Magnetic Field Generation and Electron Acceleration in Relativistic Laser Channel PDF Download
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Author: I. Yu Kostyukov
Publisher:
ISBN:
Category : Magnetic fields
Languages : en
Pages : 13
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Book Description
Author: I. Yu Kostyukov
Publisher:
ISBN:
Category : Magnetic fields
Languages : en
Pages : 13
Get Book Here
Book Description
Author: I. Yu Kostyukov
Publisher:
ISBN:
Category : Magnetic fields
Languages : en
Pages : 13
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Book Description
Author: Joshua Joseph May
Publisher:
ISBN:
Category :
Languages : en
Pages : 250
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Book Description
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.
Author: Dimitri Batani
Publisher: Springer Science & Business Media
ISBN: 9780306466151
Category : Science
Languages : en
Pages : 434
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Book Description
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
Author: National Research Council
Publisher: National Academies Press
ISBN: 030908637X
Category : Science
Languages : en
Pages : 177
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Book Description
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.
Author: Tao Wang
Publisher:
ISBN:
Category :
Languages : en
Pages : 176
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Book Description
With the advent of petawatt-class laser facilities, laser intensities reach unprecedented levels enabling novel and efficient regimes of secondary particle and radiation beams. A regime involving relativistic transparency of dense plasmas and the generation of a Megatesla-level azimuthal magnetic field is shown to be promising for generating energetic electrons and collimated gamma-ray beams. This dissertation focuses on the above regime to explore the acceleration mechanism of electrons, to optimize the gamma-ray yield, to examine the application to two-photon pair production, and to investigate the feasibility of magnetic field detection. First, we investigate direct laser acceleration in the presence of a strong azimuthal magnetic field. Test-particle models are built to explain the enhanced acceleration. The magnetic fields mitigate electron dephasing and allow an efficient acceleration over a short distance. We then report the important role of the laser phase velocity on electron confinement in this acceleration regime. We investigate the emission of collimated gamma-ray beams from laser-irradiated channel targets through three-dimensional kinetic simulations. We find a strong power scaling of conversion efficiency into MeV-level photons. The electron-positron pair production via two-photon collisions directly benefits from such a power scaling. We explore two schemes of generating pairs through the linear Breit-Wheeler process: colliding two gamma-ray beams and colliding one gamma-ray beam with blackbody radiation. The strong power scaling boosts the pair yield to the level of 100 000. Our research on the hollow-channel regime corroborates the robustness of prefilled channels. Due to the influence of ion motion, electrons acceleration and photon emission degrade in hollow channels. With a broader angular spread of gamma-ray beams, the pair yield in hollow channels is shown to be less efficient. At last, we examine the feasibility of detecting Megatesla-level magnetic fields. We choose XFEL beams to detect magnetic fields, based on the magnetic field inducing a polarization rotation via the Faraday effect. A setup of structured targets with a prefilled channel which mitigates the reduction of rotation caused by relativistic transparency is necessary to achieve rotations that exceed 0.1 mrad. A study on laser focusing configurations suggests there is flexibility regarding laser intensities.
Author: Dino A. Jaroszynski
Publisher: CRC Press
ISBN: 1584887796
Category : Science
Languages : en
Pages : 454
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Book Description
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
Author: A.M. Prokhorov
Publisher: American Institute of Physics
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 544
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Book Description
Market: For those involved in plasma physics, relativistic beam physics, radiation physics, energy physics, as well as particle accelerators and synchrotron radiation. "An excellent volume which documents the latest thinking and future trends in physics research....The interdisciplinary nature of the material will make this book valuable to both veteran researchers and those new to the field." Physics in Canada Edited by Nobel Prize winner A.M. Prokhorov, these incisive essays review free-electron lasers and microwave generators in plasma physics, relativistic beam physics, radiation physics, and energy physics, as well as particle accelerators and synchrotron radiation.
Author: Liangliang Ji
Publisher: Springer Science & Business Media
ISBN: 3642540074
Category : Science
Languages : en
Pages : 93
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Book Description
This book is dedicated to the relativistic (laser intensity above 1018 W/cm2) laser-plasma interactions, which mainly concerns two important aspects: ion acceleration and extreme-light-field (ELF). Based on the ultra-intense and ultra–short CP lasers, this book proposes a new method that significantly improves the efficiency of heavy-ion acceleration, and deals with the critical thickness issues of light pressure acceleration. More importantly, a series of plasma approaches for producing ELFs, such as the relativistic single-cycle laser pulse, the intense broad-spectrum chirped laser pulse and the ultra-intense isolated attosecond (10-18s) pulse are introduced. This book illustrates that plasma not only affords a tremendous accelerating gradient for ion acceleration but also serves as a novel medium for ELF generation, and hence has the potential of plasma-based optics, which have a great advantage on the light intensity due to the absence of device damage threshold.
Author: Yanzeng Zhang
Publisher:
ISBN:
Category :
Languages : en
Pages : 116
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Book Description
The generation of energetic electron beams in the interaction of an intense laser pulse with plasma is of great interest for many different applications and different mechanisms of electron acceleration have been proposed and studied analytically, numerically, and experimentally over many years. However, due to the multidimensional spatio-temporal characteristics of the electromagnetic (EM) fields and strong nonlinearity of relativistic electron dynamics, the analytic investigations of the mechanism of electron acceleration in the earlier studies are quite limited and thus more profound analysis is needed. This dissertation work is devoted to the analytic investigation of the electron dynamics in the fields of lasers and quasi-static EM fields by employing a novel Hamiltonian, which, by finding proper canonical variables, is time-independent when an appropriately selected perturbation is absent. Such characteristics of the new Hamiltonian can significantly simplify the analysis of electron dynamics. Three different configurations of laser waves and quasi-static EM fields will be considered: counter-propagating laser waves, laser radiation with quasi-static EM fields that can confine the electron motions (e.g., EM fields in the ion channels), and single laser wave but with spatially periodic quasi-static EM fields (e.g., EM fields in electric and magnetic undulators), where the Hamiltonian, canonical variables and choice of perturbations are different for these cases. The mechanism of the electron acceleration will be examined, paying attention to the stochastic acceleration, where the physics underlying the stochastic electron motion is revealed and the maximum electron energies in all cases are obtained.
