Thick Electron Beam Research Articles

Numerical Simulation of 50 mm 316L Steel Joint of EBW and Its Experimental Validation

The 316L thick plate electron beam welding (EBW) has been widely used in fusion test reactor manufacturing. Therefore, the numerical simulation of the 50 mm 316L austenitic stainless steel by two heat sources and experimental on microstructure and residual stress have been studied in this article. In the simulation study, the traditional heat source model (3D Gaussian heat source) and composite heat source (double ellipsoid heat source superimposed on the 3D Gaussian heat source) were proposed to simulate the welding of local joint. Weld cross-section, temperature curve, and residual stress after welding obtained by simulations were investigated. The experimental study involved residual stress tests and microstructure analysis. It turned out that the result of the composite heat source was closer to the actual joint. The residual stress distribution of simulation was validated and in accordance with experimental measurement. Moreover, the microstructures were studied by electro backscattered diffraction (EBSD) and compared with the temperature curve. The formation mechanism of microstructural heterogeneity was caused mainly by different thermal cycles at different positions of the thick plate. The top of the joint was more prone to stress concentration.

Unveiling Liquation and Segregation Induced Failure Mechanism in Thick Dissimilar Aluminum Alloy Electron-Beam Welds

This study presents new findings on the underlying failure mechanism of thick dissimilar electron-beam (EB) welds through a study on the AA 2219-AA 5083 pair. Contrary to the prior studies on EB welding of thin Al alloys, where liquation in the grain boundaries (GBs) in the partially melted zone (PMZ) was not observed, the present investigation for thick EB welds reports both liquation and increased segregation of Cu in the PMZ. The work is thus directed towards understanding the unusual observation in the PMZ of thick EB weld through investigation of the microstructural variation across the various regions of the produced weld. The microstructural results are correlated with the mechanical properties of the weld, i.e., hardness variation and tensile response. Results of this investigation suggest that unlike the convention that EB welding produces sound dissimilar Al welds, the weld performance for thick EB Al welds is affected by the heat input, the associated cooling rates, and most importantly by the base material thickness. Extensive liquation and Cu segregation induced failure in the PMZ on the AA 2219 side of the dissimilar weld. The underlying failure mechanism is explained through a heat-transfer analysis. Beyond a certain plate thickness, the heat transfer changes from two to three-dimensional. As a result, retarded cooling promotes liquation and Cu segregation in thick EB welds.

Heterogeneous microstructure and associated mechanical properties of thick electron beam welded Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy joint

The non-uniform temperature field and cooling rates in the molten pool during solidification process fabricate microstructural and mechanical heterogeneities in fusion zone (FZ) and heat-affected zone (HAZ) of thick titanium alloy weldment. In this study, electron beam welding was used to assemble thick Ti-5Al-2Sn-2Zr-4Mo-4Cr (TC17) alloy plates. Microstructural heterogeneity concerning recrystallized martensitic structures with different morphology and distribution features in FZ and retained microstructures after experiencing thermal exposure in HAZ were analyzed to unravel their effects on multiscale mechanical behavior. It was found that needle-shaped martensite (α') exhibited a comparative high nano hardness and the precipitation of needle-shaped martensite cluster contributed to a more severe tensile strain localization in FZ and premature brittle fracture of the joint. The bottom layer of weldment, where the FZ was verified to be martensitic free, exhibited a better combination of strength and ductility. Mo and Al exhibited a better thermostability than Cr, which held the responsibility for the microstructural stability in HAZ during severe thermal exposure after welding.

Towards Solventless Processing of Thick Electron-Beam (EB) Cured Lithium-Ion Battery Electrodes

The development of high energy density and low cost Li-ion batteries is important for portable electronics and electric vehicle applications. It has been reported that electrode processing, especially for the cathode, with conventional manufacturing methods accounts for considerably high cost in Li-ion batteries [1,2]. Electrodes used in conventional lithium-ion batteries are manufactured through a slurry coating process, where a significant amount of solvent is required, and it takes at least several minutes for the solvent to evaporate. Given the high coating speeds necessary (up to 100 feet per minute) the drying zone may be several hundred feet long, which occupies a large footprint in battery manufacturing plants. Here we propose manufacturing Li-ion battery cathodes using electron beam (EB) curing, which eliminates the using of solvents and allows the electrode to be cured at high speed. Solventless processing of powder coating and high speed curing at 500 feet per minute will also be discussed. Such a novel processing approach presents an exciting new avenue for manufacturing research of high performance, low cost Li-ion batteries. Acknowledgements This research at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) under contract DE-AC05-00OR22725, was sponsored by the Office of Energy Efficiency and Renewable Energy (EERE) Vehicle Technologies Office(VTO) (Deputy Director: David Howell) Applied Battery Research subprogram (Program Manager: Peter Faguy).

On the clinotron effect in a backward-wave tube

The results of a theoretical study of the clinotron effect in a clinotron model, which takes into account static electron trajectories in the focusing magnetic field and the initial spacing between the lower beam boundary and the surface of the slow-wave structure, are presented. Physical processes of interaction between a thick electron beam with transverse dimensions comparable with the length of the slow wave and the RF field at its oblique incidence onto the structure are considered. It is demonstrated that, as the current is increased from the starting to the working value, a beam tilt is necessary to reduce the nonlinear effects of interaction between the beam and the RF field and prevent the complex self-oscillation dynamics in the clinotron; in the small amplitude mode (start), the beam tilt is related to optimization of the beam supply into the interaction space, which ensures the minimum starting current. In addition, it is shown that, in the presence of the initial spacing between the beam and structure, the reduced clinotron efficiency η/С increases and, at the optimum tilt angle, is no less than the normalized efficiency of classical backward-wave tubes with a thin electron beam.

Measured and predicted residual stresses in thick section electron beam welded steels

Four steel thick-section components, created by electron beam (EB) welding, were measured to obtain their residual stress distributions. Two components were made from ferritic steel and two components manufactured from stainless steel. All four components were measured in the as-welded state, with one ferritic steel component then subjected to post-weld heat treatment (PWHT) and measured. Distributions of the principal residual stresses were measured, across the EB welds and through the weld centrelines. Finite element models simulated the welding processes and the predicted residual stresses were compared to the measurements. In the ferritic steel components it was found that the peak residual stresses occur either side of the weld outside of the heat affected zone, with magnitudes corresponding to parent material yield strengths. After PWHT the measured peak stresses reduced from about 600 MPa to 90 MPa. Compressive residual stresses were found at the EB weld entrance and exit positions of the ferritic steel. This was not observed in the stainless steel EB welds, where tensile stresses were measured in the as-welded state. Overall the profiles of the residual stresses predicted by FE analyses replicated the measurements, but the FE analyses always predicted higher peak values. It was found that the measured distribution of residual stresses across the ferritic steel components are very similar irrespective of component thickness and weld speed, with the tensile stresses confined to distances of about 40% of the component thickness. In contrast in a stainless steel component the tensile stresses are much more broadly distributed about the weld centreline.

Self-modulation of the output signal in clinotron

It is demonstrated that the self-modulation of the output signal in clinotron results from a delayed response of the distributed system of clinotron to the action of nonlinearity in the interaction of layers of a thick electron beam and high-frequency field. The effect differs from the self-modulation in a conventional O-type BWT, which is determined by the beam as a whole.

The oscillation adjustment in clinotron

Linear and nonlinear stages of the oscillation adjustment in a model of a source of millimeter-wavelength radiation (clinotron) are analyzed using the nonstationary theory of interaction in a system consisting of a thick electron beam and a backward wave. The duration of the transient process is studied as a function of the ratio of the working and starting currents and an angle of incidence on the surface of a slow-wave structure. It is demonstrated that the minimum duration of the process is reached in the vicinity of the optimal regime in which the beam is completely deposited on the surface of the slow-wave structure.

Improved models for synchrotron radiation sources in SHADOW

A technique to improve the description of synchrotron sources is proposed and applied to the ray tracing code SHADOW. Using a dedicated synchrotron radiation calculation code, it is possible to calculate the single electron emission, as well as the thick electron beam emission. Two methods will be introduced. The first simulates synchrotron radiation using the spatial electron distribution for the positions of the rays and the thick electron beam spectral-angular distribution in the far field for their directions and their energies. The second method derives the variation of the single electron spectral-angular distribution with respect to the electron direction and the electron energy, and simulates the rays emitted by each electron. A preprocessor for SHADOW has been developed to read the intensity distribution from an HDF5 file generated by SRW. The final rays have been used to simulate future beamlines and have been cross checked with the wavefront propagation method.

Improved Efficiency of Backward-Wave Oscillator With an Inclined Electron Beam

The possibility of the efficient operation of a backward-wave oscillator (BWO) with an electron beam inclined with respect to the surface of a periodic structure-a clinotron-is analyzed here. The beam inclination provides the possibility of effective interaction by all particles of a thick electron beam with the slow evanescent harmonic of the cavity modes. The problem of electron-beam-wave interaction is treated in a self-consistent formulation. A theoretical analysis shows that the inclination of the electron beam to the grating surface decreases the demand of the clinotron for magnetic field magnitude and beam velocity spread compared to a conventional BWO. It is demonstrated that, for an optimal inclination angle and an optimal beam thickness, the clinotron efficiency exceeds the efficiency of a conventional BWO considerably given the same electron beam parameters. The developed multimode theory results are in satisfactory agreement with the theory of a BWO in terms of reflections and particle-in-cell simulations.

Controlling the Cut in Contour Residual Stress Measurements of Electron Beam Welded Ti-6Al-4V Alloy Plates

The multiple cut contour method is applied to map longitudinal and transverse components of residual stress in two nominally identical 50 mm thick electron beam welded Ti-6Al-4V alloy plates, one in the as-welded condition and a second welded plate in a post weld heat treated (PWHT) condition. The accuracy and resolution of the contour method results are directly linked to the quality of the electro-discharge machining cut made. Two symmetric surface contour artefacts associated with cutting titanium, surface bowing and a flared edge, are identified and their influence on residual stresses calculated by the contour method is quantified. The former artefact is controlled by undertaking a series of cutting trials with reduced power settings to find optimal cutting conditions. The latter is mitigated by attaching 5 mm thick sacrificial plates to the wire exit side of the test specimen. The low level of noise in the measured stress profiles for both the as-welded and PWHT plates demonstrates the importance of controlling the quality of a contour cut and the added value of undertaking cutting trials.

Study of high frequency characteristics of metallic-pole-planar slow wave structure

The discrete metallic-pole-planar slow wave structure (SWS) is introduced in this paper, and the high frequency characteristics are studied. And procedures based on three-dimensional finite-difference time-domain (3-D FDTD) arithmetic are used to calculate the dispersive characteristics of the new SWS, and HFSS simulation software is used to analyze the coupling impedance. Results show the high frequency characteristics of the pole structure not only have a general similarity in comparison with these of the grating, but also have itself advantages. For the electrons moving between multiple poles of the structure, the interaction impedances are symmetry; relatively thick electron beams can efficiently interact with the high-frequency field while it used as the high frequency system of vacuum electronic devices. This kind of SWS is promising to lower the starting current density and have better efficiency than the traditional grating SWS. According to the results, a sub-millimeter radiation source driven by the multiple beams can be designed at a low operating current density.

Numerical Analysis of Slow-Wave Instabilities in an Oversized Sinusoidally Corrugated Waveguide Driven by a Finitely Thick Annular Electron Beam

Three kinds of models are used for beam instability analyses: those based on a solid beam, an infinitesimally thin annular beam, and a finitely thick annular beam. In high-power experiments, the electron beam is an annulus of finite thickness. In this paper, a numerical code for a sinusoidally corrugated waveguide with a finitely thick annular beam is presented and compared with other models. Our analysis is based on a new version of the self-consistent linear theory that takes into account three-dimensional beam perturbations. Slow-wave instabilities in a K-band oversized sinusoidally corrugated waveguide are analyzed. The dependence of the Cherenkov and slow cyclotron instabilities on the annular thickness and guiding magnetic field are examined.

ENERGY RELEASE AND TRANSFER IN SOLAR FLARES: SIMULATIONS OF THREE-DIMENSIONAL RECONNECTION

Using three-dimensional magnetohydrodynamic simulations we investigate energy release and transfer in a three-dimensional extension of the standard two-ribbon flare picture. In this scenario, reconnection is initiated in a thin current sheet (suggested to form below a departing coronal mass ejection) above a bipolar magnetic field. Two cases are contrasted: an initially force-free current sheet (low beta) and a finite-pressure current sheet (high beta), where beta represents the ratio between gas (plasma) and magnetic pressure. The energy conversion process from reconnection consists of incoming Poynting flux turned into up- and downgoing Poynting flux, enthalpy flux, and bulk kinetic energy flux. In the low-beta case, the outgoing Poynting flux is the dominant contribution, whereas the outgoing enthalpy flux dominates in the high-beta case. The bulk kinetic energy flux is only a minor contribution in the downward direction. The dominance of the downgoing Poynting flux in the low-beta case is consistent with an alternative to the thick target electron beam model for solar flare energy transport, suggested recently by Fletcher & Hudson, whereas the enthalpy flux may act as an alternative transport mechanism. For plausible characteristic parameters of the reconnecting field configuration, we obtain energy release timescales and energy output rates that compare favorably with those inferred from observations for the impulsive phase of flares. Significant enthalpy flux and heating are found even in the initially force-free case with very small background beta, resulting mostly from adiabatic compression rather than Ohmic dissipation. The energy conversion mechanism is most easily understood as a two-step process (although the two steps may occur essentially simultaneously): the first step is the acceleration of the plasma by Lorentz forces in layers akin to the slow shocks in the Petschek reconnection model, involving the conversion of magnetic energy to bulk kinetic energy. However, due to pressure gradient forces that oppose the Lorentz forces in approximate, or partial force balance, the accelerated plasma becomes slowed down and compressed, whereby the bulk kinetic energy is converted to heat, either locally deposited or transported away by enthalpy flux and deposited later. This mechanism is most relevant in the downflow region, which is more strongly governed by force balance; it is less important in the outflow above the reconnection site, where more energy remains in the form of fast bulk flow.

A Theory of the Orotron with an Inclined Electron Beam

A linear and non-linear theory of the orotron with an electron beam inclined with respect to the surface of a periodic structure is presented. The beam inclination provides the possibility of the effective interaction of all particles of thick electron beam with slow evanescent harmonic of the cavity mode. On the basis of obtained analytical expression for the orotron starting current, the possibility to increase the device frequency up to 600 GHz is discussed. According to numerical simulations, the inclination of the beam allows increasing significantly both the electron efficiency and the output power of the device. The project of low-voltage orotron with the operating frequency of 100 GHz and output power of 10 W is proposed.

Superconducting NbN nanowire photo switches for generating single flux quantum pulses

We investigated superconducting NbN nanowire as a photo switch for generating single flux quantum (SFQ) pulses. Epitaxially grown NbN thin films were prepared on MgO(100) substrates by a dc magnetron sputtering method using gas mixture of Ar+N2, without substrate heating. NbN thin films showed Tc of 13.6 K for 8 nm, and 10 K for 4 nm. NbN nanowires were patterned using a electron beam lithography with 200 nm thick electron beam resist. To increasing photo-sensitive regions, we fabricated 50 × 50 μm2 meander patterns with NbN nanowires. Line width of nanowires was varied from 150 nm to 500 nm. Critical current density of NbN nanowires was about 3×106A/cm2 at 4.2 K. We irradiated 850-nm laser pulses via 50-μm multi-mode optical fibers. Repetition frequency and pulse width could be controlled by a pulse pattern generator. The maximum laser pulse power was about 1 mW. Using 150-nm-wide NbN nanowires, half of critical current was suppressed by 1 mW CW laser irradiations. High speed responses were observed for laser pulses with repetition frequency of 1 MHz and pulse width of 2 ns. Besides the NbN nanowire photo switches, we designed an SFQ interface circuit based on Josephson transmission lines. The designed circuit could generate SFQ pulses by input current of 10 μA, 25 GHz current pulses. Dc bias margin of the circuit was ±15% for 60 μA current pulses.

Theoretical analysis of a relativistic travelling wave tube filled with plasma

A cold and uniform plasma-filled travelling wave tube with sinusoidally corrugated slow wave structure is driven by a finite thick annular intense relativistic electron beam with the entire system immersed in a strong longitudinal magnetic field. By means of the linear field theory, the dispersion relation for the relativistic travelling wave tube (RTWT) is derived. By numerical computation, the dispersion characteristics of the RTWT are analysed in different cases of various geometric parameters of the slow wave structure and plasma densities. Also the gain versus frequency for three different plasma densities and the peak gain of the tube versus plasma density are analysed. Some useful results are obtained on the basis of the discussion.

Cryogenic etch process development for profile control of high aspect-ratio submicron silicon trenches

A cryogenic etch process using low temperature (T⩽−100°C) and SF6 and O2 gases is presented for fabricating high aspect ratio silicon microstructures, including photonic devices and micro- and nanoelectromechanical systems. The process requires only a single electron beam resist mask and results in open area etch rates of 4μm∕min. Various etch process parameters, including O2 flow, rf forward power, substrate temperature, and chamber pressure were studied, and the resulting effect on the etch quality was evaluated in terms of sidewall verticality and surface roughness. The optimized process uses low temperature (T=−110°C) and low chamber pressure (P=7mTorr) and enables sidewall verticality greater than 89.5° with roughness of 1–10nm. A silicon etch selectivity of 26:1 was obtained for 380nm thick electron beam resist. Using the optimized process, a silicon-on-insulator Fabry-Pérot optical cavity with integrated rib waveguides and deeply etched silicon/air distributed Bragg reflector mirrors was fabricated and tested. The device exhibits sharp resonance peaks with full width at half maximum Δλ=0.45nm, free-spectral range of 26 nm, finesse F=58, and quality factor Q=3400 (at λ0=1531.6nm). The optical measurements and extracted mirror reflectance (R≈95%) confirm the high quality of our optimized etch process.

Magnetic nanowires patterned in the La 2/3Sr 1/3MnO 3 half-metal

Bridge-shaped magnetic nanowires have been designed and patterned in half-metallic La 2/3Sr 1/3MnO 3 thin films, using a thick negative-tone electron beam lithography (EBL) process. EBL was performed in the high resolution hydrogen silsesquioxane (HSQ) inorganic resist. This paper reports on the optimization of EBL, for which both electron beam proximity effects and pre-bake annealing temperatures have been studied. To take benefit of the proximity effects, a special bridge geometry is proposed. Hundred nanometre-wide nanowires with large aspect ratio (⩾2) have been successfully patterned and transferred in LSMO.

Sub-micron metallic electrothermal actuators

The scaling down of electromechanical devices from micrometer scales to nano scales is of great interest. This paper presents fabrication and characterization of sub-micron high aspect ratio metallic electrothermal actuators using a combination of electron beam lithography and electroplating techniques. A 1.2 µm thick SU-8 layer was used as a sacrificial layer and a 1 µm thick electron beam lithography-processed polymethyl methacrylate resist was used to form 3:1 aspect ratio sub-micron (minimum feature size of 350 nm) electroplated nickel electrothermal actuators. Such sub-micron electrothermal actuators were characterized by a nanomanipulator system in a scanning electron microscopy system. Electro-thermo-mechanical finite element analysis (FEA) of the actuator using ANSYS was carried out and the FEA results were in good agreement with the measured results. Displacements at the tip of the actuator of 370 nm were reproducibly observed with the applied voltages of 145 mV. This work can be applied to realize more sophisticated nano actuators which can manipulate sub-micron scale objects.