Author: Graeme Gordon Scott
Publisher:
ISBN:
Category :
Languages : en
Pages : 342
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Compact laser driven ion sources have inspired cautious optimism that they may provide an alternative to conventional accelerators for existing applications, such as in medicine, or aid the realisation of new ones such as fusion energy. However, the sources must be developed, with increased conversion efficiency of laser to proton energy being high on the list of requirements. Recent reports in the literature have shown that record conversion efficiencies can be achieved with double pulse interactions, and this thesis proceeds with this theme. The double pulse operation of the plasma mirror is characterised for the first time, in terms of the post interaction far field quality, and integrated reflectivity. The main pulse reflectivity is significantly enhanced to 96% and the far field remains of high optical quality up to five picoseconds after the prepulse interaction, within the regime for conversion efficiency enhancement. These observations are explained by perturbations of the quasi-near field intensity distribution seeding nonuniformities in the plasma expansion of the plasma mirror surface. A novel plasma half cavity target geometry is investigated which utilises the high fraction of laser energy reflected from an ionised surface and refocuses it such that a double pulse interaction is attained. This new geometry is found to double the laser to proton energy conversion efficiency, compared with planar foil interactions and to modify the low energy region of the proton spectrum. For pulse separations of tens of picoseconds, a long time delay regime is identified for planar foil interactions, where a significant reduction in maximum proton energy and conversion efficiency is reversed, and return to that expected for single pulse interactions. This is explained by the main pulse interacting with bulk target expansion induced by the prepulse. Increased electron temperatures from enhanced absorption in the preplasma are found to mitigate the detrimental effects on ion acceleration, associated with rear surface density scale lengths.
Author: Christopher R. Willis
Publisher:
ISBN:
Category :
Languages : en
Pages : 206
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Book Description
Over the past two decades, a number of experiments have been performed demonstrating the acceleration of ions from the interaction of an intense laser pulse with a thin, solid density target. These ions are accelerated by quasi-static electric fields generated by energetic electrons produced at the front of the target, resulting in ion energies up to tens of MeV. These ions have been widely studied for a variety of potential applications ranging from treatment of cancer to the production of neutrons for advanced radiography techniques. However, realization of these applications will require further optimization of the maximum energy, spectrum, or species of the accelerated ions, which has been a primary focus of research to date. This thesis presents two experiments designed to optimize several characteristics of the accelerated ion beam. The first of these experiments took place on the GHOST laser system at the University of Texas at Austin, and was designed to demonstrate reliable acceleration of deuterium ions, as needed for the most efficient methods of neutron generation from accelerated ions. This experiment leveraged cryogenically cooled targets coated in D2O ice to suppress the protons which typically dominate the accelerated ions, producing as many as 2 x 10^10 deuterium ions per 1 J laser shot, exceeding the proton yield by an average ratio of 5:1. The second major experiment in this work was performed on the Scarlet laser system at The Ohio State University, and studied the accelerated ion energy, yield, and spatial distribution as a function of the target thickness. In principle, the peak energy increases with decreasing target thickness, with the thinnest targets accessing additional acceleration mechanisms which provide favorable scaling with the laser intensity. However, laser prepulse characteristics provide a lower bound for the target thickness, yielding an optimum target thickness for ion acceleration which is dependent on the laser system. This experiment utilized new liquid crystal film targets developed at OSU, which may be formed at variable thicknesses from tens of nanometers to several microns. On this experiment, an optimum ion energy and flux was reached for targets of 600-900 nm, providing a peak proton energy of 24 MeV, and total ion flux of >10^9 protons over 3.4 MeV from 5.5 J of laser energy at an intensity of 1 x 10^20 W/cm^2. The primary ion diagnostics for these two experiments are described in detail, including the analysis techniques needed to extract absolutely calibrated spatial and spectral distributions of the accelerated ions. Additionally, a new technique for target alignment is presented, providing repeatable target alignment on the micron scale. This allows for a repeatable laser intensity on target, allowing improved shot to shot consistency on high intensity experiments. In addition to these two experiments, work on the upgrade and characterization of the 400 TW Scarlet laser is discussed, including several calculations critical to the design and upgrade of the laser system, as well as prepulse characterization needed for experiments on thin targets.
Author: Fernando Ferroni
Publisher: IOS Press
ISBN: 1614991286
Category : Science
Languages : en
Pages : 286
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Book Description
Impressive progress has been made in the field of laser-plasma acceleration in the last decade, with outstanding achievements from both experimental and theoretical viewpoints. Closely exploiting the development of ultra-intense, ultrashort pulse lasers, laser-plasma acceleration has developed rapidly, achieving accelerating gradients of the order of tens of GeV/m, and making the prospect of miniature accelerators a more realistic possibility.This book presents the lectures delivered at the Enrico Fermi International School of Physics and summer school: 'Laser-Plasma Acceleration', held in Varenna, Italy, in June 2011.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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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.
Author: Teh Lin
Publisher:
ISBN:
Category :
Languages : en
Pages : 238
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Author: Jörg Schreiber
Publisher:
ISBN:
Category :
Languages : de
Pages : 82
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Author: Kaoru Yamanouchi
Publisher: Springer Science & Business Media
ISBN: 3642183271
Category : Science
Languages : en
Pages : 257
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Book Description
The PUILS series delivers up-to-date reviews of progress in Ultrafast Intense Laser Science, a newly emerging interdisciplinary research field spanning atomic and molecular physics, molecular science, and optical science, which has been stimulated by the recent developments in ultrafast laser technologies. Each volume compiles peer-reviewed chapters authored by researchers at the forefront of each their own subfields of UILS. Every chapter begins with an overview of the topics to be discussed, so that researchers unfamiliar to the subfield, as well as graduate students, can grasp the importance and attractions of the research topic at hand; these are followed by reports of cutting-edge discoveries. This seventh volume covers a broad range of topics from this interdisciplinary research field, focusing on the ionization of atoms and molecules, ultrafast responses of protons and electrons within a molecule, molecular alignment, high-order harmonics and attosecond pulse generation, and acceleration of electrons and ions in laser plasmas.
Author: Luca Fedeli
Publisher: Springer
ISBN: 3319442902
Category : Science
Languages : en
Pages : 194
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Book Description
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.
Author: Igor Peshko
Publisher: BoD – Books on Demand
ISBN: 9535107968
Category : Technology & Engineering
Languages : en
Pages : 562
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Book Description
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.
Author: Emmanuel d'Humières
Publisher:
ISBN: 9789535107965
Category :
Languages : en
Pages :
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