, laminar beams. Field shaping is difficult when Pierce-type gun geometries are employed. The development of high current density cathodes makes the necessary beam power achievable without compression. Such cathodes can operate within a uniform magnetic field yielding advantages for both single and distributed-beam RF devices. However, the quality of the resulting beams presents problems. A project to optimize beam quality in zero-convergence electron guns was undertaken by Calabazas Creek Research, Inc. (CCR) and North Carolina State University (NCSU). The surprising result was that high-quality electron beams can be generated in uniform magnetic fields using convex (dome)-shaped cathodes. The underlying physics involves perturbation of the beam cyclotron motion by a nonadiabatic radial electric field impulse. This article examines this physical mechanism and extends the initial result to additional diode and beam geometries. [ABSTRACT FROM AUTHOR]

Ubiquitous wireless distribution of multigigabit per second data rate for enabling new 5G and 6G paradigms can be only achieved by exploiting the wide frequency bands available in the sub-THz spectrum (90–305 GHz). The high total attenuation at sub-THz, in particular because of rain and humidity, poses a substantial challenge to achieve long links, not yet resolved because of the lack of amplifiers with adequate transmission power. Sub-THz traveling wave tubes (TWTs) are emerging as key components to ensure high signal-to-noise ratio over a large coverage area or for long distance. This article will describe the design and fabrication of a novel TWT for enabling point to multipoint wireless distribution at ${D}$ -band (141–148.5 GHz). To be suitable for the wireless market, TWTs need to be low cost and easily manufacturable for large-scale production. The proposed ${D}$ -band TWT uses a double corrugated waveguide as slow wave structure and a new electron gun, both designed for easy assembly and low fabrication cost. This article describes the design process, the development of the parts of the TWT, and the first prototype assembly. [ABSTRACT FROM AUTHOR]

The electron beam of a K-band space traveling-wave tube (TWT) has been investigated in a beam measurement system in this article. The primary beam emitted from a Pierce-type electron gun is scanned by a Faraday cup probe, and the beam current density distribution and envelope are determined. The spent beam is also diagnosed with a novel retarding field energy analyzer (RFEA) by using the monopulse measurement method, and a comparison of velocity distribution between the experimental result and simulation is presented. [ABSTRACT FROM AUTHOR]

In this article, a trigger unit has been implemented to generate a high-current-density electron beam from a pseudospark (PS) discharge-based electron gun. A trigger pulse power supply unit has been designed and developed to provide the seed electrons from the ferroelectric cathode (FEC). The FEC has been used inside the hollow cathode cavity of a single-gap PS discharge-based electron gun. The electron gun has been operated in the self-breakdown as well as the trigger-based breakdown mode. A comparative analysis has also been performed between self-breakdown and trigger breakdown modes with the developed trigger unit’s help for different applied gap voltages ranging between 0 and 16 kV. The designed trigger unit is based on a high-voltage-gain isolated dc–dc converter and a pulse-forming network. It is compact and capable of generating a negative pulse of ~–5 kV with a pulsewidth of ~500 ns. It provides better control over PS discharge to produce a high-current-density electron beam. [ABSTRACT FROM AUTHOR]

Nanosecond pulse output at megahertz level is wide interest because of its potential application in the experiment of cell function electric field regulation and accelerator electron gun injector. In this article, a pulse generator based on the combination of the Blumlein pulse forming line and the boost method is proposed. Different from the traditional Blumlein line, in this module, the RLC circuit is used to improve the pulse voltage amplitude and energy conversion efficiency. According to the different inductance values, the generator has two working modes: discontinuous and continuous with different output characteristics. RF-Si-mosfet is used as the main switch and used dual-switch timing logic control to adjust the output waveform parameters. It can obtain the output pulse frequency two times the switching frequency, effectively reducing the single switching loss. By constructing a prototype, the pulsewidth of 5 ns, maximum repetition of 10 MHz and 2.5-kW peak power is realized. In addition, a dc equivalent pulse method is proposed, which is suitable for the thermal simulation of switching at high frequency and gives the heat dissipation measures. The effectiveness is verified by simulation and experiment. [ABSTRACT FROM AUTHOR]