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On The Origin Of Super Hot Electrons In Intense Laser Plasma Interactions
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Book Synopsis On the Origin of Super-hot Electrons in Intense Laser-plasma Interactions by : Andrew G. Krygier
Download or read book On the Origin of Super-hot Electrons in Intense Laser-plasma Interactions written by Andrew G. Krygier and published by . This book was released on 2013 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: This thesis investigates the ultraintense laser-plasma interaction. An experiment to measure the generation of relativistic electrons and positrons was performed at the Texas Petawatt laser which resulted in the observation of the highest known positron energies ever recorded. The positrons are created by the Bethe-Heitler process where an electron scatters and emits bremsstrahlung radiation which then interacts with an atomic nucleus and creates an electron-positron pair. The positron bunch is a useful diagnostic for understanding the laser-plasma interaction. Modeling results are also presented that describe the acceleration mechanism for the highest energy electrons which drive many important applications. A simple mechanism we call loop-injected direct acceleration that is found to be overwhelmingly dominant in the acceleration of super-hot electrons is discussed in detail.
Book Synopsis Frontiers in High Energy Density Physics by : National Research Council
Download or read book Frontiers in High Energy Density Physics written by National Research Council and published by National Academies Press. This book was released on 2003-05-11 with total page 177 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent scientific and technical advances have made it possible to create matter in the laboratory under conditions relevant to astrophysical systems such as supernovae and black holes. These advances will also benefit inertial confinement fusion research and the nation's nuclear weapon's program. The report describes the major research facilities on which such high energy density conditions can be achieved and lists a number of key scientific questions about high energy density physics that can be addressed by this research. Several recommendations are presented that would facilitate the development of a comprehensive strategy for realizing these research opportunities.
Book Synopsis On the Acceleration and Transport of Electrons Generated by Intense Laser-Plasma Interactions at Sharp Interfaces by : Joshua Joseph May
Download or read book On the Acceleration and Transport of Electrons Generated by Intense Laser-Plasma Interactions at Sharp Interfaces written by Joshua Joseph May and published by . This book was released on 2017 with total page 250 pages. Available in PDF, EPUB and Kindle. Book excerpt: The continued development of the chirped pulse amplification technique has allowed for the development of lasers with powers of in excess of $10^{15}W$, for pulse lengths with durations of between .01 and 10 picoseconds, and which can be focused to energy densities greater than 100 giga-atmospheres. When such lasers are focused onto material targets, the possibility of creating particle beams with energy fluxes of comparable parameters arises. Such interactions have a number of theorized applications. For instance, in the Fast Ignition concept for Inertial Confinement Fusion \cite{Tabak:1994vx}, a high-intensity laser efficiently transfers its energy into an electron beam with an appropriate spectra which is then transported into a compressed target and initiate a fusion reaction. Another possible use is the so called Radiation Pressure Acceleration mechanism, in which a high-intensity, circularly polarized laser is used to create a mono-energetic ion beam which could then be used for medical imaging and treatment, among other applications. For this latter application, it is important that the laser energy is transferred to the ions and not to the electrons. However the physics of such high energy-density laser-matter interactions is highly kinetic and non-linear, and presently not fully understood. In this dissertation, we use the Particle-in-Cell code OSIRIS \cite{Fonseca:2002, Hemker:1999} to explore the generation and transport of relativistic particle beams created by high intensity lasers focused onto solid density matter at normal incidence. To explore the generation of relativistic electrons by such interactions, we use primarily one-dimensional (1D) and two-dimensional (2D), and a few three-dimensional simulations (3D). We initially examine the idealized case of normal incidence of relatively short, plane-wave lasers on flat, sharp interfaces. We find that in 1D the results are highly dependent on the initial temperature of the plasma, with significant absorption into relativistic electrons only possible when the temperature is high in the direction parallel to the electric field of the laser. In multi-dimensions, absorption into relativistic electrons arises independent of the initial temperature for both fixed and mobile ions, although the absorption is higher for mobile ions. In most cases however, absorption remains at $10's$ of percent, and as such a standing wave structure from the incoming and reflected wave is setup in front of the plasma surface. The peak momentum of the accelerated electrons is found to be $2 a_0 m_e c$, where $a_0 \equiv e A_0/m_e c^2$ is the normalized vector potential of the laser in vacuum, $e$ is the electron charge, $m_e$ is the electron mass, and $c$ is the speed of light. We consider cases for which $a_0>1$. We therefore call this the $2 a_0$ acceleration process. Using particle tracking, we identify the detailed physics behind the $2 a_0$ process and find it is related to the standing wave structure of the fields. We observe that the particles which gain energy do so by interacting with the laser electric field within a quarter wavelength of the surface where it is at an anti-node (it is a node at the surface). We find that only particles with high initial momentum -- in particular high transverse momentum -- are able to navigate through the laser magnetic field as its magnitude decreases in time each half laser cycle (it is an anti-node at the surface) to penetrate a quarter wavelength into the vacuum where the laser electric field is large. For a circularly polarized laser the magnetic field amplitude never decreases at the surface, instead its direction simply rotates. This prevents electrons from leaving the plasma and they therefore cannot gain energy from the electric field. For pulses with longer durations ($\gtrsim 250fs$), or for plasmas which do not have initially sharp interfaces, we discover that in addition to the $2 a_0$ acceleration at the surface, relativistic particles are also generated in an underdense region in front of the target. These particles have energies without a sharp upper bound. Although accelerating these particles removes energy from the incoming laser, and although the surface of the plasma does not stay perfectly flat and so the standing wave structure becomes modified, we find in most cases, the $2 a_0$ acceleration mechanism occurs similarly at the surface and that it still dominates the overall absorption of the laser. To explore the generation of relativistic electrons at a solid surface and transport of the heat flux of these electrons in cold or warm dense matter, we compare OSIRIS simulations with results from an experiment performed on the OMEGA laser system at the University of Rochester. In that experiment, a thin layer of gold placed on a slab of plastic is illuminated by an intense laser. A greater than order-of-magnitude decrease in the fluence of hot electrons is observed when those electrons are transported through a plasma created from a shock-heated plastic foam, as compared to transport through cold matter (unshocked plastic foam) at somewhat higher density. Our simulations indicate two reasons for the experimental result, both related to the magnetic field. The primary effect is the generation of a collimating B-field around the electron beam in the cold plastic foam, caused by the resistivity of the plastic. We use a Monte Carlo collision algorithm implemented in OSIRIS to model the experiment. The incoming relativistic electrons generate a return current. This generates a resistive electric field which then generates a magnetic field from Faraday's law. This magnetic field collimates the forward moving relativistic electrons. The collisionality of both the plastic and the gold are likely to be greater in the experiment than the 2D simulations where we used a lower density for the gold (to make the simulations possible) which heats up more. In addition, the use of 2D simulations also causes the plastic to heat up more than expected. We compensated for this by increasing the collisionality of the plasma in the simulations and this led to better agreement. The second effect is the growth of a strong, reflecting B-field at the edge of the plastic region in the shock heated material, created by the convective transport of this field back towards the beam source due to the neutralizing return current. Both effects appear to be caused primarily by the difference is density in the two cases. Owing to its higher heat capacity, the higher density material does not heat up as much from the heat flux coming from the gold, which leads to a larger resistivity. Lastly, we explored a numerical effect which has particular relevance to these simulations, due to their high energy and plasma densities. This effect is caused by the use of macro particles (which represent many real particles) which have the correct charge to mass ratio but higher charge. Therefore, any physics of a single charge that scales as $q^2/m$ will be artificially high. Physics that involves scales smaller than the macro-particle size can be mitigated through the use of finite size particles. However, for relativistic particles the spatial scale that matters is the skin depth and the cell sizes and particle sizes are both smaller than this. This allows the wakes created by these particles to be artificially high which causes them to slow down much faster than a single electron. We studied this macro-particle stopping power theoretically and in OSIRIS simulations. We also proposed a solution in which particles are split in to smaller particles as they gain energy. We call this effect Macro Particle Stopping. Although this effect can be mitigated by using more particles, this is not always computationally efficient. We show how it can also be mitigated by using high-order particle shapes, and/or by using a particle-splitting method which reduces the charge of only the most energetic electrons.
Book Synopsis Atoms, Solids, and Plasmas in Super-Intense Laser Fields by : Dimitri Batani
Download or read book Atoms, Solids, and Plasmas in Super-Intense Laser Fields written by Dimitri Batani and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 409 pages. Available in PDF, EPUB and Kindle. Book excerpt: The recent developement of high power lasers, delivering femtosecond pulses of 20 2 intensities up to 10 W/cm , has led to the discovery of new phenomena in laser interactions with matter. At these enormous laser intensities, atoms, and molecules are exposed to extreme conditions and new phenomena occur, such as the very rapid multi photon ionization of atomic systems, the emission by these systems of very high order harmonics of the exciting laser light, the Coulomb explosion of molecules, and the acceleration of electrons close to the velocity of light. These phenomena generate new behaviour of bulk matter in intense laser fields, with great potential for wide ranging applications which include the study of ultra-fast processes, the development of high-frequency lasers, and the investigation of the properties of plasmas and condensed matter under extreme conditions of temperature and pressure. In particular, the concept of the "fast ignitor" approach to inertial confinement fusion (ICF) has been proposed, which is based on the separation of the compression and the ignition phases in laser-driven ICF. The aim of this course on "Atom, Solids and Plasmas in Super-Intense Laser fields" was to bring together senior researchers and students in atomic and molecular physics, laser physics, condensed matter and plasma physics, in order to review recent developments in high-intensity laser-matter interactions. The course was held at the Ettore Majorana International Centre for Scientific Culture in Erice from July 8 to July 14,2000.
Book Synopsis Laser-plasma Interactions and Hot Electron Generation in Inertial Confinement Fusion by : Jun Li
Download or read book Laser-plasma Interactions and Hot Electron Generation in Inertial Confinement Fusion written by Jun Li and published by . This book was released on 2016 with total page 101 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis studies several problems related to hot (energetic) electron generation in laser-plasma interactions in inertial confinement fusion (ICF). We study laserplasma instabilities (LPI) that can generate hot electrons in direct drive ICF under a range of laser intensities relevant to both the conventional hot-spot ignition and shock ignition. We study the in uence of LPI and hot electrons on the hydrodynamic evolution of ICF targets. We study hot electron generation in intense laser-plasma interactions in fast ignition cone targets. We also study how to implement particle collisions, which are important to hot electron generation in LPI, in Particle-in-Cell (PIC) codes on Graphic Process Units (GPU's). We find that ion density modulations can turn convective two-plasmon decay (TPD) and stimulated Raman scattering (SRS) instabilities to absolute ones in the region below the quarter critical density (nc=4). In this region, our uid simulations show that when a sinusoidal density modulation is superimposed on a linear density profile, convective two-plasmon decay (TPD) and stimulated Raman scattering (SRS) instabilities can become absolutely unstable under realistic direct-drive ICF conditions. Analysis of a three-wave model with a two-slope density profile shows that a sufficiently large change of the density gradient in a linear density profile can turn convective instabilities into absolute ones. An analytical expression is given for the threshold of the gradient change, which depends on the convective gain only. Growth rates for the absolute modes are also obtained. The threshold and growth rates from the two-slope profile are found to approximate those under sinusoidal modulations. These results explain the origin of the TPD modes below the nc=4 surface that in previous research were found to be critical to hot electron generation. Combining PIC and hydrodynamics simulations, we study the LPI and hydro evolution of coronal plasmas in an OMEGA EP[J.H. Kelly et al., 2006] long-scalelength experiment[Hu et al., 2013; Haberberger et al., 2014] with planar targets. Plasma and laser conditions are first obtained in a DRACO hydro simulation with only inverse-bremsstrahlung absorption. Using these conditions, an OSIRIS PIC simulation is performed to study laser absorption and hot-electron generation caused by LPI near the nc=4 region. The obtained information from the PIC simulation is subsequently coupled back to another DRACO simulation to examine how the LPI affect the overall hydrodynamics. The results show that the LPIinduced laser absorption can increase the electron temperature due to local heating by plasma waves. But it does not significantly change the density scale length in the corona because the high heat conductivity can spread the higher energy deposited near the nc=4 region in a wider region, and the portion of the energy carried by the hot electrons going towards high density region is still deposited beyond the nc=4 region. The collisional effects can affect the hot electron generation by damping the coupling waves of TPD and SRS instabilities. We have benchmarked the collision package in OSIRIS and adapted this package to a PIC code on graphics processors (GPU) with CUDA. The collision package is based on the cumulative collision theory, which treats a succession of small-angle binary collisions as a unique binary collision with a large scattering angle. It uses the computing cell in the GPUPIC code as the collision cell, and randomly pairs the particles in each collision cell for collision. In this process, it takes advantage of the fast on-chip shared memory and gets a remarkable performance. The benchmarks show that this collision package only needs to be called every 100 steps, and has a performance of 0:07 - 0:09ns=particle - step, only a 1:4% increase over the 5:36ns=particle - step without collisions on a Nvidia GTX 680 GPU. Test problems of beam-plasma scattering and electron plasma wave damping show that the collision frequencies calculated from the simulation results are consistent with theory. Hot electron generation is also important in fast ignition where typical laser intensities are higher than the hot-spot ignition or shock ignition. We perform PIC simulations for a cone-in-shell integrated fast-ignition experiment at the Omega Laser Facility[Boehly et al., 1997] with the initial plasma density profile taken from hydrodynamic simulations of the prepulse interaction with the gold cone. Hotelectron generation from laser-pre-plasma interactions and transport up to 100nc are studied. The simulations show a mean divergence half-angle of 68 degrees and 50% absorption for the hot electrons. The results show that the hot electrons are dominated in number by low-energy electrons but in energy by multi-MeV electrons. Electron transport between 5 and 100 nc is ballistic. In the late stage of the simulation, hot electron generation is largely independent of polarization, indicating a stochastic hot-electron-generation mechanism.
Book Synopsis Sources of Hot Electrons in Laser-plasma Interaction with Emphasis on Raman and Turbulence Absorption by :
Download or read book Sources of Hot Electrons in Laser-plasma Interaction with Emphasis on Raman and Turbulence Absorption written by and published by . This book was released on 1982 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Heating targets with high power lasers results in a sizable fraction of the absorbed energy going into electrons of temperature much greater than thermal which can pre-heat the pellet core and accelerate fast ion blowoff which results in poor momentum transfer and hence poor compression efficiency. The present emphasis is to build lasers of higher frequency, .omega.0, which at the same W/cm2 results in more absorption into cooler electrons. Two physical reasons are that the laser can propagate to a higher electron density, n, infinity.omega.02 resulting in more collisional inverse bremsstrahlung absorption proportional to n, and because the hot temperatures from some plasma absorption processes increase as the oscillatory velocity of an electron in the laser electric field v0/c = eE/(m/sub e/.omega.0). The heated electron temperatures from other plasma processes (Raman for example approx.(m/sub e//2)v2/sub phase/ and the higher laser frequency helps by increasing the competing collisional absorption and decreasing the Raman gain.
Book Synopsis Target Surface Area Effects on Hot Electron Dynamics from High Intensity Laser–plasma Interactions by :
Download or read book Target Surface Area Effects on Hot Electron Dynamics from High Intensity Laser–plasma Interactions written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Study of Relativistic Electrons Generated from Ultra-intense Laser-plasma Interaction Relevant to Laser Wakefield Acceleration and Fast Ignition Laser Fusion by : Mianzhen Mo
Download or read book Study of Relativistic Electrons Generated from Ultra-intense Laser-plasma Interaction Relevant to Laser Wakefield Acceleration and Fast Ignition Laser Fusion written by Mianzhen Mo and published by . This book was released on 2015 with total page 283 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ultra-intense (> 10^18 W/cm^2) laser interaction with matter is capable of producing relativistic electrons which have a variety of applications in scientific and medical research. Knowledge of various aspects of these hot electrons is important in harnessing them for various applications. Of particular interest for this thesis is the investigation of hot electrons generated in the areas of Laser Wakefield Acceleration (LWFA) and Fast Ignition (FI). LWFA is a physical process in which electrons are accelerated by the strong longitudinal electrostatic fields that are formed inside the plasma cavities or wakes produced by the propagation of an ultra-intense laser pulse through an under-dense plasma. The accelerating E-fields inside the cavities are 1000 times higher than those of conventional particle accelerators and can accelerate electrons to the relativistic regime in a very short distance, on the order of a few millimeters. In addition, Betatron X-ray radiation can be produced from LWFA as a result of the transverse oscillations of the relativistic electrons inside the laser wakefield driven cavity. The pulse duration of Betatron radiation can be as short as a few femtoseconds, making it an ideal probe for measuring physical phenomena taking place on the time scale of femtoseconds. Experimental research on the electron acceleration of the LWFA has been conducted in this thesis and has led to the generation of mono-energetic electron bunches with peak energies ranging from a few hundreds of MeV to 1 GeV. In addition, the Betatron radiation emitted from LWFA was successfully characterized based on a technique of reflection off a grazing incidence mirror. Furthermore, we have developed a Betatron X-ray probe beamline based on the technique of K-shell absorption spectroscopy to directly measure the temporal evolution of the ionization states of warm dense aluminum. With this, we have achieved for the first time direct measurements of the ionization states of warm dense aluminum using Betatron X-ray radiation probing. Fast Ignition (FI) is an advanced scheme for inertial confinement fusion (ICF), in which the fuel ignition process is decoupled from its compression. Comparing with the conventional central hot-spot scheme for ICF, FI has the advantages of lower ignition threshold and higher gain. The success of FI relies on efficient energy coupling from the heating laser pulse to the hot electrons and subsequent transport of their energy to the compressed fuel. As a secondary part of this thesis, the transport of hot electrons in overdense plasma relevant to FI was studied. In particular, the effect of resistive layers within the target on the hot electron divergence and absorption was investigated. Experimental measurements were carried out and compared to simulations indicating minimal effect on the beam divergence but some attenuation through higher atomic number intermediate layers was observed.
Book Synopsis Impact of Pre-Plasma on Electron Generation and Transport in Laser Plasma Interactions by : Jonathan Lee Peebles
Download or read book Impact of Pre-Plasma on Electron Generation and Transport in Laser Plasma Interactions written by Jonathan Lee Peebles and published by . This book was released on 2017 with total page 248 pages. Available in PDF, EPUB and Kindle. Book excerpt: Relativistic laser plasma interactions in conjunction with an underdense pre-plasma have been shown to generate a two temperature component electron spectrum. The lower temperature component described by "ponderomotive scaling" is relatively well known and understood and is useful for applications such as the fast ignition inertial confinement fusion scheme. The higher energy electrons generated due to pre-plasma are denoted as "super-ponderomotive" electrons and facilitate interesting and useful applications. These include but are not limited to table top particle acceleration and generating high energy protons, x-rays and neutrons from secondary interactions. This dissertation describes experimental and particle-in-cell computational studies of the electron spectra produced from interactions between short pulse high intensity lasers and controlled pre-plasma conditions. Experiments were conducted at 3 laser labs: Texas Petawatt (University of Texas at Austin), Titan (Lawrence Livermore National Laboratory) and OMEGA-EP (University of Rochester). These lasers have different capabilities, and multiple experiments were carried out in order to fully understand super-ponderomotive electron generation and transport in the high intensity laser regime (I > 10^18 W/cm^2). In these experiments, an additional secondary long pulse beam was used to generate different scale lengths of "injected" pre-plasma while the pulse length and intensity of the short pulse beam were varied. The temperature and quantity of super-ponderomotive electrons were monitored with magnetic spectrometers and inferred via bremsstrahlung spectrometers while trajectory was estimated via Cu-K[alpha] imaging. The experimental and simulation data show that super-ponderomotive electrons require pulse lengths of at least 450 fs to be accelerated and that higher intensity interactions generate large magnetic fields which cause severe deflection of the super-ponderomotive electrons. Laser incidence angle is shown to be extremely important in determining hot electron trajectory. Longer pulse length data taken on OMEGA-EP and Titan showed that super-ponderomotive electrons could be created without the need for an initial pre-plasma due to the underdense plasma created during the high intensity interaction alone.
Book Synopsis Atoms, Solids, and Plasmas in Super-Intense Laser Fields by : Dimitri Batani
Download or read book Atoms, Solids, and Plasmas in Super-Intense Laser Fields written by Dimitri Batani and published by Springer Science & Business Media. This book was released on 2001-09-30 with total page 434 pages. Available in PDF, EPUB and Kindle. Book excerpt: Proceedings of the 30th Course of the International School of Quantum Electronics on Atoms, Solids and Plasmas in Super-Intense Laser Fields, held 8-14 July, in Erice, Sicily
Book Synopsis The Interaction of High-Power Lasers with Plasmas by : Shalom Eliezer
Download or read book The Interaction of High-Power Lasers with Plasmas written by Shalom Eliezer and published by CRC Press. This book was released on 2002-08-16 with total page 324 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Interaction of High-Power Lasers with Plasmas provides a thorough self-contained discussion of the physical processes occurring in laser-plasma interactions, including a detailed review of the relevant plasma and laser physics. The book analyzes laser absorption and propagation, electron transport, and the relevant plasma waves in detail. It al
Book Synopsis Laser-Plasma Interactions by : Dino A. Jaroszynski
Download or read book Laser-Plasma Interactions written by Dino A. Jaroszynski and published by CRC Press. This book was released on 2009-03-27 with total page 454 pages. Available in PDF, EPUB and Kindle. Book excerpt: A Solid Compendium of Advanced Diagnostic and Simulation ToolsExploring the most exciting and topical areas in this field, Laser-Plasma Interactions focuses on the interaction of intense laser radiation with plasma. After discussing the basic theory of the interaction of intense electromagnetic radiation fields with matter, the book covers three ap
Book Synopsis Applications of Laser-Plasma Interactions by : Shalom Eliezer
Download or read book Applications of Laser-Plasma Interactions written by Shalom Eliezer and published by CRC Press. This book was released on 2008-12-22 with total page 293 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent advances in the development of lasers with more energy, power, and brightness have opened up new possibilities for exciting applications. Applications of Laser-Plasma Interactions reviews the current status of high power laser applications. The book first explores the science and technology behind the ignition and burn of imploded fusion fue
Book Synopsis Plasmas at High Temperature and Density by : Heinrich Hora
Download or read book Plasmas at High Temperature and Density written by Heinrich Hora and published by Springer Science & Business Media. This book was released on 2008-11-09 with total page 455 pages. Available in PDF, EPUB and Kindle. Book excerpt: "New physics" is an appealing new keyword, not yet devalued by the ravages of inflation. But what has this to do with such an ugly field as plasma physics, steeped in classical physics, mostly outworn, with all its unsolved and ambiguous technological problems and its messy and open ended numerical studies? "New physics" is concerned with quarks, Higgs particles, grand unified theory, super strings, gravitational waves, and the profound basics of cosmology and black holes. It is the field of astonishing quantum effects, demonstrated by the von Klitzing effect and high temperature superconductors. But what can plasma physicists offer, after so many years of expensive and frustrating research to solve the problem of fusion energy? One may suggest that the fascinating research ofchaos with applications to plasma, or the achievements of statistical mechanics applied to plasmas, has something to offer and should be the subject of attention. However, this is not the aim of this book. Complementing the traditional aim of physics, which is to interpret the phenomena of nature by generalizing laws such that exact predictions about new properties and effects can be drawn, this book demonstrates how new physics has been derived over the last 30 years from the state of matter which exists at high temperatures (plasma).
Book Synopsis Super-Intense Laser-Atom Physics IV by : H.G. Muller
Download or read book Super-Intense Laser-Atom Physics IV written by H.G. Muller and published by Springer Science & Business Media. This book was released on 1996-05-31 with total page 630 pages. Available in PDF, EPUB and Kindle. Book excerpt: Atoms in strong radiation fields are interesting objects for study, and the research field that concerns itself with this study is a comparatively young one. For a long period after the ~scovery of the photoelectric effect. it was not possible to generate electro magnetic fields that did more than perturb the atom only slightly, and (first-or~er) perturbation theory could perfectly explain what was going on at those low intensities. The development of the pulsed laser bas changed this state of affairs in a rather dramatic way, and fields can be applied that really have a large, or even dominant influence on atomic structure. In the latter case, w~ speak of super-intense fields. Since the interaction between atoms and electromagnetic waves is characterized by many parameters other than the light intensity, such as frequency, iQnization potential, orbit time, etc., it is actually quite difficult to define what is exactly meant by the term 'super-intense'. Obviously the term does not have an absolute meaning, and intensity should always be viewed in relation to other properties of the system. An atom in a radiation field can thus best be described in terms of various ratios of the quantities involved. The nature of the system sometimes drastically changes if the value of one of these parameters exceeds a certain critical value, and the new regime could be called super-intense with respect to that parameter.
Book Synopsis Experimental Study of Fast Electrons from the Interaction of Ultra Intense Laser and Solid Density Plasmas by : Byoung-ick Cho
Download or read book Experimental Study of Fast Electrons from the Interaction of Ultra Intense Laser and Solid Density Plasmas written by Byoung-ick Cho and published by . This book was released on 2008 with total page 338 pages. Available in PDF, EPUB and Kindle. Book excerpt: A series of experiments have been performed to understand fast electron generation from ultra intense laser-solid interaction, and their transports through a cold material. Using Micro-Electro-Mechanical Systems (MEMS), we contrived various shape of cone and wedge targets. The first set of experiment was for investigating hot electron generations by measuring x-ray production in different energy ranges. K[alpha] and hard x-ray yields were compared when the laser was focused into pyramidal shaped cone targets and wedge shaped targets. Hot electron production is highest in the wedge targets irradiated with transverse polarization, though K[alpha] is maximized with wedge targets and parallel polarization. These results are explained with particle-in-cell (PIC) simulations utilizing PICLS and OOPIC codes. We also investigate hot electron transport in foil, wedge, and cone targets by observing the transition radiation emitted from the targets rear side along with bremsstrahlung x-ray measurement. Twodimensional images and spectra of 800 nm coherent transition radiation (CTR) along with ballistic electron transport analysis have revealed the spatial, temporal, and temperature characteristics of hot electron micro-pulses. Various patterns from different target-laser configurations suggest that hot electrons were guided by the strong static electromagnetic fields at the target boundary. Evidence about fast electron guiding in the cone is also observed. CTR at 400 nm showed that 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 j x B heating, create two populations of electrons at the targets front side and drive them to different directions, with distinct temperatures and temporal characteristics. This interpretation is consistent with the results from 3D-PIC code Virtual Laser Plasma Laboratory (VLPL).
Book Synopsis Hot Electron Diagnostic in a Solid Laser Target by K-Shell Lines Measurement from Ultra-Intense Laser-Plasma Interactions R by :
Download or read book Hot Electron Diagnostic in a Solid Laser Target by K-Shell Lines Measurement from Ultra-Intense Laser-Plasma Interactions R written by and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Characterization of hot electron production (a conversion efficiency from laser energy into electrons) from ultra intense laser-solid target interaction by observing molybdenum (Mo) K[beta] as well as K[alpha] emissions from a buried fluorescence tracer layer in the targets has been done. The experiments used 1.06 [mu]m laser light with an intensity of from 2 x 1018 up to 3 x 102° W cm−2 (20-0.5 ps pulse width) and an on target laser energy of 280-500 J. The conversion efficiency from the laser energy into the energy, carried by hot electrons, has been estimated to be ≈50% for the 0.5 ps shots at an on-target laser intensity of 3 x 102° W cm−2, which increased from ≈30% at 1 x 1019 W cm−2 5 ps shots and ≈ 12% at 2 x 1018 W cm−2 20 ps shots.
