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Adventures in Laser Produced Plasma Research

Description: In the UK the study of laser produced plasmas and their applications began in the universities and evolved to a current system where the research is mainly carried out at the Rutherford Appleton Laboratory Central Laser Facility ( CLF) which is provided to support the universities. My own research work has been closely tied to this evolution and in this review I describe the history with particular reference to my participation in it.
Date: January 13, 2006
Creator: Key, M.
Partner: UNT Libraries Government Documents Department

Status and Prospects of the Fast Ignition Inertial Fusion Concept

Description: Fast ignition is an alternate concept in inertial confinement fusion, which has the potential for easier ignition and greater energy multiplication. If realized it could improve the prospects for inertial fusion energy. It poses stimulating challenges in science and technology and the research is approaching a key stage in which the feasibility of fast ignition will be determined. This review covers the concepts, the state of the science and technology, the near term prospects and the challenges and risks involved in demonstrating high gain fast ignition.
Date: November 15, 2006
Creator: Key, M H
Partner: UNT Libraries Government Documents Department

Fast ignition relevant study of the flux of high intensity laser-generated electrons via a hollow cone into a laser-imploded plasma

Description: An integrated experiment relevant to fast ignition. A Cu-doped deuterated polymer spherical shell target with an inserted hollow Au cone is imploded by a six-beam 900-J, 1-ns laser. A 10-ps, 70-J laser pulse is focused into the cone at the time of peak compression. The flux of high-energy electrons through the imploded material is determined from the yield of Cu K{sub {alpha}} fluorescence by comparison with a Monte Carlo model. The electrons are estimated to carry about 15% of the laser energy. Collisional and Ohmic heating are modeled, and Ohmic effects are shown to be relatively unimportant. An electron spectrometer shows significantly greater reduction of the transmitted electron flux than is calculated in the model. Enhanced scattering by instability-induced magnetic fields is suggested. An extension of this fluor-based technique to measurement of coupling efficiency to the ignition hot spot in future larger-scale fast ignition experiments is outlined.
Date: November 20, 2007
Creator: Key, M
Partner: UNT Libraries Government Documents Department

Edward Teller medal lecture: high intensity lasers and the road to ignition

Description: There has been much progress in the development of high intensity lasers and in the science of laser driven inertially confined fusion such that ignition is now a near term prospect. This lecture reviews the field with particular emphasis on areas of my own involvement.
Date: June 2, 1997
Creator: Key, M. H.
Partner: UNT Libraries Government Documents Department

Configuring NIF for direct drive experiments

Description: The National Ignition Facility (NIF) is a proposed 1.8 MJ laser facility for carrying out experiments in inertial confinement fusion, currently designed for indirect drive experiments. The direct drive approach is being pursued at the 30 kJ Omega facility at the University of Rochester. In this paper we discuss the modifications to the NIF laser that would be required for both indirect and direct drive experiments. A primary concern is the additional cost of adding direct drive capability to the facility.
Date: July 11, 1995
Creator: Eimerl, D.; Rothenberg, J. & Key, M.
Partner: UNT Libraries Government Documents Department

Devloping High Energy Radiography for HED Experiments on NIF and Omega-EP

Description: High energy radiography capabilities are essential for many future DNT/HED experiments on NIF. We have been developing bright, high-energy (15-100 keV), high resolution (< 20 {micro}m), 1-D and 2-D radiography solutions for DNT experiments on NIF. In this LDRD, we have made significant progress utilizing high-energy, high-intensity, short-pulse lasers to generate hard K-{alpha} photons. High energy K-{alpha} sources are created by hot electrons interacting in the target fluor material after irradiation by lasers with intensity I{sub L} > 10{sup 17} W/cm{sup 2}. High resolution point projection 1-D and 2-D radiography have been achieved using {mu}-foil and {mu}-wire targets attached to low-Z substrate materials. The {mu}-wire size was 10 x 10 x 300 {micro}m on a 300 x 300 x 5 {micro}m CH substrate creating the point source size equivalent to these micro targets. This unique technique will utilize the NIF short pulse laser (ARC) as a backlighter suitable for the full range of DNT science experiments on NIF.
Date: February 14, 2008
Creator: Maddox, B; Tommasini, R; Remington, B; Key, M & Town, R
Partner: UNT Libraries Government Documents Department

XUV radiography measurements of direct drive imprint in thin aluminum foils using a Ge x-ray laser on Vulcan

Description: One key aspect for high gain direct drive inertial confinement fusion is the imprint of perturbations in the outer surface of a capsule due to nonuniformities in the direct laser illumination of the capsule. Direct drive implosions are achieved by uniformly irradiating the outside surface of a hollow spherical capsule that contains a layer of fusionable D-T on its inner surface. The intensity of laser irradiation is down with a low intensity ``foot`` at 10{sup 13} W/cm{sup 2} for several nanoseconds before it builds up to more than 10{sup 15} W/cm{sup 2} during the main drive portion of the pulse. Laser ablation of the capsule surface produces a high pressure that accelerates the capsule shell radially inward in a spherical implosion. During this acceleration, perturbations due to surface roughness and due to imprint from spatial nonuniformities in the laser irradiation undergo Rayleigh-Taylor growth, potentially severely degrading performance. Our interest is in studying the imprint process and subsequent Rayleigh-Taylor growth of perturbations in a foil target that is irradiated by a low intensity laser speckle pattern. Previous experiments have been done to study laser imprint with an x-ray laser backlighter at the Nova laser using 0.35 micrometer laser irradiation of a 3 micrometer Si foil. In these experiments we irradiated a 2 micrometer thick Al foil with 0.53 micrometer laser light at 2-8 {times} 10{sup 12} W/cm{sup 2} using the Vulcan laser. We used a Ge x-ray laser as an XUV backlighter to measure the modulation in optical depth of the foil on a CCD during the initial imprint phase and after Rayleigh-Taylor growth with different laser smoothing schemes. 4 refs., 6 figs.
Date: March 29, 1996
Creator: Kalantar, D.H.; Demir, A. & Key, M.H.
Partner: UNT Libraries Government Documents Department

Measurements of direct drive laser imprint in thin foils by XUV radiography using an X-ray laser backlighter

Description: In direct drive inertial confinement fusion, the residual speckle pattern remaining after beam smoothing plays an important role in the seeding of instabilities at the ablation front. We have used an x-ray laser as an XUV backlighter to characterize the imprinted modulation in thin foils for smoothing by random phase plate and spectral dispersion at both 0.35 pm and 0.53 pm irradiation, and induced spatial incoherence at 0.53 pm irradiation. We also demonstrate measurements of the modulation due to a single mode optical imprint generated by a narrow slit interference pattern, and modification of the imprint with a superposed smooth irradiation to study time dependence of the imprinting process. 8 refs., 10 figs.
Date: November 1, 1996
Creator: Kalantar, D.H.; Key, M.H. & DaSilva, L.B.
Partner: UNT Libraries Government Documents Department

Hot electron production and heating by hot electrons in fast ignitor research

Description: In an experimental study of the physics of fast ignition the characteristics of the hot electron source at laser intensities up to 10(to the 20th power) Wcm{sup -2} and the heating produced at depth by hot electrons have been measured. Efficient generation of hot electrons but less than the anticipated heating have been observed.
Date: December 1, 1997
Creator: Key, M.H.; Estabrook, K. & Hammel, B.
Partner: UNT Libraries Government Documents Department

Illumination uniformity requirements for direct drive inertial confinement fusion

Description: The requirements for laser uniformity are discussed in terms of the {ell}-mode spectrum. It is shown that the choice of smoothing methods can significantly alter this spectrum and that this choice should be made in the context of the target physics. Although two dimensional smoothing by spectral dispersion yields a high quality near field beam profile, it results in poor smoothing for low spatial frequency. The partially coherent light method (fiber smoothing) leads to superior smoothing at low spatial frequencies, but has very poor near field beam quality. As a result, it may be desirable to use partially coherent light during the driver pulse foot (at low intensity and when minimizing the laser imprint is critical) and smoothing by spectral dispersion during the main pulse.
Date: July 11, 1995
Creator: Rothenberg, J. E.; Eimerl, D.; Key, M. H. & Weber, S. V.
Partner: UNT Libraries Government Documents Department

Measurement by XUV laser radiography of hydrodynamic perturbations in laser accelerated thin foil targets

Description: A novel diagnostic application of XUV lasers has been developed for the study of the hydrodynamic imprinting of laser speckle pattern on directly driven laser fusion targets. A neon-like Yttrium laser operating at 15.5 nm is used to probe thin foils of Si irradiated with an SSD smoothed laser at 0.35 mm wavelength and 6 10{sup 12} Wcm{sup {minus}2} intensity, simulating the initial phase of irradiation a laser fusion capsule. Measurements of the perturbations in target opacity are made by XUV radiography through the foil. The magnitude and Fourier composition of the perturbations has been determined both before and after Rayleigh Taylor growth showing the mode spectra of both the initial imprint and the subsequent RT growth.
Date: July 11, 1995
Creator: Key, M.H.; Kalantar, D.H. & Barbee, T.W. Jr.
Partner: UNT Libraries Government Documents Department

The scientific benefits of inertially confined fusion research

Description: A striking feature of 25 years of research into inertially confined fusion (ICF) and inertial fusion energy (IFE) has been its significant impact in other fields of science. Most ICF facilities worldwide are now being used in part to support a wider portfolio of research than simply ICF. Reasons for this trend include the high intrinsic interest of the new science coupled with the relative ease and low marginal cost of adapting the facilities particularly lasers, to carry out experiments with goals other than ICF. The availability at ICF laboratories of sophisticated theory and modeling capability and advanced diagnostics has given added impetus. The expertise of ICF specialists has also triggered more lateral scientific spin-offs leading for example to new types of lasers and to related developments in basic science. In a generic sense, the facilities developed for ICF have made possible study of new regimes of the properties of matter at extremely high-energy density and the interaction of ultraintense light with matter. This general opportunity has been exploited in numerous and diverse specific lines of research. Examples elaborated below include laboratory simulation of astrophysical phenomena; studies of the equation of state (EOS) of matter under conditions relevant to the interior of planets and stars; development of uniquely intense sources of extreme ultraviolet (EUV) to hard x-ray emission, notably the x-ray laser; understanding of the physics of strong field interaction of light and matter; and related new phenomena such as laser-induced nuclear processes and high-field-electron accelerators. Some of these developments have potential themselves for further scientific exploitation such as the scientific use of advanced light sources. There are also avenues for commercial exploitation, for example the use of laser plasma sources in EUV lithography. Past scientific progress is summarized here and projections are made for new science that may flow ...
Date: May 14, 1999
Creator: Key, M
Partner: UNT Libraries Government Documents Department

Hot Electron Diagnostic in a Solid Laser Target by Buried K-Shell Fluorer Technique from Ultra-Intense (3x1020W/cm2,< 500 J) Laser-Plasma Interactions on the Petawatt Laser at LLNL

Description: Characterization of hot electron production (a conversion efficiency from laser energy into electrons) in ultra intense laser-solid target interaction, using 1.06 {micro}m laser light with an intensity of up to 3 x 10{sup 20}W cm{sup -2} and an on target laser energy of {le}500 J, has been done by observing K{sub {beta}} as well as K{sub {alpha}} emissions from a buried Mo layer in the targets, which are same structure as in the previous 100 TW experiments but done under less laser intensity and energy conditions ({le} 4 x 10{sup 19} Wcm{sup -2} and {le} 30 J). The conversion efficiency from the laser energy into the energy, carried by hot electrons, has been estimated to be {approx}50%, which are little bit higher than the previous less laser energy ({approx} 20 J) experiments, yet the x-ray emission spectra from the target has change drastically, i.e., gamma flash.
Date: June 29, 2000
Creator: Yasuike, K.; Key, M.H.; Hatchett, S.P. & Snavely, R.A.
Partner: UNT Libraries Government Documents Department

Petawatt Laser Data Analysis and Technology Development

Description: The Petawatt (PW) laser beam line at the LLNL Nova laser facility was unique in the world in supplying an order of magnitude higher power (1PW in pulses of 500 fs duration) than lasers elsewhere. Focused to intensities reaching 3 x l0{sup 20} Wcm{sup -2}, it opened up a new regime of experimental science where free electron energies in the light wave are strongly relativistic. After full operational capability of the PW beam-line was reached, close to 25% of the operation of the Nova facility was dedicated to PW shots for two years, prior to the shut down of Nova in May 1999. A wealth of novel scientific data was obtained and it motivated the primary objective of this June 1 to Oct. 1, 1999 LDRD, which was to complete systematic analysis of the PW laser data. This was done by the team, which had conducted the experiments working with associated experts in theoretical modeling of the complex physical phenomena. A second objective was to develop a key new technology of large area transmission gratings needed for the next step to higher energy PW laser development. This work was done by the team, which developed the reflective grating technology.
Date: September 30, 2000
Creator: Key, M.H. & Perry, M.D.
Partner: UNT Libraries Government Documents Department

Properties and Applications of Laser Generated X-Ray Sources

Description: The rapid development of laser technology and related progress in research using lasers is shifting the boundaries where laser based sources are preferred over other light sources particularly in the XUV and x-ray spectral region. Laser based sources have exceptional capability for short pulse and high brightness and with improvements in high repetition rate pulsed operation, such sources are also becoming more interesting for their average power capability. This study presents an evaluation of the current capabilities and near term future potential of laser based light sources and summarizes, for the purpose of comparison, the characteristics and near term prospects of sources based on synchrotron radiation and free electron lasers. Conclusions are drawn on areas where the development of laser based sources is most promising and competitive in terms of applications potential.
Date: February 25, 2002
Creator: Smith, R F & Key, M H
Partner: UNT Libraries Government Documents Department

X-ray imaging to characterize MeV electronics propagation through plastic targets

Description: A high intensity laser pulse incident on an overdense plasma generates high energy electrons at the critical surface which propagate into the plasma. The details of this propagation is critical to the Fast Ignition process. The energetic electrons emerge as a jet on the far side, but the spread and propagation direction of the jet within the plasma is not well known. By embedding several thin high Z layers in a CH film one can directly image the progress of the electron beam. It loses enough energy to heat the medium through which it travels to hundreds of eV. At that temperature a film, even buried under CH, emits sufficiently hard thermal x-rays to allow imaging the heated area with an x-ray pinhole camera. The film can be thin enough to also see the emissions from another layer near the front of the film. If these two images are visible simultaneously, one can measure the beam spread and propagation direction within the plastic.
Date: September 3, 1999
Creator: Key, M H; Stephens, R B; Koch, J & Pennington, D
Partner: UNT Libraries Government Documents Department

Hot Electron Diagnostic in a Solid Laser Target by K-Shell Lines Measurement from Ultra-Intense Laser-Plasma Interactions R=1.06 (micron)m, 3x10 W/cm -2(less than or equal to) 500 J

Description: 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 {micro}m laser light with an intensity of from 2 x 10{sup 18} up to 3 x 10{sup 20} W cm{sup -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 {approx}50% for the 0.5 ps shots at an on-target laser intensity of 3 x 10{sup 20} W cm{sup -2}, which increased from {approx}30% at 1 x 10{sup 19} W cm{sup -2} 5 ps shots and {approx} 12% at 2 x 10{sup 18} W cm{sup -2} 20 ps shots.
Date: July 27, 2000
Creator: Yasuike, K.; Wharton, K.B.; Key, M.; Hatchett, S. & Snavely, R.
Partner: UNT Libraries Government Documents Department

Developing the Physics Basis of Fast Ignition Experiments at Future Large Fusion-class lasers

Description: The Fast Ignition (FI) concept for Inertial Confinement Fusion (ICF) has the potential to provide a significant advance in the technical attractiveness of Inertial Fusion Energy (IFE) reactors. FI differs from conventional 'central hot spot' (CHS) target ignition by using one driver (laser, heavy ion beam or Z-pinch) to create a dense fuel and a separate ultra-short, ultra-intense laser beam to ignite the dense core. FI targets can burn with {approx} 3X lower density fuel than CHS targets, resulting in (all other things being equal) lower required compression energy, relaxed drive symmetry, relaxed target smoothness tolerances, and, importantly, higher gain. The short, intense ignition pulse that drives this process interacts with extremely high energy density plasmas; the physics that controls this interaction is only now becoming accessible in the lab, and is still not well understood. The attraction of obtaining higher gains in smaller facilities has led to a worldwide explosion of effort in the studies of FI. In particular, two new US facilities to be completed in 2009/2010, OMEGA/OMEGA EP and NIF-ARC (as well as others overseas) will include FI investigations as part of their program. These new facilities will be able to approach FI conditions much more closely than heretofore using direct drive (dd) for OMEGA/OMEGA EP and indirect drive (id) for NIF-ARC. This LDRD has provided the physics basis for the development of the detailed design for integrated Fast ignition experiments on these facilities on the 2010/2011 timescale. A strategic initiative LDRD has now been formed to carry out integrated experiments using NIF ARC beams to heat a full scale FI assembled core by the end of 2010.
Date: February 8, 2008
Creator: Mackinnon, A J; Key, M H; Hatchett, S; MacPhee, A G; Foord, M; Tabak, M et al.
Partner: UNT Libraries Government Documents Department