Hot Electron Beam Research Articles

Nanoscale subsurface imaging by non-steady-state electron beam-driven scanning thermoelectric capacitance microscopy

Nanoscale subsurface characterization technologies based on the scanning electron microscope platform offer incomparable advantages of nondestructiveness and penetration depths up to the micrometer scale. However, the electron beam can serve not just as a mechanical/electrical excitation source but also as an excellent nanoscale thermal excitation source, which can facilitate the development of nanoscale subsurface imaging methods based on the Seebeck effect in semiconducting materials. In this work, a subsurface nondestructive imaging technology, scanning thermoelectric capacitance microscopy (STeCM), was developed based on the interaction between a non-steady-state electron beam and semiconducting materials, exploiting the Seebeck effect. In STeCM, a square wave-modulated hot electron beam with huge kinetic energy excites a “thermal wave” in the subsurface local region of the semiconducting sample. The heated local region, acting as a thermoelectric capacitor, undergoes cyclic charging and discharging, leading to the generation of periodic current due to non-equilibrium carrier migration. The second-order harmonic component of this current is demodulated to visualize embedded local thermal/thermoelectric inhomogeneities. Amazingly, for STeCM sample, only a smooth or polished surface is required, eliminating the need for any microfabrication, which will effectively decrease the configuration difficulty in the experiment. STeCM offers an alternative subsurface nondestructive imaging technology for more efficient, simple, and robust characterization.

A Mechanism for Large-Amplitude Parallel Electrostatic Waves Observed at the Magnetopause

Large-amplitude electrostatic waves propagating parallel to the background magnetic field have been observed at the Earth’s magnetopause by the Magnetospheric Multiscale (MMS) spacecraft. These waves are observed in the region where there is an intermixing of magnetosheath and magnetospheric plasmas. The plasma in the intermixing region is modeled as a five-component plasma consisting of three types of electrons, namely, two counterstreaming hot electron beams and cold electrons, and two types of ions, namely, cold background protons and a hot proton beam. Sagdeev pseudo-potential technique is used to study the parallel propagating nonlinear electrostatic solitary structures. The model predicts four types of modes, namely, slow ion-acoustic mode, fast ion-acoustic mode, slow electron-acoustic mode and fast electron-acoustic modes. Except the fast ion-acoustic mode, all other modes support solitons. Whereas slow ion-acoustic solitons have positive potentials, both slow and fast electron-acoustic solitons have negative potentials. For the case of 4% cold electron density, the slow ion-acoustic solitons have electric field ∼(40–120) mV m−1. The fast Fourier transforms (FFT) of slow ion-acoustic solitons produce broadband frequency spectra having peaks between ∼100 Hz to 1000 Hz. These theoretical predictions are in good agreement with the observations. The slow and fast electron-acoustic solitons could be relevant in explaining the low-intensity high (>1 kHz) frequency waves which are also observed at the same time.

Enhanced target normal sheath acceleration with a grooved hydrocarbon target

The interaction of a high-intensity ultrashort laser pulse with a few micrometers-thick hydrocarbon target is known to accelerate protons/ions to multi-MeV, on the rear side of the target, via the mechanism of target normal sheath acceleration. Micro-structuring the target front is one of the promising approaches to enhance the cutoff energy as well as to reduce the divergence of accelerated protons/ions. In this paper, the interaction of a normally incident intense laser pulse with targets having single micrometer-sized grooves, at their front side, of semi-circular, triangular, and rectangular shapes has been studied by using two-dimensional particle-in-cell simulations. It is observed that as compared to a flat target for targets with a rectangular groove at the front side the focused hot electron beam at the rear side results in an approximately fourfold increase in the cutoff energy of accelerated protons. For triangular and semi-circular groove targets, the cutoff energy remains comparatively lower (higher than the flat target though). The angular divergence of the accelerated protons/ions is also found to be relatively much lower in the case of a rectangular groove.

Estimation of plasma parameters of X-pinch with time-resolved x-ray spectroscopy

We estimate the parameters of a Cu plasma generated by an X-pinch by comparing experimentally measured x-rays with synthetic data. A filtered absolute extreme ultraviolet diode array is used to measure time-resolved x-ray spectra with a spectral resolution of ∼1 keV in the energy range of 1–10 keV. The synthetic spectra of Cu plasmas with different electron temperatures, electron densities, and fast electron fractions are calculated using the FLYCHK code. For quantitative comparison with the measured spectrum, two x-ray power ratios with three different spectral ranges are calculated. We observe three x-ray bursts in X-pinch experiments with two Cu wires conducted on the SNU X-pinch at a current rise rate of ∼0.2 kA/ns. Analysis of the spectra reveals that the first burst comprises x-rays emitted by hot spots and electron beams, with characteristics similar to those observed in other X-pinches. The second and third bursts are both generated by long-lived electron beams formed after the neck structure has been completely depleted. In the second burst, the formation of the electron beam is accompanied by an increase in the electron density of the background plasma. Therefore, the long-lived electron beams generate the additional strong x-ray bursts while maintaining a plasma channel in the central region of the X-pinch. Moreover, they emit many hard x-rays (HXRs), enabling the SNU X-pinch to be used as an HXR source. This study confirms that the generation of long-lived electron beams is crucial to the dynamics of X-pinches and the generation of strong HXRs.

Simulations of hot electron transport in the radiation-ablated plasmas

Abstract The transport of hot electrons in inertial confinement fusion (ICF) is integrated problem due to the coupling of hydrodynamic evolution. Here a hot electron transport code is developed and coupled to the radiation hydrodynamic code MULTI1D. Using the code, the hot electron beam slowing-down and ablation processes are simulated. The ablation pressure scaling law of hot electron beams is confirmed in our simulations. We attempt to simulate the hot electron transport in the condition of indirect drive ICF, where the spatial profile of hot electron energy deposition is presented around the compressed region. It is shown the hot electron can prominently increase the total ablation pressure in the early phase of radiation-ablated plasmas. So, our studies suggest a potential driven asymmetry mechanism may occur due to irradiation of asymmetry energetic hot electron beam. The possible degradation from the hot electron transport and preheating is also discussed.

Expression of Concern: Effect of Heat Treatment on the Properties of Electron Beam Welded Joint of First Wall

The structural material of the water-cooled ceramic breeder (WCCB) blanket is reduced activated ferrite/martensite (RAFM) steels. The first wall (FW) of one of its components is realized by hot isostatic pressure (HIP) diffusion welding and vacuum electron beam welding (EBW). In order to study the performance difference of electron beam welded joint of RAFM steels before and after heat treatment, the EBW test of RAFM steels was carried out, and the welded joint was quenched and tempered treatment. The properties of welded joints before and after quenched and tempered treatment were studied. The results show that the microstructure of the weld is composed of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\delta $ </tex-math></inline-formula> ferrite and coarse lath martensite. After quenching and tempering treatment, the microstructure of the joint changes into tempered martensite with no obvious martensite characteristics. Moreover, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\delta $ </tex-math></inline-formula> ferrite disappears, and carbide precipitates out at the original austenite grain boundaries. Here, the type of precipitated carbide is M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">23</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> as characterized by the electron backscatter diffraction analysis.

The Role of the Mechanical, Structural, and Thermal Properties of Poly(l-lactide-co-glycolide-co-trimethylene carbonate) in the Development of Rods with Aripiprazole

In this work, we aimed to determine the role of the mechanical, structural, and thermal properties of poly(l-lactide-co-glycolide-co-trimethylene carbonate) (P(l-LA:GA:TMC)) with shape memory in the formulation of implantable and biodegradable rods with aripiprazole (ARP). Hot melt extrusion (HME) and electron beam (EB) irradiation were applied in the formulation process of blank rods and rods with ARP. Rod degradation was carried out in a PBS solution. HPLC; NMR; DSC; compression and tensile tests; molecular weight (Mn); water uptake (WU); and weight loss (WL) analyses; and SEM were used in this study. HME and EB irradiation did not influence the structure of ARP. The mechanical tests indicated that the rods may be safely implanted using a pre-filled syringe. During degradation, no unfavorable changes in terpolymer content were observed. A decrease in the glass transition temperature and the Mn, and an increase in the WU and the WL were revealed. The loading of ARP and EB irradiation induced earlier pore formation and more intense WU and WL changes. ARP was released in a tri-phasic model with the lag phase; therefore, the proposed formulation may be administered as a delayed-release system. EB irradiation was found to accelerate ARP release.

Generation of oblique electromagnetic wave by hot injection electron beam with parallel AC electric field in the magnetosphere of Saturn

The Cassini radio and plasma wave investigation is designed to study radio emissions, plasma waves, thermal plasma, and dust in the vicinity of Saturn. Plasma particles, waves and fields are the major factors on which present knowledge about Saturn’s magnetosphere is based from the three flyby missions. For the present work, our examination is focused to study those waves who have frequency lower than electron cyclotron frequency in Saturnian magnetosphere. In this paper, we investigate the growth rate of whistler mode waves in magneto-plasma of Saturn. A dispersion relation for parallel propagating whistler mode waves has been applied to the magnetosphere of Saturn. The effect of electron density, temperature anisotropy, number density and A.C frequency on the temporal growth rate of the whistler mode emission is studied. For the given magnetic field and external electric field configuration, the general dispersion relation has been derived.

Radiative Characteristics of Reversed Polarity Gas-Puff Ar and Kr Plasmas

Experiments with regular and reversed polarities were carried out on the SHOTGUN-III Z-pinch device at Nihon University, Japan. SHOTGUN’s storage section consists of the 12- $\mu \text{F}$ fast capacitor bank, which was charged to 25 kV for these experiments and provided current up to 200 kA. The Ar and Kr gases were puffed between the electrodes through a hollow nozzle using a fast gas valve. Time-resolved X-ray detectors, time-integrated X-ray pinhole camera and two spectrometers, and an optical framing camera were applied for the study of radiative properties of Ar and Kr gas puffs. K-shell Ar spectra (3.9–4.2 A) and L-shell Kr spectra (6.3–7.6 A) show much intense He- and Li-like Ar and Ne- and Na-like Kr spectral features, respectively, and the evidence of the electron beams in reversed polarity experiments. The influence of reversed polarity on gas-puff plasma radiative characteristics and X-ray spectroscopic measurements is discussed. The advantages of using K-shell Ar and L-shell Kr for hot electron beam diagnostics are highlighted.

Nonlinear Electrostatic Steepening of Whistler Waves: The Guiding Factors and Dynamics in Inhomogeneous Systems

AbstractWhistler mode chorus waves are particularly important in outer radiation belt dynamics due to their key role in controlling the acceleration and scattering of electrons over a very wide energy range. The efficiency of wave‐particle resonant interactions is defined by whistler wave properties which have been described by the approximation of plane linear waves propagating through the cold plasma of the inner magnetosphere. However, recent observations of extremely high‐amplitude whistlers suggest the importance of nonlinear wave‐particle interactions for the dynamics of the outer radiation belt. Oblique chorus waves observed in the inner magnetosphere often exhibit drastically nonsinusoidal (with significant power in the higher harmonics) waveforms of the parallel electric field, presumably due to the feedback from hot resonant electrons. We have considered the nature and properties of such nonlinear whistler waves observed by the Van Allen Probes and Time History of Events and Macroscale Interactions define during Substorms in the inner magnetosphere, and we show that the significant enhancement of the wave electrostatic component can result from whistler wave coupling with the beam‐driven electrostatic mode through the resonant interaction with hot electron beams. Being modulated by a whistler wave, the electron beam generates a driven electrostatic mode significantly enhancing the parallel electric field of the initial whistler wave. We confirm this mechanism using a self‐consistent particle‐in‐cell simulation. The nonlinear electrostatic component manifests properties of the beam‐driven electron acoustic mode and can be responsible for effective electron acceleration in the inhomogeneous magnetic field.

Existence domain of electrostatic solitary waves in the lunar wake

Electrostatic solitary waves (ESWs) and double layers are explored in a four-component plasma consisting of hot protons, hot heavier ions (He++), electron beam, and suprathermal electrons having κ-distribution using the Sagdeev pseudopotential method. Three modes exist: slow and fast ion-acoustic modes and electron-acoustic mode. The occurrence of ESWs and their existence domain as a function of various plasma parameters, such as the number densities of ions and electron beam, the spectral index, κ, the electron beam velocity, the temperatures of ions, and electron beam, are analyzed. It is observed that both the slow and fast ion-acoustic modes support both positive and negative potential solitons as well as their coexistence. Further, they support a “forbidden gap,” the region in which the soliton ceases to propagate. In addition, slow ion-acoustic solitons support the existence of both positive and negative potential double layers. The electron-acoustic mode is only found to support negative potential solitons for parameters relevant to the lunar wake plasma. Fast Fourier transform of a soliton electric field produces a broadband frequency spectrum. It is suggested that all three soliton types taken together can provide a good explanation for the observed electrostatic waves in the lunar wake.

Occurrence of electrostatic solitary waves in the lunar wake

AbstractAn alternative generation mechanism for the electrostatic waves observed in the lunar wake during the first flyby of the Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission in terms of slow and fast ion‐acoustic and electron‐acoustic solitons is proposed. The lunar wake plasma is modeled by fluid multicomponent magnetized plasma comprising hot protons, hot heavier ions, α particles (He++), electron beam, and suprathermal electrons following kappa distribution. The electric fields associated with the slow and fast ion‐acoustic and electron‐acoustic solitons are in the range of ∼(0.0003–17) mV m−1. This is in excellent agreement with observed electrostatic wave electric field of 5 to 15 mV m−1. The fast Fourier transform of soliton electric fields generates broadband spectra having peak frequencies (corresponding to peak in the power spectra) in the range of ∼(3–1800) Hz. This corresponds to wave frequencies being in the range of ∼(0.001–0.56)fpe, where fpe is the electron plasma frequency. This matches well with the observed frequency range of (0.01–0.4) fpe. Further, the widths and velocities of these solitons are in the range ∼(100–8000) m and ∼(30–1300) km s−1, respectively. Both, soliton widths and velocities, match well with the estimated wavelengths (a few hundred meters to a couple of thousand meters) and estimated phase velocities (of the order of 1000 km s−1) of the electrostatic waves in the lunar wake.

Possible Ceres bow shock surfaces based on fluid models

AbstractThe hot electron beams that Dawn detected at Ceres can be explained by fast‐Fermi acceleration at a temporary bow shock. A shock forms when the solar wind encounters a temporary atmosphere, similar to a cometary coma. We use a magnetohydrodynamic model to quantitatively reproduce the 3‐D shock surface at Ceres and deduce the atmosphere characteristics that are required to create such a shock. Our most simple model requires about 1.8 kg/s, or 6 × 1025/s water vapor production rate to form such a shock. Such an estimate relies on characteristics of the solar wind‐Ceres interaction. We present several case studies to show how these conditions affect our estimate. In addition, we contrast these cases with the smaller and narrower shock caused by a subsurface induction. Our multifluid model reveals the asymmetry introduced by the large gyroradius of the heavy pickup ions and further constrains the IMF direction during the events.

Electron-acoustic solitary waves in a beam plasma with electron trapping and nonextensivity effects

A theoretical investigation is carried out for understanding the properties of electron-acoustic solitary waves (EASWs) in a beam plasma whose constituents are a cold beam electron fluid, hot nonextensive electrons obeying a vortex-like distribution with nonextensive factor q, and stationary ions. An energy integral (Schamel KdV) equation is derived by employing pseudo-potential (reductive perturbation) approach. The presence of nonextensive q-distributed hot trapped electrons and cold electron beam has been shown to influence the soliton structure quite significantly. The nonlinear dispersion relation is derived to analyze the dependency of the electron acoustic solitary wave quantities. From the analysis of our results, it is shown that the present plasma model supports the compressive EASWs. As the real plasma situations are observed with plasma species having a relative flow, so our present analysis should be useful for understanding the electrostatic solitary structures observed in the dayside auroral zone and other regions of the magnetosphere.

Propagation of a beam of hot electrons through solar wind plasma with generalized ( r , q ) $(r,q)$ distribution function

The background plasma is assumed to have generalized $(r, q)$ distribution for the electrons in the solar wind. The propagation of a beam of hot electrons through solar wind plasma with generalized $(r,q)$ distribution and the generation of Langmuir waves are simulated using quasilinear equations. It is shown that spectral indices $r$ and $q$ affect the quasilinear dynamics of the beam and Langmuir waves. The damping of beam generated waves increases in $(r,q)$ distributed plasma. As indices $r$ and $q$ increase the system shows quasilinear behavior which is more similar to the Maxwellian distribution function. The value of average velocity of the beam increases in a plasma with $(r, q)$ distribution function and as the values of $r$ and $q$ increase, the average velocity of the beam decreases. It is also shown that the gas-dynamical parameters of the beam are functions of spectral indices $r$ and $q$ . The upper boundary of the plateau, and local velocity spread are increasing functions while the lower boundary and height of plateau are decreasing functions of $r$ and $q$ . The local velocity shows smooth behavior with respect to spectral indices $r$ and $q$ , and for all indices at given time and position has approximately same values.

Transport and Energy Deposition of hot Electrons through the Shock Ignition pre Compressed Target

AbstractShock ignition as an alternative scheme of the laser fusion has the potential of achieving efficient implosion. However, hot electrons produced in result of ignitor‐corona interaction may penetrate deep into the fuel making the compression less effective. Transport and energy deposition of hot electron beam into the dense pre compressed of HiPER target by means of Monte Carlo approach are discussed considering the influence of real density and electron beam characteristics. The target parameters before igniting the hot spot have been extracted from a fluid code and used as the initial profile for Monte Carlo simulations. In comparison with simplified step like density profile, electrons penetrate slightly deeper in the case of real shaped density profile. In addition, deposition zone of a broad spectrum electron beam is wider while, monoenergetic electrons depose their energy locally resulting more maximum energy deposition value. (© 2016 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Studies of high energy density physics and laboratory astrophysics driven by intense lasers

Laser plasmas are capable of creating unique physical conditions with extreme high energy density, which are not only closely relevant to inertial fusion energy studies, but also to laboratory simulation of some astrophysical processes. In this paper, we highlight some recent progress made by our research teams. The first part is about directional hot electron beam generation and transport for fast ignition of inertial confinement fusion, as well as a new scheme of fast ignition by use of a strong external DC magnetic field. The second part concerns laboratory modeling of some astrophysical phenomena, including 1) studies of the topological structure of magnetic reconnection/annihilation that relates closely to geomagnetic substorms, loop-top X-ray source and mass ejection in solar flares, and 2) magnetic field generation and evolution in collisionless shock formation.

Magnetized Fast ignition (MFI) and Laser Plasma Interactions in Strong Magnetic Field

In this paper, magnetized fast ignition (MFI) is proposed for improving the coupling efficiency of a heating laser to a core plasma. In the MFI, the external magnetic field is applied to reduce the hot electron energy and focus the dense hot electron flux to the core. The external magnetic field higher than 100T is generated by the laser driven coil and it is amplified by the implosion. The magnetic field at the tip of the cone is expected to reach higher than 10kT and the laser plasma interaction and the hot electron transport are modified. As the results of applying the external magnetic field, hot electron energy is reduced to less than 5MeV for the laser intensity of 1020W/ cm2 and the Weibel instability is suppressed to collimate the hot electron beam to the core.

Production and characterization of thin film group IIIB, IVB and rare earth hydrides by reactive evaporation

A recent short history of reactive evaporation by D. M. Mattox [History Corner—A Short History of Reactive Evaporation, SVC Bulletin (Society of Vacuum Coaters, Spring 2014), p. 50–51] describes various methods for producing oxides, nitrides, carbides, and some compounds, but hydrides were not mentioned. A study was performed in the mid-1970s at the General Electric Company Neutron Devices Department in Largo, FL, by the author to study preparation of thin film hydrides using reactive evaporation and to determine their unique characteristics and properties. Films were produced of scandium (Sc), yttrium (Y), titanium (Ti), zirconium (Zr), and the rare earth praseodymium (Pr), neodymium (Nd), gadolinium (Gd), dysprosium (Dy), and erbium (Er) hydrides by hot crucible filament and electron beam evaporation in atmospheres of deuterium and tritium gases. All-metal vacuum systems were used and those used with tritium were dedicated for this processing. Thin film test samples 1000 nm thick were prepared on 1.27 cm diameter molybdenum disk substrates for each occluder (i.e., an element that can react with hydrogen to form a hydride) material. Loading characteristics as determined by gas-to-metal atomic ratios, oxidation characteristics as determined by argon–sputter Auger analysis, film structure as determined by scanning electron microscope analysis, and film stress properties as determined by a double resonator technique were used to define properties of interest. Results showed hydrogen-to-metal atomic ratios varied from 1.5 to 2.0 with near maximum loading for all but Pr and Nd occluders which correlated with the oxidation levels observed, with all occluder oxidation levels being variable due to vacuum system internal processing conditions and the materials used. Surface oxide levels varied from ∼80 Å to over 1000 Å. For most films studied, results showed that a maximum loading ratio of near 2.0 and a minimum surface oxide level of ∼80 Å could be obtained with a bulk film oxygen level of ∼0.54 oxygen as determined by microprobe analysis when an evaporation rate of ∼0.313 mg/cm2 min was used in an atmosphere of D2 or T2 gas at a system deposition pressure of 1 × 10−3 Torr (1.33 × 10−1 Pa) in an evaporation time of ∼2 min. Platelet type (i.e., a film microstructure showing an overlay of flat plates with large grain sizes) film structures were observed for most films with some film mechanical properties determined (i.e., grain size and Vickers μ-hardness), and reduced stress levels were seen with initial normalized differential (tensile) stress levels being (1.0–4.0) × 108 dyne/cm2 for tritium loaded samples and (1.5 ± 0.5) × 109 dyne/cm2 for deuterium loaded samples. Also, stress aging characteristics were determined for some hydride films prepared in a radioactive tritium gas atmosphere. Tritium loading, however, had the undesirable characteristic of having to dispose of the internal processing system fixtures, which can be minimized, but the reactive evaporation technique produced desirable thin films.

Weldability of 9Cr-ODS and JLF-1 Steels for Dissimilar Joining with Hot Isostatic Pressing and Electron Beam Welding

Weldability of 9Cr-ODS and JLF-1 Steels for Dissimilar Joining with Hot Isostatic Pressing and Electron Beam Welding