Hot Electron Beam Research Articles

Effect of electron beam on the properties of electron-acoustic rogue waves

The properties of nonlinear electron-acoustic rogue waves have been investigated in an unmagnetized collisionless four-component plasma system consisting of a cold electron fluid, Maxwellian hot electrons, an electron beam and stationary ions. It is found that the basic set of fluid equations is reduced to a nonlinear Schrodinger equation. The dependence of rogue wave profiles and the associated electric field on the carrier wave number, normalized density of hot electron and electron beam, relative cold electron temperature and relative beam temperature are discussed. The results of the present investigation may be applicable in auroral zone plasma.

Electron Beam Reduction Method for Preparing the Catalyst Layer in the Growth of Carbon Nanotubes

In this paper, electron beam (e-beam) reduction method is applied for the catalyst layer preparation in the growth of carbon nanotubes (CNTs). A hot cathodic electron beam facility was employed to electron bombarding of catalyst layer before stage of CNTs growth. This new method leads to reducing the diameter of particles via sputtering and evaporating the surface of catalyst. The growth of CNTs was performed on the Fe catalyst layer with SiO2 substrate in an environment of different mixed gases (H2, NH3 and C2H2) by thermal chemical vapor deposition (TCVD) system. The morphology of the electron beam reduced catalyst particles were probed by atomic force microscopy (AFM). All samples were analyzed by scanning electron microscopy (SEM) before and after growth of CNTs. SEM analyses clarified that the catalyst grains have been smaller under effect of electron beam bombardment.

STUDY OF WHISTLER MODE WAVE BY INJECTION OF RELATIVISTIC HOT ELECTRONS BEAM IN THE MAGNETOSPHERE OF URANUS

In present paper, the efiect of relativistic hot electron beam for fleld aligned Whistler mode waves has been studied theoretically in the presence of AC electric fleld perpendicular to magnetic fleld. Studies have been performed using perturbative approach along with the method of characteristic solutions and are valid for comparatively small ambient magnetic fleld 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 efiective 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 signiflcantly 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.

Collimation of hot electron beams by external field from magnetic-flux compression

AbstractIn fast ignition of inertial confinement fusion, hot electron beam is considered to be an appropriate energy source for ignition. However, hot electrons are divergent as they are transporting in over-dense plasma. So collimating the hot electrons becomes one of the most important issues in fast ignition. A method to collimate hot electron beam by external magnetic field is proposed in this paper. The external field can be generated by compressing a seed magnetic field at the stage of laser-driven implosion. This method is confirmed by particle-in-cell simulations. The results show that hot electrons are well collimated by external magnetic field from magnetic-flux compression.

Simulation study of collisional effects on the propagation of a hot electron beam and generation of Langmuir turbulence for application in type III radio bursts

AbstractThe propagation of a localized beam (cloud) of hot electrons and generation of Langmuir waves are investigated using numerical simulation of the quasi-linear equations in the presence of collisional effects for electrons and beam-driven Langmuir waves. It is found that inclusion of the collisional damping of Langmuir waves has remarkable effects on the evolution of the electron distribution function and the spectral density of Langmuir waves, while the effect of collision term for electrons is almost negligible. It is also found that in the presence of collisional damping of Langmuir waves, the relaxation of the beam distribution function in velocity space is retarded and the Langmuir waves are strongly suppressed. The average propagation velocity of the beam is not constant and is larger when collisional damping of Langmuir waves is considered. The collisional damping for electrons does not affect the upper boundary of the plateau but the collisional damping of Langmuir waves pushes it towards small velocities. It is also found that the local velocity of the beam and its width decrease when the collisional damping of Langmuir waves is included.

Coherent transition radiation in relativistic laser–solid interactions

Coherent transition radiation (CTR) produced by the hot electrons generated when solid targets are irradiated by high-intensity lasers is examined. The theory is extended to include the effects of collisions on the generated hot electron beam. The collisional effects on electron transport, blooming and straggling, leads to transverse and longitudinal loss of coherence of the electron beam structure, resulting in a decrease in efficiency in the CTR. The directionality of the electrons leads to measurable non-radial components for the polarization of the CTR. With these effects accounted for, the properties of this radiation can give valuable information on the high-energy tail of the fast electrons produced at the target front side and transported through the solid-density material, such as temperature, direction and size of the filaments composing the beam.

Langmuir turbulence and quasilinear interactions of a hot electron beam in the inhomogeneous solar corona plasma with a uniform electric field

Using numerical simulation of the quasilinear equations, the propagation of an electron beam through inhomogeneous solar corona plasma and generation of Langmuir waves are investigated by taking into account a uniform electric field. The level of the excited Langmuir waves is remarkably enhanced by decreasing density and the applied electric field. The mean velocity of propagation of the beam is not a constant and decreases with distance from the injection point. The effect of the electric field is more pronounced on the slow electrons and accelerates them to high velocity region while the density gradient mainly affects the fast electrons and effectively decelerates them.

Beam propagation and Langmuir wave generation in a plasma with κ distribution function

Using a kappa velocity distribution function for the electrons of the background plasma, the dynamics of a beam of hot electrons streaming through the plasma and the generation of Langmuir waves are investigated in the frame work of quasilinear theory. It is shown that the Langmuir waves are strongly damped by high energy tail of the Kappa distribution function. The spatial expansion of the beam is reduced and the spectral density of Langmuir waves becomes narrower. The height of the plateau in the beam distribution function increases at small velocities and the average velocity of beam is larger than that of a Maxwellian distribution. The influence of Kappa velocity distribution function on the gasdynamical parameters is investigated. It is found that, the height of plateau in the beam distribution function, and its lower velocity boundary are enhanced while, the local beam width in velocity space decreases.

YBCO-Film Based FIR Detectors in Not Dissipative Regime: Local THz Response by Heavy-Ion Nanostructure Implantation

Broadband electromagnetic characterization of hot plasmas and electron beams requires real-time, direct detection of high flux of electromagnetic radiation. We report about a project aimed at creating robust THz detectors based on YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-x</sub> (YBCO) films, working around liquid nitrogen temperature and in a regime of low dissipation. The sensor layout mainly consists in two contiguous meanders that are integrated on the same substrate. One of them is nanostructured by local high-energy heavy-ion irradiation; the other one (as-grown YBCO) is used for thermo-electric signal reference. By measuring the voltage response to THz excitation of YBCO film, at a given bias current and temperature, on selected substrates (Yttria Stabilized Zirconia (YSZ) and MgO), it turns out that only the nanostructured part is brought in the dissipative state when exposed to THz radiation. We present estimated noise equivalent power and relaxation times for YBCO grown on YSZ and on MgO substrates. On the latter, we experimentally checked out the device response to time-varying Far-Infrared (FIR) signals up to 800 Hz. The proposed device turns out to fit the necessary requirements for measurement of electron cyclotron emission of hot plasmas or of electron beams in the FIR spectrum.

Effect of Electron Beam Bombarding of the Catalyst Layer on the Growth of Carbon Nanostructures by TCVD Method

The growth behavior of carbon nanotubes (CNTs) grown on electron bombarded catalyst layer has been investigated in this paper. A hot cathodic electron beam facility was employed to electron bombarding of catalyst layer before stage of CNTs growth. The growth of carbon nanotubes was performed on the Fe catalyst layer with sio2 substrate in an environment of different mixed gases (H2, NH3 and C2H2) by Thermal Chemical Vapor Deposition (TCVD) system. The pretreated substrates were probed by Atomic Force Microscopy (AFM) and CNTs grown was confirmed by Raman spectroscopy. Moreover, all samples were analyzed by Scanning Electron Microscopy (SEM) before and after growth of CNTs. SEM analyzes clarified that the catalyst grains has been smaller under effect of electron beam bombardment.

Materials development for ITER shielding and test blanket in China

China is a member of the ITER program and is developing her own materials for its shielding and test blanket modules. The materials include vacuum-hot-pressing (VHP) Be, CuCrZr alloy, 316L(N) and China low activation ferritic/martensitic (CLF-1) steels. Joining technologies including Be/Cu hot isostatic pressing (HIP) and electron beam (EB) weldability of 316L(N) were investigated. Chinese VHP-Be showed good properties, with BeO content and ductility that satisfy the ITER requirements. Be/Cu mock-ups were fabricated for Be qualification tests at simulated ITER vertical displacement event (VDE) and heat flux cycling conditions. Fine microstructure and good mechanical strength of the CuCrZr alloy were achieved by a pre-forging treatment, while the weldability of 316L(N) by EB was demonstrated for welding depths varying from 5 to 80mm. Fine microstructure, high strength, and good ductility were achieved in CLF-1 steel by an optimized normalizing, tempering and aging procedure.

Generation and optimization of electron currents along the walls of a conical target for fast ignition

The interaction of an ultraintense laser pulse with a conical target is studied by means of numerical particle-in-cell simulations in the context of fast ignition. The divergence of the fast electron beam generated at the tip of the cone has been shown to be a crucial parameter for the efficient coupling of the ignition laser pulse to the precompressed fusion pellet. In this paper, we demonstrate that a focused hot electron beam is produced at the cone tip, provided that electron currents flowing along the surfaces of the cone sidewalls are efficiently generated. The influence of various interaction parameters over the formation of these wall currents is investigated. It is found that the strength of the electron flows is enhanced for high laser intensities, low density targets, and steep density gradients inside the cone. The hot electron energy distribution obeys a power law for energies of up to a few MeV, with the addition of a high-energy Maxwellian tail.

An ion acceleration mechanism in laser illuminated targets with internal electron density structure

1D and 2D PIC simulations of light ion acceleration by irradiation of structured thin foils by short pulse, high intensity lasers have been performed. When the back coating material is thicker than the typical scale length for TNSA fields the ion energy spectra contain peaks. These peaks are found to be due to the acceleration of ions by an electric field which builds up at internal interfaces between materials with different electron number densities. The electric field is generated by incomplete neutralization of the charge built up at the head of the hot electron beam as it crosses the interface between the two materials. In these simulations the back material layer is sufficiently thick that the sheath field drops to zero before reaching the vacuum boundary. The acceleration responsible for the peaks is therefore from within the material and is superimposed on the normal TNSA acceleration from the back material–vacuum surface, i.e. there are two distinct sites of particle acceleration. It is possible that this mechanism may explain features previously observed in simulations. A comparison is also made with experiments with thick rear coatings.

Anomalous momentum transport in astrophysical return-current beam plasmas - the two-dimensional electromagnetic case

AbstractAnomalous momentum transport in a typical astrophysical return-current beam plasma system is studied by means of two-dimensional PIC code simulations. A forward going hot electron beam compensated by a cold return beam is considered. A linear dispersion analysis predicts the linerarly unstable wave modes. Our simulation reveals that the nonlinerly generated waves and the consequent wave-particle interactions cause the electron heating and the relaxation of the electron drifts. Both, the developments of electrostatic and electromagnetic waves are analyzed as well as the roles they play in energy conversion. In particular it is found that the relaxation of electron drifts is stronger if the electromagnetic turbulence is taken into account.

Magnetic collimation of petawatt driven fast electron beam for prospective fast ignition studies

Collimated transport of fast electron beam through solid density matter is one of the key issues behind the success of the fast ignition scheme by means of which the required amount of ignition energy can be delivered to the hot spot region of the compressed fuel. Here we report on a hot electron beam collimation scheme in solids by tactfully using the strong magnetic fields generated by an electrical resistivity gradient according to Faraday's law. This was accomplished by appropriately fabricating the targets in such a way that the electron beam is directed to flow in a metal which is embedded in a much lower resistivity and atomic number metal. Experimental results showed guided transport of hot electron beam over hundreds of microns length inside solid density plasma, which were obtained from two experiments examining the scheme for petawatt laser driven hot electron beam while employing various target configurations.

Development of Infrared Ray Curing Technology at Continuous Coil Coating Line

The No. 1 continuous coil coating line of Dongbu Steel produces 70,000 tons of commercial quality products annually, and the pre-coated metal (PCM) products are widely used for a home appliances or building materials. The lines are consisted of pre-treatment, painting, curing and tension levelling processes. The typical curing methods are injection of hot air, infrared rays, electron beam, or induction heated oven. Peak metal temperature (PMT) is the vital factor that determines the product quality. The curing oven of No. 1 continuous coil coating line revamped from injection of hot air to infrared rays type and operated from 2007. A PMT setup model was developed for control the strip temperature, and applied in site, and systemized. The operation results showed that the accuracy of the setup model achieved above 96% consistently.

Characterization of two distinct, simultaneous hot electron beams in intense laser-solid interactions

The transport of energetic electron beams generated from aluminum foils irradiated by ultraintense laser pulses has been studied by imaging coherent transition radiation from the rear side of the target. Two distinct beams of MeV electrons are emitted from the target rear side at the same time. This measurement indicates that two different mechanisms, namely resonance absorption and jxB heating, accelerate the electrons at the targets front side and drive them to different directions, with different temperatures. This interpretation is consistent with 3D-particle-in-cell simulations.

Dynamics of a beam of hot electrons propagating through a plasma in the presence of nonthermal electrons

The dynamics of a beam of hot electrons traveling through a cold plasma and the generation of Langmuir waves are investigated in the presence of a nonthermal tail of electrons in the background distribution function. Using quasilinear simulations, it is shown that in the presence of the nonthermal electrons, the relaxation of the beam distribution function in velocity space is retarded and the Langmuir waves are strongly damped at low velocities. The average velocity of beam propagation is almost constant but its magnitude is larger in the presence of nonthermal electrons than their absence. It is found that the self-similarity of the system is preserved in the presence of nonthermal electrons. The effects of nonthermal electrons on the evolution of gas-dynamical parameters of the beam, including the height of plateau in the beam distribution function, its upper and lower velocity boundaries, and beam velocity width, are also studied. It is found that initially the values of the upper and lower velocity boundaries are almost unaltered, but at large times the lower (upper) boundary velocity is larger (smaller) in the presence of nonthermal electrons than without the nonthermal electrons.

Integrated simulations of implosion, electron transport, and heating for direct-drive fast-ignition targets

A thorough understanding of future integrated fast-ignition experiments combining compression and heating of high-density thermonuclear fuel requires hybrid (fluid+particle) simulations of the implosion and ignition process. Different spatial and temporal scales need to be resolved to model the entire fast-ignition experiment. The two-dimensional (2D) axisymmetric hydrocode DRACO [P. B. Radha et al., Phys. Plasmas 12, 056307 (2005)] and the 2D/three-dimensional hybrid particle-in-cell code LSP [D. R. Welch et al., Nucl. Instrum. Methods Phys. Res. A 464, 134 (2001)] have been integrated to simulate the implosion and heating of direct-drive, fast-ignition fusion targets. DRACO includes the physics required to simulate compression, ignition, and burn of fast-ignition targets. LSP simulates the transport of hot electrons from the place where they are generated to the dense fuel core where their energy is absorbed. The results from integrated simulations of cone-in-shell CD targets designed for fast-ignition experiments on OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997); C. Stoeckl et al., Fusion Sci. Technol. 49, 367 (2006)] are presented. Target heating and neutron yields are computed. The results from LSP simulations of electron transport in solid-density plastic targets are also presented. They confirm an increase in the electron divergence angle with the laser intensity in the current experiments. The self-generated resistive magnetic field is found to collimate the hot-electron beam and increase the coupling efficiency of hot electrons with the target. Resistive filamentation of the hot-electron beam is also observed.

Study of ultraintense laser propagation in overdense plasmas for fast ignition

Laser plasma interactions in a relativistic regime relevant to the fast ignition in inertial confinement fusion have been investigated. Ultraintense laser propagation in preformed plasmas and hot electron generation are studied. The experiments are performed using a 100 TW 0.6 ps laser and a 20 TW 0.6 ps laser synchronized by a long pulse laser. In the study, a self-focused ultraintense laser beam propagates along its axis into an overdense plasma with peak density 1022/cm3. Channel formation in the plasma is observed. The laser transmission in the overdense plasma depends on the position of its focus and can take place in plasmas with peak densities as high as 5×1022/cm3. The hot electron beams produced by the laser-plasma interaction have a divergence angle of ∼30°, which is smaller than that from laser-solid interactions. For deeper penetration of the laser light into the plasma, the use of multiple short pulse lasers is proposed. The latter scheme is investigated using particle-in-cell simulation. It is found that when the pulse duration and the interval between the pulses are appropriate, the laser pulse train can channel into the plasma deeper than a single longer pulse laser of similar peak intensity and total energy.