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Generation of THz radiation based on the Smith-Purcell effect in graphene is investigated numerically. The specific device geometry considered involves an electrically biased single-layer sheet of graphene deposited on a periodic array of holes in a solid substrate. Rigorous electrodynamic simulations combined with a basic model of charge transport are presented, showing that technologically signifcant output power levels can be obtained at geometrically tunable THz frequencies. These results suggest that graphene is a uniquely suited materials platform for the demonstration of THz electron-beam radiation mechanisms in compact solid-state systems. [ABSTRACT FROM AUTHOR]

The RF properties of an accelerating structure, and the pulse structure and charge per bunch in the electron beam propagating through it are important parameters that determine the impact of beam loading in the structure. The injector linac of the Compact Ultrafast Terahertz Free-Electron Laser (CUTE-FEL) has been operated with two different pulse structures during initial commissioning experiments and the effect of beam loading on the accelerated electron beam parameters has been studied analytically for these two pulse structures. This paper discusses the analytical study of beam loading in a Standing Wave, Plane Wave Transformer linac employed in the CUTE-FEL setup, and a possible technique for its compensation for the electron beam parameters of the CUTE-FEL. A parametric study has been performed to study beam loading for different beam currents and to optimize injection time of the electron beam to compensate beam loading. Results from the parametric study have also been used to explain previously observed results from acceleration experiments in the CUTE-FEL setup. [ABSTRACT FROM AUTHOR]

In this paper, a wideband 220-GHz sheet-beam traveling-wave tube (TWT) based on staggered double vane slow-wave structure (SWS) is investigated. A novel method of loading the attenuator into the SWS for suppressing backward wave oscillation is proposed. In addition, a novel focusing electrode of the sheet beam gun is carried out in this paper, which is a whole structure but divided into two parts artificially, one is used to compress the electron beam in $X$ -direction and the other is used to compress the electron beam in $Y$ -direction. In addition, a novel anode is redesigned to reduce the defocusing effect caused by the equipotential surfaces. A nonuniform periodically cusped magnet is used for focusing the sheet electron beam, which is predicted to exhibit 100% beam transmission efficiency in a 75-mm length drift tube. The high-frequency characteristics of the SWS and the beam-wave interaction are also studied. The results reveal that the designed TWT is expected to generate over 78.125-W average power at 214 GHz, and the 3-dB bandwidth is 31.5 GHz, ranging from 203 to 234.5 GHz. [ABSTRACT FROM PUBLISHER]

Upon the interaction of 60 TW Ti: sapphire laser pulses with 4 mm long supersonic nitrogen gas jet, a directional x-ray emission was generated along with the generation of stable quasi-monoenergetic electron beams having a peak energy of 130 MeV and a relative energy spread of ~ 20%. The betatron x-ray emission had a small divergence of 7.5 mrad and a critical energy of 4keV. The laser wakefield acceleration process was stimulated in a background plasma density of merely 5.4 x 1017cm-3 utilizing ionization injection. The non-self-focusing and stable propagation of the laser pulse in the pure nitrogen gaseous plasma should be responsible for the simultaneous generation of the high-quality X-ray and electron beams. Those ultra-short and naturally-synchronized beams could be applicable to ultrafast pump-probe experiments. [ABSTRACT FROM AUTHOR]

We report selective area growth of large area homogeneous Bernal stacked bilayer epitaxial graphene (BLEG) on 4H-SiC (0001) substrate by electron-beam irradiation. Sublimation of Si occurs by energetic electron irradiations on SiC surface via breaking of Si-C bonds in the localized region, which allows the selective growth of graphene. Raman measurements ensure the formation of homogeneous BLEG with weak compressive strain of -0.08%. The carrier mobility of large area BLEG is ~5100 cm² V-1 s-1 with a sheet carrier density of 2.2 x 1013 cm-2. Current-voltage measurements reveal that BLEG on 4H-SiC forms a Schottky junction with an operation at mA level. Our study reveals that the barrier height at the Schottky junction is low (~0.58 eV) due to the Fermi-level pinning above the Dirac point. [ABSTRACT FROM AUTHOR]

Electron Beam Induced Current (EBIC) measurements were used to produce cross sectional images of superjunction power transistors. These images show how the depletion width expands under reverse bias. Superjunctions are alternating p- and n-type doped vertical columns placed between drain and source in a power transistor (Deboy et al., in: Proc. IEDM, 983-685 (1998); Lorenz et al., in: Proc. PCIM Europe, 250-258 (1998)). These columns allow a higher substrate doping of the drift region, resulting in a lower on-state resistance while still maintaining a high breakdown voltage. When the device is reverse biased, the space charge region of the superjunction should expand symmetrically due to the homogeneous doping (in the n and p region) until the complete device depletes. The depletion process was also visualized using voltage contrast (VC) measurements. Here the secondary electron signal was detected when the device was reverse biased. We show that EBIC and VC measurements can provide valuable input for process tuning and process simulations, enabling the use of smaller dimensions and higher doping levels [ABSTRACT FROM AUTHOR]

Proton (H+) implantations are used in power semiconductor devices to introduce recombination centers (Hazdra et al., Microelectron. J. 32(5), 449-456 (2001)) or to form hydrogen related donor complexes (Zohta et al., Jpn. J. Appl. Phys. 10, 532-533 (1991)). Proton implantations are also used in the 'smart cut' process to generate defects that can be used to cleave thin wafers (Romani and Evans, Nucl. Instrum. Methods Phys. Res. B 44, 313-317 (1990)). However, the implantation damage resulting from H+implantations is not completely understood. In this study, protons with energies from 400 keV up to 4 MeV and doses up to 1016 H+/cm² were implanted into highly ohmic boron doped m:Cz silicon (100). Electron Beam Induced Current (EBIC) measurements were performed to locally determine the minority charge carrier diffusion length. The diffusion length decreases with increasing implantation dose and incorporated damage. Spreading Resistance Profiling (SRP) measurements were performed to analyze the charge carrier concentration profiles for different annealing procedures. The electrical activation and growth of the defect complexes varies strongly with the annealing parameters. Transmission Electron Microscopy measurements were made to investigate the microscopic structures formed by the high dose implantation processes. Due to the high local damage density resulting from low energy and high dose H+ implants, platelet structures are formed. During high-energy high-dose H+implantations, the implanted hydrogen generates strain in the crystal lattice resulting in changes in the distances between atomic planes. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Based on numerical simulation, a scheme of the \(X\) -band relativistic Cherenkov microwave oscillator with a hollow cylindrical increased cross-sectional electron beam transported by the external magnetic field is considered. For the electron energy of \(\sim 0.5\) MeV and electron beamwidth of \(\sim 5\) mm, an effective 100-ns-long pulse mode in a reduced magnetic field of 0.75 T has been calculated. Within the stationary stage of oscillation, the maximum simulated microwave power for the operating TM01 mode was 630 MW that corresponded to the oscillator efficiency of 34% at the oscillation frequency of 10 GHz. [ABSTRACT FROM PUBLISHER]

A series of nylon 6-clay nanocomposites were prepared by melt mixing, followed by electron beam (EB) crosslinking at various doses. Effects of crosslinking on clay dispersion, gel content, crystallinity and water absorption properties (hygrothermal) were studied. No change of the dispersion pattern of clay in nanocomposites was observed after crosslinking [from X-ray diffraction (XRD) and transmission electron microscopy (TEM)]. Gel content, i.e., degree of crosslinking is seen to keep on increasing with irradiation dose, although clays hinder crosslinking of polymers to some extent. Crystallinity of polymers is reduced after incorporation of clay as well as crosslinks. However, water absorption rate and maximum water content of nanocomposites are found to increase and saturation time to decrease with clay content. However, these changes become opposite after crosslinking of polymers. The water absorption for all samples is noticed to increase with temperature. Thus, EB crosslinking, without affecting the nanocomposite morphology, i.e., properties derived from nano interface generation, decreases the water absorption properties of nanocomposites. [ABSTRACT FROM AUTHOR]

Moiré method in scanning transmission electron microscopy allows observing a magnified two-dimensional atomic column elemental map of a higher pixel resolution with a lower electron dose unlike conventional atomic column mapping. The magnification of the map is determined by the ratio between the pixel size and the lattice spacing. With proper ratios for the x and y directions, we could observe magnified elemental maps, homothetic to the atomic arrangement in the sample of SrTiO3 [0 0 1]. The map showed peaks at all expected oxygen sites in SrTiO3 [0 0 1]. [ABSTRACT FROM PUBLISHER]

Cube-shaped IN718 samples were produced by selective electron beam melting (SEBM) with varying beam power, deflection speed, and beam spot size. Process parameter windows were identified where fully dense samples are obtained with no surface unevenness. High deflection speeds were demonstrated to result in smaller demand of area energy. This result is explained by the reduced time for heat dissipation into the substrate during hatching. The grain structure was strongly affected by SEBM process parameters. Under certain conditions, epitaxial growth over many layers and well-developed columnar grain structures were obtained with a polycrystalline substrate plate. A more defocused beam led to a lower melt pool temperature and shallower melt pool geometry where maximum temperature gradients and solidification rates were more or less in parallel with the building direction and primary dendrite arm orientation. These conditions help to suppress grain nucleation ahead of the nucleation front as vigorous melt movement, fragmentation of dendrites, and tertiary arm growth are suppressed. [ABSTRACT FROM PUBLISHER]

The effect of the beam scanning speed on part microstructures in the powder-bed electron beam additive manufacturing (EBAM) process was investigated in this research. Four levels of the beam speed were tested in building EBAM Ti–6Al–4V samples. The samples were subsequently used to prepare metallographic specimens for observations by optical microscopy and scanning electron microscopy. During the experiment, a near-infrared thermal imager was also used to acquire build surface temperatures for melt tool size estimates. It was found that the X-plane (side surface) shows columnar prior β grains, with the width in the range of about 40–110 µm, and martensitic structures. The width of columnar grains decreases with the increase of the scanning speed. In addition, the Z-plane (scanning surface) shows equiaxed grains, in the range of 50–85 µm. The grain size from the lowest beam speed (214 mm/s) is much larger compared to other samples of higher beam speeds (e.g., 376–689 mm/s). In addition, increasing the beam scanning speed will also result in finer α-lath. However, the porosity defect on the build surface also becomes severe at the highest scanning speed (689 mm/s). [ABSTRACT FROM PUBLISHER]

In this letter we study the influence of temperature and excitation power on the emission linewidth from site-controlled InGaAs/GaAs quantum dots grown on nanoholes defined by electron beam lithography and wet chemical etching. We identify thermal electron activation as well as direct exciton loss as the dominant intensity quenching channels. Additionally, we carefully analyze the effects of optical and acoustic phonons as well as close-by defects on the emission linewidth by means of temperature and power dependent micro-photoluminescence on single quantum dots with large pitches. [ABSTRACT FROM AUTHOR]

We demonstrate that under continuous single-beam excitation, one can generate an abnormal anti-Stokes Raman emission (AASRE) whose properties are similar to a coherent anti-Stokes Raman scattering. The effect has been observed in mesoscopic materials, which possess intrinsically nonlinear properties [lithium niobate (LiNbO3), bismuth germanium oxide (Bi12GeO20; BGO), bismuth silicon oxide (Bi12GeO20; BSO)], which have a nonzero electric susceptibility of the third order, χ(³) ≠ 0. Corroborated Raman and coherent backscattering studies demonstrate that the occurrence of both effects is conditioned by the existence of a mesoscopic morphology of the sample, which is able to ensure efficient transport of the light inside the sample through a multiple light scattering mechanism. In this context, both AASRE and coherent backscattering effects are because of the Anderson localization of the light. [ABSTRACT FROM AUTHOR]

The performance of the electromagnetic wave with power of over 100 kW at 0.4 THz is very attractive in plasma diagnostics; the 0.4 THz second harmonic gyrotron is strict with the quality of the electron beam. The quality model of the electron beam is built in practical engineering in this paper. Based on the self-consistent nonlinear beam-wave interaction theory for gyrotrons, the relationship among the quality of the electron beam, the performance of the terahertz gyrotron from the aspects of the orbital-to-axial velocity ratio, the guiding center radius, the spread of the velocity, and the thickness of the electron beam of the designed gyrotron is studied. The results show that the gyrotron is insensitive to the voltage and current of the electron beam in a wide range, and sensitive to the orbital-to-axial velocity ratio and the guiding center radius of the electron beam. The efficiency decreases when the electron beam spread is deepening, and the deepening has a little improvement when both guiding center and velocity spreads are involved in the beam-wave interaction. [ABSTRACT FROM PUBLISHER]

Present work deals with the study of luminescence and structural properties of Y-doped ZrO2 nanopowders sintered by co-precipitation of Zr and Y nitrates. The structural and light emitting properties were controlled by X-ray diffraction, transmission electron microscopy, Raman scattering, photo- (PL) and cathodoluminescence (CL) methods. Generally, room temperature PL spectra showed several bands in UV-orange range, whose shapes depend on the excitation light wavelength. Along with this, CL spectra demonstrate additional 'red' emission, which intensity exceeds that of other CL bands. At lower temperatures, preferable enhancement of 'red' CL band, its narrowing and peak position shift to the longer wavelengths were found. This behavior testifies to the non-elementary nature of 'red' CL band. Its nature and mechanism of its excitation are discussed. It is supposed that some impurities (such as Fe and/or Zn) or complex defects, containing oxygen vacancies and these impurities, are responsible for 'red' emission appeared under electron beam excitation only. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Silica nanowires were synthesized from mixture monosilane with hydrogen by gas-jet electron beam plasma chemical vapor deposition method for the first time. The synthesis was carried out on silicon substrate with up to micrometer-sized particles of Sn catalyst. SEM observations show that this method provides different morphology of the nanowires and catalyst. Oriented arrays of silica nanowires bunches (microropes) were synthesized in the area corresponding to the mixture jet axis. Cocoons-like, bamboo-like, and jellyfish-like morphology was observed in the area corresponding to periphery of the jet. Probably there was realised vapor-liquid-solid (VLS) growth mechanism, where multiple nanowires grow simultaneously from the surface of one catalyst drop. The growth rate of the microropes is about 25 nm/s at synthesis temperature 330 °C. Possible growth model has been suggested in order to explain the results. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Along with the dose rate and the total irradiation dose measurements, the knowledge of the beam localization and the beam profile/energy distribution in the beam are parameters of interest for charged particle accelerator installations when they are used in scientific investigations, industrial applications or medical treatments. The transverse profile of the beam, its position, its centroid location, and its focus or flatness depend on the instrument operating conditions or on the beam exit setup. Proof-of-concept of a new type of charged particle beam diagnostics based on fiber Bragg gratings (FBGs) was demonstrated. Its operating principle relies on the measurement of the peak wavelength changes for an array of FBG sensors as function of the temperature following the exposure to an electron beam. Periodically, the sensor irradiation is stopped and the FBG are force cooled to a reference temperature with which the temperature influencing each sensor during beam exposure is compared. Commercially available FBGs, and FBGs written in radiation resistant optical fibers, were tested under electron beam irradiation in order to study their possible use in this application. [ABSTRACT FROM AUTHOR]

Electron beam-induced nanoinstabilities of pristine double-walled carbon nanotubes (DWCNTs) of two different configurations, one fixed at both ends and another fixed at only one end, were in-situ investigated in transmission electron microscope at room temperature. It was observed that the DWCNT fixed at both ends shrank in its diameter uniformly. Meanwhile, the DWCNT fixed at only one end intriguingly shrank preferentially from its free cap end along its axial direction whereas its diameter shrinkage was offset. A mechanism of "diffusion" along with "evaporation" at room temperature which is driven by the nanocurvature of the DWCNTs, and the athermal activation induced by the electron beam was proposed to elucidate the observed phenomena. The effect of the interlayer interaction of the DWCNTs was also discussed. [ABSTRACT FROM AUTHOR]

Single nanoantenna spectroscopy was carried out on realistic dipole nanoantennas with various arm lengths and gap sizes fabricated by electron-beam lithography. A significant difference in resonance wavelength between realistic and ideal nanoantennas was found by comparing their spectral response. Consequently, the spectral tunability (96 nm) of the structures was significantly lower than that of simulated ideal nanoantennas. These observations, attributed to the nanofabrication process, are related to imperfections in the geometry, added metal adhesion layer, and shape modifications, which are analyzed in this work. Our results provide important information for the design of dipole nanoantennas clarifying the role of the structural modifications on the resonance spectra, as supported by calculations. [ABSTRACT FROM AUTHOR]

A series of experiments on small aspect ratio rod pinches using solid tungsten, solid graphite, and thin-wall tantalum anode rods driven by a nominally 375-kV linear transformer driver, powered inductive voltage adder has characterized the impedance behavior over a range of aspect ratios and materials. For the tungsten and tantalum anodes, the impedance behavior is well described by the pinched current for self-magnetically insulated flow in a cylindrical geometry with ions present and gap closure velocities of 1–2 cm/ \(\mu \) s. The graphite anodes always exhibited strong localized pinching of the electron beam onto the anode rod, with substantially higher operating impedance, as well as a delay in the formation of the plasma at the anode. The graphite anodes also had a longer radiation delay time, consistent with the longer anode plasma formation time. [ABSTRACT FROM PUBLISHER]

The high-impedance relativistic klystron based on the hot cathode, of high power, long pulse, high efficiency and stable amplitude and phase, is one of the promising candidates for the high-power microwave coherent power combing. As a high-quality, small radius electron beam plays a crucial role in an effective beam-wave interaction, a high-convergence electron optics system is required for an 11.424GHz high-impedance relativistic klystron, with an output power of 105MW. In the design, to alleviate the cathode loading due to high-convergence, the uniformity of the cathode emittance and the laminarity of beam are both sacrificed. Then serious space charge effect is likely to occur with a rather high current density. To minimize the scalloping, it is difficult to provide the best overlap of the beam trajectories and magnetic force lines with priority to the amplitude of magnetic flux at the cathode. With the synthesis of Pierce's electron gun and the cylindrical focusing electrode, a particle in cell model of the electron gun is constructed to obtain the electrostatic characteristics of the electron beam. Based on the electrostatic beam trajectories, a beam-focusing system is designed, with which electron beam can be well focused by adjusting the magnetic field profile especially in the transient region. The PIC simulation results indicate that the balance radius of the reasonably fluctuated beam is about 3mm,with a fine laminarity, and the transmission, the perveance and the area convergence are 100%, 0.9 µP and 97 : 1 respectively, which satisfy the requirement of the 11.424GHz high- impedance relativistic klystron. Moreover, with the comparison between thermionic emission and explosive emission in PIC code, the micro-characteristics of beam shows the latter is tend to be more reliable. [ABSTRACT FROM AUTHOR]

Based on the theoretical analysis of the intense relativistic electron beam propagation in the coaxial drift-tube, a focusing electrode and a coaxial reflector is proposed to lessen the demand of the coaxial Ku-band foilless transit-time oscillator (TTO) for the guiding magnetic field. Moreover, a Ku-band TTO with the focusing electrode and the coaxial reflector is designed and studied by particle in cell simulation. When the diode voltage is 390 kV, the beam current 7.8 kA, and the guiding magnetic field is only 0.3 T, the device can output 820 MW microwave pulse at 14.25 GHz by means of the simulation. However, for the device without them, the output power is only 320 MW. The primary experiments are also carried out. When the guiding magnetic field is 0.3 T, the output power of the device with the focusing electrode and the coaxial reflector is double that of the one without them. The simulation and experimental results prove that the focusing electrode and the coaxial reflector are effective on reducing the guiding magnetic field of the device. [ABSTRACT FROM AUTHOR]

Uniform and monodisperse Gd(OH)3:Eu3+ hexagonal prisms were successfully synthesized at mild conditions via a large-scale and facile homogeneous coprecipitation process without using any catalysts, surfactants or templates. The size of the as-formed Gd(OH)3:Eu3+ precursor prisms could be modulated from the micro- to nanoscale by the use of urea and changing the pH values of the initial solutions. A possible formation mechanism for the Gd(OH) 3:Eu3+ hexagonal nano-/microprisms was proposed. After a postannealing process, Gd2O3:Eu3+ hexagonal nano-/microprism phosphors with a slight shrinking in size can be transformed from Gd(OH)3:Eu3+. Both the Gd3O3:Eu3+ nanoprisms and microprisms exhibit the same strong red emission corresponding to the 5 D0 → 7 F2 transition (610 nm) of Eu3+ under UV light excitation (243 nm) and low-voltage electron beam excitation (1-6 kV). Furthermore, the experimental results indicate that the luminescence properties of the as-obtained phosphors are dependent on their morphologies and sizes. As a result of the controllable morphology and size, and excellent luminescence properties, these Gd3O3:Eu3+ nano-/microprism phosphors may find potential applications in optoelectronic devices (fluorescent lamps and field emission displays), bioanalysis and biomedical areas and so on. [ABSTRACT FROM AUTHOR]

We demonstrate the dual-band operation of a relativistic backward wave oscillator (RBWO) whose output is a linearly polarized TE \(_{\mathrm {\mathbf {11}}}\) -mode. The RBWO consists of two cylindrical sections with sinusoidal corrugations where the downstream section is axisymmetric and the upstream section has combined left- and right-single-fold spiral corrugations. We show that generation of 10 GHz is realized when the axisymmetric section operates as a BWO with the operating TM \(_{\mathrm {\mathbf {01}}}\) -mode and the combined spiral section operates as a Bragg reflector that converts the backward TM \(_{\mathrm {\mathbf {01}}}\) -mode to a linearly polarized forward TE \(_{\mathrm {\mathbf {11}}}\) -mode. For the same electron beam parameters, generation of 7 GHz is realized when the combined spiral section operates as a BWO with the operating TE \(_{\mathrm {\mathbf {11}}}\) -mode. We also present the possibility to change the duration of generation at each frequency within a microwave pulse by changing the electron beam current. In addition, one can change the output frequency by changing the values of the guide magnetic field near the region of cyclotron absorption. [ABSTRACT FROM PUBLISHER]

In a first study to analyze the feasibility of electron beam-induced deposition (EBID) for creating certain patterns in advanced lithography, line patterns were fabricated on silicon wafers using EBID. The growth conditions were such that the growth rate is fully determined by the electron flux (the current limited growth regime). It is experimentally verified that different patterning strategies, such as serial versus parallel patterning and single pass patterning versus multiple pass patterning, all lead to the same result in this growth regime. Images of EBID lines, imaged in a scanning electron microscope, were analyzed to determine the position of the lines, the width of the lines, and the linewidth roughness (LWR). The results are that the lines have an average width of 13.7 nm, an average standard deviation of 1.6 nm in the center position of the lines, and an average LWR of 4.5 nm (1s value). As an example of the capabilities of EBID, a logic-resembling lithography pattern was fabricated. [ABSTRACT FROM AUTHOR]

High chemical resistance is the main prerequisites for materials that are intended to be utilized in usages such as chemicals storage containers production. Nanocomposites of epoxy resin containing nanoclay, CaCO and TiO nanoparticles were prepared and their chemical resistance was studied. Moreover, the effect of electron beam irradiation was explored. TEM micrographs proved the dispersion of nano-size particles in the polymeric matrix. XRD patterns showed an exfoliated structure for nanocomposite containing 1 % nanoclay and intercalated structures for nanocomposites with higher nanoclay contents. SEM showed the pits that appeared in epoxy/nanoclay structure due to chemical corrosion. Weight loss measurements revealed that an addition of 1 % nanoclay to the epoxy matrix is effective for improving the chemical properties of the polymer. Desirable effect of 100 kGy irradiation on chemical resistance properties of the samples was also observed in both acidic and basic environments. [ABSTRACT FROM AUTHOR]

The Electron Beam Ion Trap (EBIT) of the National Superconducting Cyclotron Laboratory at Michigan State University is used as a charge booster and injector for the currently commissioned rare isotope re-accelerator facility ReA. This EBIT charge breeder is equipped with a unique superconducting magnet configuration, a combination of a solenoid and a pair of Helmholtz coils, allowing for a direct observation of the ion cloud while maintaining the advantages of a long ion trapping region. The current density of its electron beam is a key factor for efficient capture and fast charge breeding of continuously injected, short-lived isotope beams. It depends on the radius of the magnetically compressed electron beam. This radius is measured by imaging the highly charged ion cloud trapped within the electron beam with a pinhole camera, which is sensitive to X-rays emitted by the ions with photon energies between 2 keV and 10 keV. The 80%-radius of a cylindrical 800 mA electron beam with an energy of 15 keV is determined to be r80% = (212 ± 19)μm in a 4 T magnetic field. From this, a current density of j = (454 ± 83)A/cm² is derived. These results are in good agreement with electron beam trajectory simulations performed with TriComp and serve as a test for future electron gun design developments. [ABSTRACT FROM AUTHOR]

A new kind of radial convergent sheet beam electron optical system, which can be used in low voltage Ka-band radial electron devices, is studied in this paper, including the beam production, transmission, and focus. A novel radial high perveance electron gun is proposed, and its volt-ampere characteristics are obtained by means of simulation. The focusing system using permanent magnet rings is put forward, by which a radial uniform magnetic field can be obtained. With the electron gun and focusing system, a 1600 V, 8 A, and 0.04-mm thickness radial convergent sheet beam was produced, and the simulation result shown that it can pass through a 16-mm \(\times 0.06\) -mm radial channel 100%. [ABSTRACT FROM PUBLISHER]

One of the experimental challenges in the study of nanomaterials in liquids in the (scanning) transmission electron microscope ((S)TEM) is gaining quantitative information. A successful experiment in the fluid stage will depend upon the ability to plan for sensitive factors such as the electron dose applied, imaging mode, acceleration voltage, beam-induced solution chemistry changes, and the specifics of solution reactivity. In this paper, we make use of a visual approach to show the extent of damage of different instrumental and experimental factors in liquid samples imaged in the (S)TEM. Previous results as well as new insights are presented to create an overview of beam–sample interactions identified for changing imaging and experimental conditions. This work establishes procedures to understand the effect of the electron beam on a solution, provides information to allow for a deliberate choice of the optimal experimental conditions to enable quantification, and identifies the experimental factors that require further analysis for achieving fully quantitative results in the liquid (S)TEM. [ABSTRACT FROM AUTHOR]

After three years of upgrading work, PLS-II (S. Shin, Commissioning of the PLS-II, JINST, January 2013) is now successfully operating. The top-up operation of the 3 GeV linear accelerator had to be delayed because of some challenges encountered, and PLS-II was run in decay mode at the beginning in March 2012. The main difficulties encountered in the top-up operation of PLS-II are different levels between the linear accelerator and the storage ring, the 14 narrow gap in-vacuum undulators in operation, and the full energy injection by 3 GeV linear accelerator. Large vertical emittance and energy jitter of the linac were the major obstacles that called for careful control of injected beam to reduce beam loss in the storage ring during injection. The following measures were taken to resolve these problems: (1) The high resolution Libera BPM (see http://www.i-tech.si) was implemented to measure the beam trajectory and energy. (2) Three slit systems were installed to filter the beam edge. (3) De-Qing circuit was applied to the modulator system to improve the energy stability of injected beam. As a result, the radiation by beam loss during injection is reduced drastically, and the top-up mode has been successfully operating since 19th March 2013. In this paper, we describe the experimental results of the PLS-II top-up operation and the improvement plan. [ABSTRACT FROM AUTHOR]

Solar coronal shocks are very common phenomena in the solar atmosphere and are believed to be the drivers of solar type II radio bursts. However, the microphysical nature of these emissions is still an open question. This paper proposes that electron cyclotron maser (ECM) emission is responsible for the generation of radiation from the coronal shocks. In the present model, an energetic ion beam accelerated by the shock first excites the Alfvén wave (AW), then the excited AW leads to the formation of a density-depleted duct along the foreshock boundary of the shock. In this density-depleted duct, the energetic electron beam produced via the shock acceleration can effectively excite radio emission by ECM instability. Our results show that this model may potentially be applied to solar type II radio bursts. [ABSTRACT FROM AUTHOR]

We report experimental results on a two frequency gyrotron, operating in the TE22,6 mode at 110 GHz and the TE24,7 mode at 124.5 GHz. The gyrotron uses the same electron gun as a previous single frequency 110-GHz gyrotron, with a new cavity and internal mode converter designed for optimized performance at the two frequencies. For a 98 kV, 42-A electron beam operating in 3- \mus pulses, an output power of 1.25 MW was obtained at 110 GHz (30% efficiency) and 1.0 MW at 124.5 GHz (24% efficiency). The highest power obtained was 1.4 MW with a 96 kV, 45-A beam (32% efficiency) at 110 GHz. In both modes, mode competition was minimal around the high-power operating point and operation was extremely stable. The output power and efficiency in the TE24,7 mode were limited by the electron beam quality. At both frequencies, excellent Gaussian beam content was found: 1) 99% for the TE22,6 mode and 2) 97% for the TE24,7 mode. Both output beams had waist radii of 2.65 cm, in very good agreement with theory. [ABSTRACT FROM PUBLISHER]

The experimental results of a promising pulsed plasma source, producing electron beams with a current density of up to 10 kA/cm^2 are presented. The beam duration was up to \sim1~\mus , in an accelerating voltage of up to \sim350~kV , without shorting of the cathode–anode gap by the cathode plasma. This plasma electron source is proven to sustain hundreds of pulses without degradation in its emission properties. The cathode plasma electron density ne\,\leq\,10^{15}~cm^{-3} , electron Te\leq 13~eV and ion Ti\leq 4~eV temperatures, and expansion velocity Vpl\leq 1.6\times 10^6~\rm cm/\rm s were determined using time- and space-resolved spectroscopy and light emission. [ABSTRACT FROM PUBLISHER]

The ITER first wall (FW) includes beryllium armor tiles joined to a CuCrZr heat sink. The FWs are one of the critical components in an ITER machine with a surface heat flux of 4.7 MW/ m^2 or above. The small-scale mockup shall be a part of the qualification tests and used to validate the performance of the dominant manufacturing technologies before the production of larger scale components, and this mockup shall be equipped with a hypervapotron heat sink and manufacturing processes developed for a semiprototype design. The small-scale mockup includes 48 beryllium armor tiles (12 mm $\times\,$ 12 mm) capable of withstanding the specified heat flux values. The tile thickness shall be 6 mm to minimize the beryllium surface temperature and evaporation under high thermal loads. The detailed fabrication process of semiprototype small-scale mockups was developed for a qualification test in Korea. For the CuCrZr and stainless steel, the canned materials are processed into an hot isostatic pressing (HIP) device. In the case of beryllium-to-CuCrZr joining, the HIP was conducted at 580 ^{\circ}{\rm C} and 100 MPa. For nondestructive tests of the fabricated semiprototypes, visual and dimension inspections were performed whenever needed during the fabrication process, and ultrasonic tests were performed using ultrasonic probes. Destructive tests for the qualification semiprototype were performed on a small-scale mockup, which was fabricated together with semiprototypes. The Korea heat load test facility using an electron beam system was constructed with an electron gun (maximum electric power of 800 kW) for a high heat flux application with a 300-kW high-voltage power supply and maximum accelerating voltage of 60 kV. This facility was operated to evaluate the performance test of plasma facing components. A cyclic heat flux test will be performed to evaluate the ITER qualification program. [ABSTRACT FROM PUBLISHER]

Central conductor is one of the key components of ion cyclotron ranges of heating antenna, which is usually formed by welding due to the complex structures. High level of welding seam quality and small deformation are very important to central conductor. Electron beam welding (EBW) is suggested as the central conductor welding. To meet EBW requirements and reduce the risk, complex and high level of the accuracy welding fixture have been designed for central conductor EBW. Some samples were manufactured to do test and examination for EBW qualification before central conductor welding. Based on the welding parameters, thermal analysis using finite element method for the welding seam have been carried out. One mockup of central conductor for EBW has been made for proving welding parameters. In addition, some postwelding process were employed after one central conductor EBW. Results of examination and inspection of one central conductor using EBW are presented in this paper. [ABSTRACT FROM PUBLISHER]

In present paper, the effect of relativistic hot electron beam for field aligned Whistler mode waves has been studied theoretically in the presence of AC electric field perpendicular to magnetic field. Studies have been performed using perturbative approach along with the method of characteristic solutions and are valid for comparatively small ambient magnetic field of Uranus, of the order of nano Tesla, as observed by Voyager 2. The detailed derivation and calculations has been done for dispersion relation and growth rate for magnetosphere of Uranus. Analyses are done by changing various plasma parameters which are explained in result and discussions section of this paper. Extensive study of wave-particle interactions and numerical calculations concludes that in case of injection of a distribution of particles having a positive slope in v⊥, temperature anisotropy remains the main source of free energy. It is seen that other effective parameters for the growth of whistler mode waves are AC frequency and higher number density of hot electrons. We also learn that even the minimal presence of such energetic particles having a positive slope of distribution function and increasing power of perpendicular thermal velocity can increase the growth rate significantly in the magnetosphere of Uranus. The present work is basically based upon the theoretical investigation and mathematical analysis of the magnetosphere of Uranus, supported by satellite data. [ABSTRACT FROM AUTHOR]

Spin polarized electron beam is often used in material characterizations which relates to magnetism as well as in the high energy particle physics. The manipulation of the spin polarization toward the arbitrary direction is indispensable in such studies. In the present work, a novel multipoleWien filter is proposed as the three-dimensional spin manipulator, and a prototype 8-pole Wien filter is developed. It is applied to spin polarized low energy electron microscopy, and the variation of the magnetic contrast with managing the spin polarization is evaluated. It is confirmed that the novel multipole Wien filter can manipulate the spin polarization three-dimensionally. [ABSTRACT FROM AUTHOR]

A possible route toward achieving high-power microwave (HPM) devices is through the use of novel slow-wave structures, represented by multiple coupled transmission lines (MTLs), and whose behavior when coupled to electron beams has not been sufficiently explored. We present the extension of the 1-D linearized Pierce theory to MTLs coupled to a single electron beam. We develop multiple formalisms to calculate the $k-\omega$ dispersion relation of the system and find that the existence of a growing wave solution is always guaranteed if the electron propagation constant is larger than or equal to the largest propagation constant of the MTL system. We verify our findings with illustrative examples that bring to light unique properties of the system in which growing waves were found to exist within finite bands of the electron propagation constant and also present possible means to improve the gain. By treating the beam-MTL interaction as distributed dependent current generators in the MTL, we derive relations characterizing the power flux and energy exchange between the beam and the MTLs. For the growing wave, we show that the beam always behaves as an energy source causing power flux along the transmission lines. The theory developed in this paper is the basis for the possible use of degenerate band edges in periodic MTL systems for HPM amplifiers. [ABSTRACT FROM PUBLISHER]

The wakefield acceleration in a dual grating waveguide slow wave structure (DGWSWS) is proposed. Analytical expression of the wakefield amplitude and frequency is calculated. The wakefield amplitude is analyzed in terms of the grating waveguide parameters, i.e., grating width and grating slot height. The results indicate that the grating wakefield accelerators with shallower slots can operate at terahertz with competitive accelerating gradients when compared with a dielectric wakefield accelerator. [ABSTRACT FROM PUBLISHER]

In this paper, we present the design of a microwave generator using metamaterials (MTMs) in a negative index waveguide interacting with a high-power electron beam. The microwave structure is formed by inserting two MTM plates loaded with complementary split-ring-resonators (CSRRs) into a rectangular waveguide. Electromagnetic simulations using the high-frequency structure simulator code confirm the presence of a negative index TM-like mode suitable for use in a backward-wave oscillator (BWO). Particle-in-cell (PIC) simulations using the computer simulation technology (CST) Particle Studio code are performed to evaluate the efficiency of an S-Band MTM-based BWO (MTMBWO) excited by a 500 keV, 80-A electron beam. After about 250 ns, the MTMBWO reaches a saturated output power of 5.75 MW with an efficiency of 14% at a frequency near 2.6 GHz. The MTMBWO is also modeled by representing the MTM plates, which consist of CSRRs, as dielectric slabs whose effective permittivity is given by a Lorentzian model. The dielectric slab model is also simulated with the CST PIC code and shows good qualitative agreement with the simulations including the CSRR loaded plates. A cold test structure was fabricated from brass to test the theoretical predictions of the microwave transmission versus frequency of the negative index waveguide. Test results using a vector network analyzer showed very good agreement with the simulations for the excitation of the negative index TM-like mode near 2.6 GHz. The proposed structure appears to be promising for use in a MTMBWO high-power microwave generator. [ABSTRACT FROM PUBLISHER]

Quite unexpectedly with respect to the numerical and analytical results found in literature, we establish a new range for the real parameter b for which the existence of 2π-periodic solutions of the Brillouin focusing beam equation ẍ + b(1 + cos t)x = 1/x is guaranteed. This is possible thanks to suitable nonresonance conditions acting on the rotation number of the solutions in the phase plane. [ABSTRACT FROM AUTHOR]

When an un-gated thermionic cathode is operated in a radio-frequency gun, some fraction of the emitted electrons will return to the cathode due to the change in sign of the electric field in the gun. This back-bombardment current causes heating of the cathode, and this reduces the ability of the cathode heater to control the bunch charge. In this paper, we investigate the fundamental factors in single-frequency back-bombardment for a short-gap electron gun. Simulations revealed that the back-bombardment power depends strongly on the operating frequency and the bunch charge. Additionally, the use of a two-frequency TM010/TM{020} electron gun to mitigate this effect was investigated which revealed that the effectiveness of this technique depends strongly upon single-frequency back-bombardment power but with the optimal reduction in back-bombardment power (62% of the baseline) occurring in the low-frequency limit. [ABSTRACT FROM PUBLISHER]

By imaging the spatial intensity distribution of the electrons from a Stoffel-Johnson (SJ) type low energy electron source for inverse photoemission spectroscopy (IPES), we find that the focus is distorted when the beam current exceeds the limiting value due to space charge effect. The space charge effect and the contact potential difference suppress the beam current at low energies (<10 eV). In this work, we show that these limitations of the SJ source can be overcome by compensation of the contact potential difference between the cathode and the lens electrodes and an uniform well focused electron beam with the set kinetic energy can be obtained. The size of the electron beam is around 1 mm full width at half maximum over the whole energy range of 5 to 30 eV generally used for IPES. The compensation of the contact potential difference also enhances the beam current substantially at low energies (<10 eV) and uniform beam current is achieved for the whole energy range. We find that the drift in the electron beam position is sensitive to the lens electrode separation and it is about 1 mm over the whole energy range. By measuring the n = 1 image potential state on Cu(100), we show that the resolution is better when the cathode filament current is set to lower values. [ABSTRACT FROM AUTHOR]

The article presents a study to examine whether the electrons carry momentum by referring to an experiment by scientist William Crookes using paddle wheel placed inside a cathode ray tube (CRT). Topics discussed include contribution of physicist J. J. Thomson to observe the motion of the wheel due to radiometric effect, effect of impulsive force supplied to the electron beam in the CRT, and analysis of the moment of inertia of the wheel along with its mass and dimensions.

It is shown in the case of capacitive discharge excilamps that the thermal power of the discharge is proportional to the volume filling coefficient of the discharge. It is proposed to treat the found phenomenon as an analog of the effect of the normal current density of a barrier discharge. [ABSTRACT FROM AUTHOR]

The physics program at the upgraded Jefferson Lab (JLab) and the physics program envisioned for the proposed electron-ion collider (EIC) include large efforts to search for interactions beyond the Standard Model (SM) using parity violation in electroweak interactions. These experiments require precision electron polarimetry with an uncertainty of < 0.5\%. The spin dependent Synchrotron radiation (SR), called “spin-light,” can be used to monitor the electron beam polarization. In this article we develop a conceptual design for a “spin-light” polarimeter that can be used at a high intensity, multi-GeV electron accelerator. We have also built a Geant4 based simulation for a prototype device and report some of the results from these simulations. [ABSTRACT FROM PUBLISHER]