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Ultra High Contrast Laser Acceleration Of Relativistic Electrons In Solid Targets
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Book Synopsis Ultra-High-Contrast Laser Acceleration of Relativistic Electrons in Solid Targets by :
Download or read book Ultra-High-Contrast Laser Acceleration of Relativistic Electrons in Solid Targets written by and published by . This book was released on 2013 with total page 181 pages. Available in PDF, EPUB and Kindle. Book excerpt: The cone-guided fast ignition approach to Inertial Con nement Fusion requires laser-accelerated relativistic electrons to deposit kilojoules of energy within an imploded fuel core to initiate fusion burn. One obstacle to coupling electron energy into the core is the ablation of material, known as preplasma, by laser energy proceeding nanoseconds prior to the main pulse. This causes the laser-absorption surface to be pushed back hundreds of microns from the initial target surface; thus increasing the distance that electrons must travel to reach the imploded core. Previous experiments have shown an order of magnitude decrease in coupling into surrogate targets when intentionally increasing the amount of preplasma. Additionally, for electrons to deposit energy within the core, they should have kinetic energies on the order of a few MeV, as less energetic electrons will be stopped prior to the core and more energetic electrons will pass through the core without depositing much energy. Thus a quantitative understanding of the electron energy spectrum and how it responds to varied laser parameters is paramount for fast ignition. For the rst time, this dissertation quantitatively investigates the acceleration of electrons using an ultra-high-contrast laser. Ultra-high-contrast lasers reduce the laser energy that reaches the target prior to the main pulse; drastically reducing the amount of preplasma. Experiments were performed in a cone-wire geometry relevant to fast ignition. These experiments irradiated the inner-tip of a Au cone with the laser and observed electrons that passed through a Cu wire attached to the outer-tip of the cone. The total emission of K x-rays is used as a diagnostic to infer the electron energy coupled into the wire. Imaging the x-ray emission allowed an e ective path-length of electrons within the wire to be determined, which constrained the electron energy spectrum. Experiments were carried out on the ultra-high-contrast Trident laser at Los Alamos National Laboratory and at the low-contrast Titan laser at Lawrence Livermore National Laboratory. The targets were irradiated using these 1.054 [mu]m wavelength lasers at intensities from 1019 to 1020 W/cm2. The coupling of energy into the Cu wire was found to be 2.7x higher when the preplasma was reduced using high-contrast. Additionally, higher laser intensity elongated the e ective path-length of electrons within the wire, indicating that their kinetic energy was higher.
Book Synopsis Ultra-high-contrast Laser Acceleration of Relativistic Electrons in Solid Targets by : Drew Pitney Higginson
Download or read book Ultra-high-contrast Laser Acceleration of Relativistic Electrons in Solid Targets written by Drew Pitney Higginson and published by . This book was released on 2013 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt: The cone-guided fast ignition approach to Inertial Confinement Fusion requires laser-accelerated relativistic electrons to deposit kilojoules of energy within an imploded fuel core to initiate fusion burn. One obstacle to coupling electron energy into the core is the ablation of material, known as preplasma, by laser energy proceeding nanoseconds prior to the main pulse. This causes the laser-absorption surface to be pushed back hundreds of microns from the initial target surface; thus increasing the distance that electrons must travel to reach the imploded core. Previous experiments have shown an order of magnitude decrease in coupling into surrogate targets when intentionally increasing the amount of preplasma. Additionally, for electrons to deposit energy within the core, they should have kinetic energies on the order of a few MeV, as less energetic electrons will be stopped prior to the core and more energetic electrons will pass through the core without depositing much energy. Thus a quantitative understanding of the electron energy spectrum and how it responds to varied laser parameters is paramount for fast ignition. For the first time, this dissertation quantitatively investigates the acceleration of electrons using an ultra-high-contrast laser. Ultra-high-contrast lasers reduce the laser energy that reaches the target prior to the main pulse; drastically reducing the amount of preplasma. Experiments were performed in a cone-wire geometry relevant to fast ignition. These experiments irradiated the inner-tip of a Au cone with the laser and observed electrons that passed through a Cu wire attached to the outer-tip of the cone. The total emission of K[alpha] x-rays is used as a diagnostic to infer the electron energy coupled into the wire. Imaging the x-ray emission allowed an effective path-length of electrons within the wire to be determined, which constrained the electron energy spectrum. Experiments were carried out on the ultra-high-contrast Trident laser at Los Alamos National Laboratory and at the low-contrast Titan laser at Lawrence Livermore National Laboratory. The targets were irradiated using these 1.054 [mu]m wavelength lasers at intensities from 1019 to 1020 W/cm2. The coupling of energy into the Cu wire was found to be 2.7x higher when the preplasma was reduced using high-contrast. Additionally, higher laser intensity elongated the effective path-length of electrons within the wire, indicating that their kinetic energy was higher. To understand the physics behind laser-acceleration of electrons and to examine how this mechanism is affected by the presence of preplasma, simulations were performed to model the laser interaction. This simulations modeled the interaction using a 0.1 to 3 [mu]m exponential preplasma scale length for the high-contrast cases and hydronamically simulated longer scale preplasma (~25 [mu]m) for the low-contrast case. The simulations show that absorption of laser light increases from only 20% with a 0.1 [mu]m scale length to nearly 90% with a long low-contrast-type preplasma. However, as observed in experiments, a smaller fraction of this absorbed energy is transported to the diagnostic wire, which is due to an increased distance that the electrons must travel to reach the wire and increase angular divergence of the electrons. The simulations show that increasing the preplasma scale length from 0.1 to 3 [mu]m increases the average energy by a factor of 2.5x. This is consistent with an increased interaction length over which the electrons can gain energy from the laser. The simulated electrons are compared with experimental data by injecting them into another simulation modeling the transport of electrons through the cone-wire target. This method quantitatively reproduced the experimentally measured the K[alpha] x-ray emission profiles in the high-contrast cases, which gives confidence in the simulations and the generated electron distributions. By showing that the reduction of preplasma increases coupling into surrogate targets this work shows a significant advantage for the fast ignition scheme. Such work gives confidence to facilities that increasing the contrast of their laser systems will increase electron coupling. Additionally, detailed investigation of these high-contrast systems will aid researchers in understanding the effect that preplasma has on the acceleration of electrons.
Book Synopsis New Photon Science and Extreme Field Physics by :
Download or read book New Photon Science and Extreme Field Physics written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The constantly improving capabilities of ultra-high power lasers are enabling interactions of matter with ever extremer fields. As both the on target intensity and the laser contrast are increasing, new physics regimes are becoming accessible and new effects materialize, which in turn enable a host of applications. A first example is the realization of interactions in the transparent-overdense regime (TOR), which is reached by interacting a highly relativistic (a0> 10), ultra high contrast laser pulse with a solid density, nanometer target. Here, a still overdense target is turned transparent to the laser by the relativistic mass increase of the electrons, increasing the skin depth beyond the target thickness and thus enabling volumetric interaction of the laser with the entire target instead of only a small interaction region at the critical density surface. This increases the energy coupling, enabling a range of effects, including relativistic optics and pulse shaping, mono-energetic electron acceleration, highly efficient ion acceleration in the break-out afterburner regime, the generation of relativistic and forward directed surface harmonics. In this talk we will show the theoretical framework for this regime, explored by multi-D, high resolution and high density PIC simulations as well as analytic theory and present measurements and experimental demonstrations of direct relativistic optics, relativistic HHG, electron acceleration, and BOA ion acceleration in the transparent overdense regime. These effects can in turn be used in a host of applications including laser pulse shaping, ICF diagnostics, coherent x-ray sources, and ion sources for fast ignition (IFI), homeland security applications and medical therapy. This host of applications already makes transparent-overdense regime one of general interest, a situation reinforced by the fact that the TOR target undergoes an extremely wide HEDP parameter space during interaction ranging from WDM conditions (e.g . brown dwarfs) early in the interaction to extremely high energy densities of H"011 J/cm3 at peak, dropping back to the underdense but extremely hot parameter range of gamma-ray bursts. Furthermore, whereas today this regime can only be accessed on very few dedicated facilities, employing special targets and pulse cleaning technology, the next generation of laser facilities like RAL-10PW, ELI, or Gekko-Exa will operate in this regime by default, turning its understanding in a necessity rather than a curiosity.
Book Synopsis Relativistic Electron Mirrors by : Daniel Kiefer
Download or read book Relativistic Electron Mirrors written by Daniel Kiefer and published by Springer. This book was released on 2014-07-25 with total page 127 pages. Available in PDF, EPUB and Kindle. Book excerpt: A dense sheet of electrons accelerated to close to the speed of light can act as a tuneable mirror that can generate bright bursts of laser-like radiation in the short wavelength range simply via the reflection of a counter-propagating laser pulse. This thesis investigates the generation of such a relativistic electron mirror structure in a series of experiments accompanied by computer simulations. It is shown that such relativistic mirror can indeed be created from the interaction of a high-intensity laser pulse with a nanometer-scale, ultrathin foil. The reported work gives a intriguing insight into the complex dynamics of high-intensity laser-nanofoil interactions and constitutes a major step towards the development of a relativistic mirror, which could potentially generate bright burst of X-rays on a micro-scale.
Book Synopsis Laser Physics at Relativistic Intensities by : A.V. Borovsky
Download or read book Laser Physics at Relativistic Intensities written by A.V. Borovsky and published by Springer. This book was released on 2010-12-01 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: For the first time in a book, this monograph describes relativistic and charge-displacement self-channelling, which is the major finding in the physics of superintense laser beams. It also presents general nonlinear models of lasers - plasma interactions specifically in the case of extremely high intensities.
Book Synopsis Progress in Ultrafast Intense Laser Science by : Antonio Giulietti
Download or read book Progress in Ultrafast Intense Laser Science written by Antonio Giulietti and published by Springer Science & Business Media. This book was released on 2010-05-21 with total page 223 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume covers a range of topics from this interdisciplinary field, focusing on coherent responses of gaseous and condensed matter to ultrashort intense laser pulses, propagation of intense laser pulses, and laser-plasma interaction and its applications.
Book Synopsis Coherence and Ultrashort Pulse Laser Emission by : F. J. Duarte
Download or read book Coherence and Ultrashort Pulse Laser Emission written by F. J. Duarte and published by BoD – Books on Demand. This book was released on 2010-12-30 with total page 702 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this volume, recent contributions on coherence provide a useful perspective on the diversity of various coherent sources of emission and coherent related phenomena of current interest. These papers provide a preamble for a larger collection of contributions on ultrashort pulse laser generation and ultrashort pulse laser phenomena. Papers on ultrashort pulse phenomena include works on few cycle pulses, high-power generation, propagation in various media, to various applications of current interest. Undoubtedly, Coherence and Ultrashort Pulse Emission offers a rich and practical perspective on this rapidly evolving field.
Book Synopsis Theoretical Study of Ultra High Intensity Laser-produced High-current Relativistic Electron Beam Transport Through Solid Targets by : Arnaud Debayle
Download or read book Theoretical Study of Ultra High Intensity Laser-produced High-current Relativistic Electron Beam Transport Through Solid Targets written by Arnaud Debayle and published by . This book was released on 2008 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This PhD thesis is a theoretical study of high-current relativistic electron beam transport through solid targets. In the ?rst part, we present an interpretation of a part of experimental results of laser- produced electron beam transport in aluminium foil targets. We have estimated the fast electron beam characteristics and we demonstrated that the collective e?ects dominate the transport in the ?rst tens of μm of propagation. These quantitative estimates were done with the transport models already existing at the beginning of this thesis. These models are no longer su?cient in the case a fast electron beam propagation in insulator targets. Thus, in the second part, we have developed a propagation model of the beam that includes the e?ects of electric ?eld ionization and the collisional ionization by the plasma electrons. We present estimates of the electron energy loss induced by the target ionization, and we discuss its dependence on the beam and target parameters. In the case of a relatively low fast electron density, we demonstrated that the beam creates a plasma where the electons are not in a local thermodynamic equilibrium with ions. We have examined the beam stability and we demonstrated that transverse instabilities can be excited by the relativistic electron beam over the propagation distances of 30 - 300 μm depending on the perturbation wavelength.
Book Synopsis Ultlra-intense Laser-matter Interactions at Extreme Parameters by :
Download or read book Ultlra-intense Laser-matter Interactions at Extreme Parameters written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The field of shortpulse lasers has seen rapid growth in the recent years with the three major boundaries of energy, pulse duration and repetition rate being pushed in ever extremer regions. At peak powers, already exceeding 1022 W/cm2, in virtually every experiment in relativistic laser physics, the laser pulse interacts with a more or less extended and heated plasma, due to prepulses and ASE-like pedestals on ps - ns time scales. By developing a new technique for ultrahigh contrast, we were able to initiate the next paradigm shift in relativistic laser-matter interactions, allowing us to interact ultrarelativistic pulses volumetrically with overdense targets. This becomes possible by using target and laser parameters that will turn the target relativistically transparent during the few 10s-100s femtoseconds fo the interaction. Specifically, we interact an ultraintese, ultrahigh contrast pulse with solid density, free standing, nanometer diamond target. This paradigm change towards a volumetric overdense interaction in turn enables new particle acceleration mechanisms for both electrons and ions, as well as forward directed relativistic surface harmonics. We report here on first experiments done on those topics at the 200 TW Trident laser at Los Alamos as well as at the Ti:Sapphire system at MBI. We will compare the experimental data to massive large scale 3D simulations done on the prototype of LANL's new Petafiop supercomputer Roadrunner, which is leading the current top 500 list. Specifically, we developed a shortpulse OPA based pulse cleaning technique. Fielding it at the Trident 200 TW laser at Los Alamos, we were able to improve the pulse contrast by 6 orders of magnitude to better than 2 x 10−12 at less than a ps. This enabled for the first time the interaction of a 100J, 200TW laser pulse with a truly solid target with virtually no expansion before the main pulse - target interaction, making possible the use of very thin targets, The thinnest of these at less than 3nm, i.e. 1/300 of the laser wavelength, are even thinner than the plasma skin depth. This drastically changes the laser-matter interaction physics leading to the emergence of new particle acceleration mechanisms, like Break-Out Afterburner (BOA) Acceleration, driven by a relativistic, kinetic plasma instability or Radiation Pressure Acceleration (RPA), driven by stabilized charge separation. Furthermore, these interactions also produce relativistic high harmonics in forward direction as well as mono-en, ergetic electron pulses which might lend itself as a source for fully coherent Thomson scattering in the mulit-keV regime. In this talk I will present an overview over the laser developments leading to this paradigm change as well as over the theoretical and experimental results following from it. Specifically we were able for the first time to demonstrate BOA acceleration of Carbon ions to up to 0.5 GeV using a laser pulse with H"02° W/cm2 intensity and showing the scalability of this mechanism into regimes relevant for Hadron Therapy. We were further able to demonstrate mono-energetic electron break-out from ultrathin targets, as a first step towards a flying mirror.
Book Synopsis Relativistic Electron Beam Interaction and Ka - Generation in Solid Targets by :
Download or read book Relativistic Electron Beam Interaction and Ka - Generation in Solid Targets written by and published by . This book was released on 1999 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: When fs laser pulses interact with solid surfaces at intensities I?2> 1018 W/cm2?m2, collimated relativistic electron beams are generated. These electrons can be used for producing intense X-radiation (bremsstrahlung or K{sub {alpha}}) for pumping an innershell X-ray laser. The basic concept of such a laser involves the propagation of the electron beam in a material which converts electron energy into appropriate pump photons. Using the ATLAS titanium-sapphire laser at Max-Planck-Institut fuer Quantenoptik, the authors investigate the generation of hot electrons and of characteristic radiation in copper. The laser (200 mJ/130 fs) is focused by means of an off-axis parabola to a diameter of about 10?m. By varying the position of the focus, they measure the copper K{sub {alpha}} - yield as a function of intensity in a range of 1015 to 2 x 1018 W/cm2 while keeping the laser pulse energy constant. Surprisingly, the highest emission is obtained at an intensity of about 1017 W/cm2. However, this result is readily explained by the weak scaling of the hot-electron temperature with intensity. An efficiency of 2 x 10−4 for the conversion of laser energy into copper K{sub {alpha}} is measured. Simulations of the interaction of the hot electrons with the cold target material and the conversion into X-rays are carried out by means of the TIGER/ITS code, a time-independent, coupled electron/photon Monte Carlo transport code. The code calculates the propagation of individual electrons and the generation of photons in cold material. Comparison of the code predictions with the data shows an efficiency of 15% for the generation of electrons with energies in the 100 keV range. A second experiment involves the demonstration of photopumping of an innershell transition in cobalt by the copper radiation. Comparing the emission with the one of nickel, which is not photopumped by copper K{sub {alpha}} photons, an enhancement of more than a factor of two was obtained. An essential part of this experiment is the use of a 1 mm carbon sheet to block the electrons from the material to be photopumped.
Book Synopsis Laser Ion Acceleration from the Interaction of Ultra-Intense Laser Pulse with Thi Foils by :
Download or read book Laser Ion Acceleration from the Interaction of Ultra-Intense Laser Pulse with Thi Foils written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The discovery that ultra-intense laser pulses (I> 10[sup 18] W/cm[sup 2]) can produce short pulse, high energy proton beams has renewed interest in the fundamental mechanisms that govern particle acceleration from laser-solid interactions. Experiments have shown that protons present as hydrocarbon contaminants on laser targets can be accelerated up to energies> 50 MeV. Different theoretical models that explain the observed results have been proposed. One model describes a front-surface acceleration mechanism based on the ponderomotive potential of the laser pulse. At high intensities (I> 10[sup 18] W/cm[sup 2]), the quiver energy of an electron oscillating in the electric field of the laser pulse exceeds the electron rest mass, requiring the consideration of relativistic effects. The relativistically correct ponderomotive potential is given by U[sub p] = ([1 + I[lambda][sup 2]/1.3 x 10[sup 18]][sup 1/2] - 1) m[sub o]c[sup 2], where I[lambda][sup 2] is the irradiance in W[micro]m[sup 2]/cm[sup 2] and m[sub o]c[sup 2] is the electron rest mass. At laser irradiance of I[lambda][sup 2] [approx] 10[sup 20] W[micro]m[sup 2]/cm[sup 2], the ponderomotive potential can be of order several MeV. A few recent experiments--discussed in Chapter 3 of this thesis--consider this ponderomotive potential sufficiently strong to accelerate protons from the front surface of the target to energies up to tens of MeV. Another model, known as Target Normal Sheath Acceleration (TNSA), describes the mechanism as an electrostatic sheath on the back surface of the laser target. According to the TNSA model, relativistic hot electrons created at the laser-solid interaction penetrate the foil where a few escape to infinity. The remaining hot electrons are retained by the target potential and establish an electrostatic sheath on the back surface of the target.
Book Synopsis High Field Plasmonics by : Luca Fedeli
Download or read book High Field Plasmonics written by Luca Fedeli and published by Springer. This book was released on 2016-09-26 with total page 194 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis describes pioneering research on the extension of plasmonics schemes to the regime of high-intensity lasers. By presenting a rich and balanced mix of experimentation, theory and simulation, it provides a comprehensive overview of the emerging field of high field plasmonics, including open issues and perspectives for future research. Combining specially designed targets and innovative materials with ultrashort, high-contrast laser pulses, the author experimentally demonstrates the effects of plasmon excitation on electron and ion emission. Lastly, the work investigates possible further developments with the help of numerical simulations, revealing the potential of plasmonics effects in the relativistic regime for advances in laser-driven sources of radiation, and for the manipulation of extreme light at the sub-micron scale.
Book Synopsis Ion Acceleration from the Interaction of Ultra-Intense Lasers with Solid Foils by :
Download or read book Ion Acceleration from the Interaction of Ultra-Intense Lasers with Solid Foils written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The discovery that ultra-intense laser pulses (I> 10[sup 18] W/cm[sup 2]) can produce short pulse, high energy proton beams has renewed interest in the fundamental mechanisms that govern particle acceleration from laser-solid interactions. Experiments have shown that protons present as hydrocarbon contaminants on laser targets can be accelerated up to energies> 50 MeV. Different theoretical models that explain the observed results have been proposed. One model describes a front-surface acceleration mechanism based on the ponderomotive potential of the laser pulse. At high intensities (I> 10[sup 18] W/cm[sup 2]), the quiver energy of an electron oscillating in the electric field of the laser pulse exceeds the electron rest mass, requiring the consideration of relativistic effects. The relativistically correct ponderomotive potential is given by U[sub p] = ([1 + I[lambda][sup 2]/1.3 x 10[sup 18]][sup 1/2] - 1) m[sub o]c[sup 2], where I[lambda][sup 2] is the irradiance in W [micro]m[sup 2]/cm[sup 2] and m[sub o]c[sup 2] is the electron rest mass. At laser irradiance of I[lambda][sup 2] [approx] 10[sup 20] W [micro]m[sup 2]/cm[sup 2], the ponderomotive potential can be of order several MeV. A few recent experiments--discussed in Chapter 3 of this thesis--consider this ponderomotive potential sufficiently strong to accelerate protons from the front surface of the target to energies up to tens of MeV. Another model, known as Target Normal Sheath Acceleration (TNSA), describes the mechanism as an electrostatic sheath on the back surface of the laser target. According to the TNSA model, relativistic hot electrons created at the laser-solid interaction penetrate the foil where a few escape to infinity. The remaining hot electrons are retained by the target potential and establish an electrostatic sheath on the back surface of the target. In this thesis we present several experiments that study the accelerated ions by affecting the contamination layer from which they originate. Radiative heating was employed as a method of removing contamination from palladium targets doped with deuterium. We present evidence that ions heavier than protons can be accelerated if hydrogenous contaminants that cover the laser target can be removed. We show that deuterons can be accelerated from the deuterated-palladium target, which has been radiatively heated to remove contaminants. Impinging a deuteron beam onto a tritiated-titanium catcher could lead to the development of a table-top source of short-pulse, 14-MeV fusion neutrons. We also show that by using an argon-ion sputter gun, contaminants from one side of the laser target can be selectively removed without affecting the other side. We show that irradiating a thin metallic foil with an ultra-intense laser pulse produces a proton beam with a yield of 1.5-2.5 10[sup 11] and temperature, kT = 1.5 MeV with a maximum proton energy> 9 MeV. Removing contaminants from the front surface of the laser target with an argon-ion sputter gun, had no observable effect on the proton beam. However, removing contaminants from the back surface of the laser target reduced the proton beam by two orders of magnitude to, at most, a yield of [approx] 10[sup 9] and a maximum proton energy 4 MeV. Based on these observations, we conclude that the majority ( 99%) of high energy protons (E> 5 MeV) from the interaction of an ultra-intense laser pulse with a thin foil originate on the back surface of the foil--as predicted by the TNSA model. Our experimental results are in agreement with PIC simulations showing back surface protons reach energies up to 13 MeV, while front surface protons reach a maximum energy of 4 MeV. Well diagnosed and controllable proton beams will have many applications: neutron radiography, material damage studies, production of medical isotopes, and as a high-resolution radiography tool for diagnosing opaque materials and plasmas. Well collimated and focusable ion beams may also prove beneficial for alternative inertial-fusion concepts such as proton fast ignition, a potentially viable method for achieving a controlled fusion reaction in the laboratory earlier than expected.
Download or read book Laser Pulses written by Igor Peshko and published by BoD – Books on Demand. This book was released on 2012-10-17 with total page 562 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book discusses aspects of laser pulses generation, characterization, and practical applications. Some new achievements in theory, experiments, and design are demonstrated. The introductive chapter shortly overviews the physical principles of pulsed lasers operation with pulse durations from seconds to yoctoseconds. A theory of mode-locking, based on the optical noise concept, is discussed. With this approximation, all paradoxes of ultrashort laser pulse formation have been explained. The book includes examples of very delicate laser operation in biomedical areas and extremely high power systems used for material processing and water purification. We hope this book will be useful for engineers and managers, for professors and students, and for those who are interested in laser science and technologies.
Book Synopsis Applications of Laser-Driven Particle Acceleration by : Paul Bolton
Download or read book Applications of Laser-Driven Particle Acceleration written by Paul Bolton and published by CRC Press. This book was released on 2018-06-04 with total page 552 pages. Available in PDF, EPUB and Kindle. Book excerpt: The first book of its kind to highlight the unique capabilities of laser-driven acceleration and its diverse potential, Applications of Laser-Driven Particle Acceleration presents the basic understanding of acceleration concepts and envisioned prospects for selected applications. As the main focus, this new book explores exciting and diverse application possibilities, with emphasis on those uniquely enabled by the laser driver that can also be meaningful and realistic for potential users. It also emphasises distinction, in the accelerator context, between laser-driven accelerated particle sources and the integrated laser-driven particle accelerator system (all-optical and hybrid versions). A key aim of the book is to inform multiple, interdisciplinary research communities of the new possibilities available and to inspire them to engage with laser-driven acceleration, further motivating and advancing this developing field. Material is presented in a thorough yet accessible manner, making it a valuable reference text for general scientific and engineering researchers who are not necessarily subject matter experts. Applications of Laser-Driven Particle Acceleration is edited by Professors Paul R. Bolton, Katia Parodi, and Jörg Schreiber from the Department of Medical Physics at the Ludwig-Maximilians-Universität München in München, Germany. Features: Reviews the current understanding and state-of-the-art capabilities of laser-driven particle acceleration and associated energetic photon and neutron generation Presents the intrinsically unique features of laser-driven acceleration and particle bunch yields Edited by internationally renowned researchers, with chapter contributions from global experts
Book Synopsis Particle-in-cell Simulations of the Acceleration of Electrons from the Interaction of a Relativistic Laser Reflecting from Solid Density Targets by : Gregory K. Ngirmang
Download or read book Particle-in-cell Simulations of the Acceleration of Electrons from the Interaction of a Relativistic Laser Reflecting from Solid Density Targets written by Gregory K. Ngirmang and published by . This book was released on 2018 with total page 101 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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.
