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A Bremsstrahlung Spectrometer using k-edge and Differential Filters with Image plate dosimeters

Description: A Bremsstrahlung spectrometer using k-edge and differential filtering has been used with Image Plate dosimeters to measure the x-ray fluence from short-pulse laser/target interactions. An electron spectrometer in front of the Bremsstrahlung spectrometer deflects electrons from the x-ray line of sight and simultaneously measures the electron spectrum. The response functions were modeled with the Monte Carlo code Integrated Tiger Series 3.0 and the dosimeters calibrated with radioactive sources. Electron distributions with slope temperatures in the MeV range are inferred from the Bremsstrahlung spectra.
Date: May 2, 2008
Creator: Chen, C; Mackinnon, A; Beg, F; Chen, H; Key, M; King, J A et al.
Partner: UNT Libraries Government Documents Department

Electron-Heated Target Temperature Measurements in Petawatt Laser Experiments Based on Extreme Ultraviolet Imaging and Spectroscopy

Description: Three independent methods (XUV spectroscopy, imaging at 68 eV and 256 eV) have been used to measure planar target rear surface plasma temperature due to heating by hot electrons. The hot electrons are produced by ultra-intense laser plasma interactions using the 150 J, 0.5 ps Titan laser. Soft x-ray spectroscopy in the 50-400 eV region and imaging at the 68 eV and 256 eV photon energies were used to determine the rear surface temperature of planar CD targets. Temperatures were found to be in the 60-150 eV range, with good agreement between the three diagnostics.
Date: May 2, 2008
Creator: Ma, T; Beg, F; Macphee, A; Chung, H; Key, M; Mackinnon, A et al.
Partner: UNT Libraries Government Documents Department

Epithermal Neutron Source for Neutron Resonance Spectroscopy (NRS) using High Intensity, Short Pulse Lasers

Description: A neutron source for neutron resonance spectroscopy (NRS) has been developed using high intensity, short pulse lasers. This measurement technique will allow for robust measurements of interior ion temperature of laser-shocked materials and provide insight into equation of state (EOS) measurements. The neutron generation technique uses protons accelerated by lasers off of Cu foils to create neutrons in LiF, through (p,n) reactions with {sup 7}Li and {sup 19}F. The distribution of the incident proton beam has been diagnosed using radiochromic film (RCF). This distribution is used as the input for a (p,n) neturon prediction code which is compared to experimentally measured neutron yields. From this calculation, a total fluence of 1.8 x 10{sup 9} neutrons is infered, which is shown to be a reasonable amount for NRS temperature measurement.
Date: April 22, 2010
Creator: Higginson, D P; McNaney, J M; Swift, D C; Bartal, T; Hey, D S; Pape, S L et al.
Partner: UNT Libraries Government Documents Department

Hot dense matter creation in short-pulse laser interaction with tamped foils

Description: The possibility of producing hot dense matter has important applications for the understanding of transport processes in inertial confinement fusion (ICF) [1] and laboratory astrophysics experiments [2]. While the success of ICF requires the correct solution of a complex interaction between laser coupling, equation-of-state, and particle transport problems, the possibility of experimentally recreating conditions found during the ignition phase in a simplified geometry is extremely appealing. In this paper we will show that hot dense plasma conditions found during ICF ignition experiments can be reproduced by illuminating a tamped foil with a high intensity laser. We will show that temperatures on the order of kiloelectronvolts at solid densities can be achieved under controlled conditions during the experiment. Hydrodynamic tamping by surface coatings allows to reach higher density regimes by enabling the diagnosis of matter that has not yet begun to decompress, thus opening the possibility of directly investigating strongly coupled systems [3]. Our experimental diagnostics is based on K-shell spectroscopy coupled to x-ray imaging techniques. Such techniques have recently become prevalent in the diagnosis of hot dense matter [4]. By looking at the presence, and relative strengths, of lines associated with different ionization states, spectroscopy provides considerable insight into plasma conditions. At the same time, curved crystal imaging techniques allow for the spatial resolution of different regions of the target, both allowing for comparison of heating processes with the results of Particle-In-Cell (PIC) and hybrid simulation codes.
Date: August 15, 2006
Creator: Chen, S; Pasley, J; Beg, F; Gregori, G; Evans, R G; Notley, M et al.
Partner: UNT Libraries Government Documents Department

Extreme Ultraviolet Imaging of Electron Heated Targets in Petawatt Laser Experiments

Description: The study of the transport of electrons, and the flow of energy into a solid target or dense plasma, is instrumental in the development of fast ignition inertial confinement fusion. An extreme ultraviolet (XUV) imaging diagnostic at 256 eV and 68 eV provides information about heating and energy deposition within petawatt laser-irradiated targets. XUV images of several irradiated solid targets are presented.
Date: November 29, 2007
Creator: Ma, T; MacPhee, A; Key, M; Akli, K; Mackinnon, A; Chen, C et al.
Partner: UNT Libraries Government Documents Department

Radiative Properties of High Wire Number Tungsten Arrays with Implosion Times up to 250 ns

Description: High wire number, 25-mm diameter tungsten wire arrays have been imploded on the 8-MA Saturn generator, operating in a long-pulse mode. By varying the mass load from 710 to 6140 ps/cm, implosion times of 130 to 250 ns have been obtained with implosion velocities of 50 to 25 cn-dys, respectively. These z-pinch implosions produced plasmas with millimeter diameters that radiated 600 to 800 kJ of x-rays, with powers of 20 to 49 TW; the corresponding pulse widths were 19 to 7.5 ns, with risetimes ranging from 6.5 to 4.0 ns. These powers and pulse widths are similar to those achieved with 50 ns implosion times on Saturn. Two-dimensional, radiation- magnetohydrodynamic calculations indicate that the imploding shells in these long implosion time experiments are comparable in width to those in the short pulse cases. This can only be due to lower initial perturbations. A heuristic wire array model suggests that the reduced perturbations, in the long pulse cases, may be due to the individual wire merger occurring well before the acceleration of the shell. The experiments and modeling suggest that 150 to 200 ns implosion time z-pinches could be employed for high-power, x-ray source applications.
Date: February 2, 1999
Creator: Beg, F.N.; Coverdale, C.A.; Deeney, C.; Douglas, M.R.; Haines, M.G.; Peterson, D.L. et al.
Partner: UNT Libraries Government Documents Department

Diagnostics for Fast Ignition Science

Description: The concept for Electron Fast Ignition Inertial Confinement Fusion demands sufficient laser energy be transferred from the ignitor pulse to the assembled fuel core via {approx}MeV electrons. We have assembled a suite of diagnostics to characterize such transfer. Recent experiments have simultaneously fielded absolutely calibrated extreme ultraviolet multilayer imagers at 68 and 256eV; spherically bent crystal imagers at 4 and 8keV; multi-keV crystal spectrometers; MeV x-ray bremmstrahlung and electron and proton spectrometers (along the same line of sight); nuclear activation samples and a picosecond optical probe based interferometer. These diagnostics allow careful measurement of energy transport and deposition during and following laser-plasma interactions at extremely high intensities in both planar and conical targets. Augmented with accurate on-shot laser focal spot and pre-pulse characterization, these measurements are yielding new insight into energy coupling and are providing critical data for validating numerical PIC and hybrid PIC simulation codes in an area that is crucial for many applications, particularly fast ignition. Novel aspects of these diagnostics and how they are combined to extract quantitative data on ultra high intensity laser plasma interactions are discussed, together with implications for full-scale fast ignition experiments.
Date: May 6, 2008
Creator: MacPhee, A; Akli, K; Beg, F; Chen, C; Chen, H; Clarke, R et al.
Partner: UNT Libraries Government Documents Department

Fast Electron Generation in Cones with Ultra-Intense Laser Pulses

Description: Experimental results from copper cones irradiated with ultra-intense laser light are presented. Spatial images and total yields of Cu K{sub {alpha}} fluorescence were measured as a function of the laser focusing properties. The fluorescence emission extends into the cone approximately 300 {micro}m from the cone tip and cannot be explained by ray tracing including cone wall absorption. In addition the total fluorescence yield from cones is an order of magnitude higher than for equivalent mass foil targets. Indications are that the physics of the laser cone interaction is dominated by preplasma created from the long duration, low energy pre-pulse from the laser.
Date: December 7, 2007
Creator: Mackinnon, A; VanWoerkom, L; Akli, K; Bartal, T; Beg, F; Chawla, S et al.
Partner: UNT Libraries Government Documents Department

Laser heating of solid matter by light pressure-driven shocks

Description: Heating by irradiation of a solid surface in vacuum with 5 x 10{sup 20} W cm{sup -2}, 0.8 ps, 1.05 {micro}m wavelength laser light is studied by x-ray spectroscopy of the K-shell emission from thin layers of Ni, Mo and V. A surface layer is heated to {approx} 5 keV with an axial temperature gradient of 0.6 {micro}m scale length. Images of Ni Ly{sub {alpha}} show the hot region has a {approx} 25 {micro}m diameter, much smaller than {approx} 70 {micro}m region of K{sub {alpha}} emission. 2D particle-in-cell (PIC) simulations suggest that the surface heating is due to a light pressure driven shock.
Date: May 4, 2007
Creator: Akli, K; Hansen, S B; Kemp, A J; Freeman, R R; Beg, F N; Clark, D et al.
Partner: UNT Libraries Government Documents Department

Nail-like targets for laser plasma interaction experiments

Description: The interaction of ultra-high power picosecond laser pulses with solid targets is of interest both for benchmarking the results of hybrid particle in cell (PIC) codes and also for applications to re-entrant cone guided fast ignition. We describe the construction of novel targets in which copper/titanium wires are formed into 'nail-like' objects by a process of melting and micromachining, so that energy can be reliably coupled to a 24 {micro}m diameter wire. An extreme-ultraviolet image of the interaction of the Titan laser with such a target is shown.
Date: December 18, 2007
Creator: Pasley, J; Wei, M; Shipton, E; Chen, S; Ma, T; Beg, F N et al.
Partner: UNT Libraries Government Documents Department

Limitation on Pre-pulse Level for Cone-Guided Fast-Ignition ICF

Description: The viability of fast-ignition (FI) inertial confinement fusion hinges on the efficient transfer of laser energy to the compressed fuel via multi-MeV electrons. Pre-formed plasma due to laser pre-pulse strongly influences ultra-intense laser plasma interactions and hot electron generation in the hollow cone of an FI target. We induced a prepulse and consequent preplasma in copper cone targets and measured the energy deposition zone of the main pulse by imaging the emitted K{sub {alpha}} radiation. An integrated simulation of radiation hydrodynamics for the pre-plasma and particle in cell for the main pulse interactions agree well with the measured deposition zones and provide an insight into the enrgy deposition mechanism and electron distribution. It was demonstrated that a under these conditions a 100mJ pre-pulse completely eliminates the forward going component of {approx}2-4MeV electrons. Consequences for cone-guided fast-ignition are discussed.
Date: September 1, 2009
Creator: MacPhee, A G; Akli, K U; Beg, F N; Chen, C D; Chen, H; Divol, L et al.
Partner: UNT Libraries Government Documents Department

Titanium K-Shell X-Ray Production from High Velocity Wire Arrays Implosions on the 20-MA Z Accelerator

Description: The advent of the 20-MA Z accelerator [R.B. Spielman, C. Deeney, G.A. Chandler, et al., Phys. Plasmas 5, 2105, (1997)] has enabled implosions of large diameter, high-wire-number arrays of titanium to begin testing Z-pinch K-shell scaling theories. The 2-cm long titanium arrays, which were mounted on a 40-mm diameter, produced between 75{+-}15 to 125{+-}20 kJ of K-shell x-rays. Mass scans indicate that, as predicted, higher velocity implosions in the series produced higher x-ray yields. Spectroscopic analyses indicate that these high velocity implosions achieved peak electron temperatures from 2.7{+-}0.1 to 3.2{+-}0.2 keV and obtained a K-shell emission mass participation of up to 12%.
Date: January 27, 1999
Creator: Apruzese, J.P.; Beg, F.N.; Clark, R.C.; Coverdale, C.A.; Davis, J.; Deeney, C. et al.
Partner: UNT Libraries Government Documents Department

On Point Designs for High Gain Fast Ignition

Description: Fast ignition research has reached the stage where point designs are becoming crucial to the identification of key issues and the development of projects to demonstrate high gain fast ignition. The status of point designs for cone coupled electron fast ignition and some of the issues they highlight are discussed.
Date: September 27, 2007
Creator: Key, M; Akli, K; Beg, F; Betti, R; Clark, D S; Chen, S N et al.
Partner: UNT Libraries Government Documents Department

A Dual Channel X-ray Spectrometer for Fast Ignition Research

Description: A new Dual Channel Highly Ordered Pyrolytic Graphite (DC-HOPG) x-ray spectrometer was developed to study laser-generated electron beam transport. The instrument uses a pair of graphite crystals and has the advantage of simultaneously detecting self emission from low-Z materials in first diffraction order and high-Z materials in second order. The emissions from the target are detected using a pair of parallel imaging plates positioned in a such way that the noise from background is minimized and the mosaic focusing is achieved. Initial tests of the diagnostic on Titan laser (I {approx} 10{sup 20} W/cm{sup 2}, {tau} = 0.7 ps) show excellent signal-to-noise ratio (SNR) > 1000 for the low energy channel and SNR > 400 for the high energy channel.
Date: April 19, 2010
Creator: Akli, K U; Patel, P K; Van Maren, R; Stephens, R B; Key, M H; Higginson, D P et al.
Partner: UNT Libraries Government Documents Department

Studies of electron and proton isochoric heating for fast ignition

Description: Isochoric heating of inertially confined fusion plasmas by laser driven MeV electrons or protons is an area of great topical interest in the inertial confinement fusion community, particularly with respect to the fast ignition (FI) proposal to use this technique to initiate burn in a fusion capsule. Experiments designed to investigate electron isochoric heating have measured heating in two limiting cases of interest to fast ignition, small planar foils and hollow cones. Data from Cu K{alpha} fluorescence, crystal x-ray spectroscopy of Cu K shell emission, and XUV imaging at 68eV and 256 eV are used to test PIC and Hybrid PIC modeling of the interaction. Isochoric heating by focused proton beams generated at the concave inside surface of a hemi-shell and from a sub hemi-shell inside a cone have been studied with the same diagnostic methods plus imaging of proton induced K{alpha}. Conversion efficiency to protons has also been measured and modeled. Conclusions from the proton and electron heating experiments will be presented. Recent advances in modeling electron transport and innovative target designs for reducing igniter energy and increasing gain curves will also be discussed.
Date: October 2, 2006
Creator: Mackinnon, A.; Key, M.; Akli, K.; Beg, F.; Clarke, R.; Clarke, D. et al.
Partner: UNT Libraries Government Documents Department

Hot Electron Generation and Transport Using K(alpha) Emission

Description: We have conducted experiments on both the Vulcan and Titan laser facilities to study hot electron generation and transport in the context of fast ignition. Cu wires attached to Al cones were used to investigate the effect on coupling efficiency of plasma surround and the pre-formed plasma inside the cone. We found that with thin cones 15% of laser energy is coupled to the 40{micro}m diameter wire emulating a 40{micro}m fast ignition spot. Thick cone walls, simulating plasma in fast ignition, reduce coupling by x4. An increase of prepulse level inside the cone by a factor of 50 reduces coupling by a factor of 3.
Date: October 15, 2009
Creator: Akli, K U; Stephens, R B; Key, M H; Bartal, T; Beg, F N; Chawla, S et al.
Partner: UNT Libraries Government Documents Department

Overview of recent progress in US fast ignition research

Description: The Fast Ignition Program in the United States has enjoyed increased funding in various forms from the Office of Fusion Energy Sciences of the Department of Energy. The program encompasses experiments on large laser facilities at various world-wide locations, and benefits enormously from collaborations with many international scientists. The program includes exploratory work in cone-target design and implosion dynamics, high electron current transport measurements in normal density materials, development of diagnostics for heating measurements, generation of protons from shaped targets, theoretical work on high gain target designs, and extensive modeling development using PIC and hybrid codes.
Date: September 28, 2005
Creator: Freeman, R. R.; Akli, K.; Beg, F.; Betti, R.; Chen, S.; Clark, D. J. et al.
Partner: UNT Libraries Government Documents Department