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Pak A, Khoolenjani NB, Jafari AA. Inference on P(Y < X)in Bivariate Rayleigh Distribution. COMMUN STAT-THEOR M 2014. [DOI: 10.1080/03610926.2012.730165] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Gauthier M, Fletcher LB, Ravasio A, Galtier E, Gamboa EJ, Granados E, Hastings JB, Heimann P, Lee HJ, Nagler B, Schropp A, Gleason A, Döppner T, LePape S, Ma T, Pak A, MacDonald MJ, Ali S, Barbrel B, Falcone R, Kraus D, Chen Z, Mo M, Wei M, Glenzer SH. New experimental platform to study high density laser-compressed matter. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2014; 85:11E616. [PMID: 25430362 DOI: 10.1063/1.4896175] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We have developed a new experimental platform at the Linac Coherent Light Source (LCLS) which combines simultaneous angularly and spectrally resolved x-ray scattering measurements. This technique offers a new insights on the structural and thermodynamic properties of warm dense matter. The < 50 fs temporal duration of the x-ray pulse provides near instantaneous snapshots of the dynamics of the compression. We present a proof of principle experiment for this platform to characterize a shock-compressed plastic foil. We observe the disappearance of the plastic semi-crystal structure and the formation of a compressed liquid ion-ion correlation peak. The plasma parameters of shock-compressed plastic can be measured as well, but requires an averaging over a few tens of shots.
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Merrill FE, Danly CR, Izumi N, Jedlovec D, Fittinghoff DN, Grim GP, Pak A, Park HS, Volegov PL, Wilde CH. A concept to collect neutron and x-ray images on the same line of sight at NIF. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2014; 85:11E614. [PMID: 25430360 DOI: 10.1063/1.4891101] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Neutron and x-ray images are collected at the National Ignition Facility (NIF) to measure the size and shape of inertial confinement fusion implosions. The x-ray images provide a measure of the size and shape of the hot region of the deuterium-tritium fuel while the neutron images provide a measure of the size and shape of the burning plasma. Although these two types of images are collected simultaneously, they are not collected along the same line of sight (LOS). One 14 MeV neutron image is collected on the NIF equator, and two x-ray images are collected along the polar axis and nearly perpendicular to the neutron imaging line of sight on the equator. Both measurements use pinhole apertures to form the images, but existing x-ray imaging provides time-resolved measurements while the neutron images are time-integrated. Detailed comparisons of the x-ray and neutron images can provide information on the fuel assembly, but these studies have been limited because the implosions are not azimuthally symmetric and the images are collected along different LOS. We have developed a conceptual design of a time-integrated x-ray imaging system that could be added to the existing neutron imaging LOS. This new system would allow these detailed studies, providing important information on the fuel assembly of future implosions. Here we present this conceptual design and the expected performance characteristics.
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Döppner T, Kritcher AL, Neumayer P, Kraus D, Bachmann B, Burns S, Falcone RW, Glenzer SH, Hawreliak J, House A, Landen OL, LePape S, Ma T, Pak A, Swift D. Qualification of a high-efficiency, gated spectrometer for x-ray Thomson scattering on the National Ignition Facility. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2014; 85:11D617. [PMID: 25430193 DOI: 10.1063/1.4890253] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We have designed, built, and successfully fielded a highly efficient and gated Bragg crystal spectrometer for x-ray Thomson scattering measurements on the National Ignition Facility (NIF). It utilizes a cylindrically curved Highly Oriented Pyrolytic Graphite crystal. Its spectral range of 7.4-10 keV is optimized for scattering experiments using a Zn He-α x-ray probe at 9.0 keV or Mo K-shell line emission around 18 keV in second diffraction order. The spectrometer has been designed as a diagnostic instrument manipulator-based instrument for the NIF target chamber at the Lawrence Livermore National Laboratory, USA. Here, we report on details of the spectrometer snout, its novel debris shield configuration and an in situ spectral calibration experiment with a Brass foil target, which demonstrated a spectral resolution of E/ΔE = 220 at 9.8 keV.
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Pak A, Field JE, Benedetti LR, Caggiano J, Hatarik R, Izumi N, Khan SF, Knauer J, Ma T, Spears BK, Town RPJ, Bradley DK. Diagnosing residual motion via the x-ray self emission from indirectly driven inertial confinement implosions. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2014; 85:11E605. [PMID: 25430351 DOI: 10.1063/1.4890259] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
In an indirectly driven implosion, non-radial translational motion of the compressed fusion capsule is a signature of residual kinetic energy not coupled into the compressional heating of the target. A reduction in compression reduces the peak pressure and nuclear performance of the implosion. Measuring and reducing the residual motion of the implosion is therefore necessary to improve performance and isolate other effects that degrade performance. Using the gated x-ray diagnostic, the x-ray Bremsstrahlung emission from the compressed capsule is spatially and temporally resolved at x-ray energies of >8.7 keV, allowing for measurements of the residual velocity. Here details of the x-ray velocity measurement and fitting routine will be discussed and measurements will be compared to the velocities inferred from the neutron time of flight detectors.
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Fletcher LB, Lee HJ, Barbrel B, Gauthier M, Galtier E, Nagler B, Döppner T, LePape S, Ma T, Pak A, Turnbull D, White T, Gregori G, Wei M, Falcone RW, Heimann P, Zastrau U, Hastings JB, Glenzer SH. Exploring Mbar shock conditions and isochorically heated aluminum at the Matter in Extreme Conditions end station of the Linac Coherent Light Source (invited). THE REVIEW OF SCIENTIFIC INSTRUMENTS 2014; 85:11E702. [PMID: 25430365 DOI: 10.1063/1.4891186] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Recent experiments performed at the Matter in Extreme Conditions end station of the Linac Coherent Light Source (LCLS) have demonstrated the first spectrally resolved measurements of plasmons from isochorically heated aluminum. The experiments have been performed using a seeded 8-keV x-ray laser beam as a pump and probe to both volumetrically heat and scatter x-rays from aluminum. Collective x-ray Thomson scattering spectra show a well-resolved plasmon feature that is down-shifted in energy by 19 eV. In addition, Mbar shock pressures from laser-compressed aluminum foils using velocity interferometer system for any reflector have been measured. The combination of experiments fully demonstrates the possibility to perform warm dense matter studies at the LCLS with unprecedented accuracy and precision.
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Field JE, Rygg JR, Barrios MA, Benedetti LR, Döppner T, Izumi N, Jones O, Khan SF, Ma T, Nagel SR, Pak A, Tommasini R, Bradley DK, Town RPJ. Reconstruction of 2D x-ray radiographs at the National Ignition Facility using pinhole tomography (invited). THE REVIEW OF SCIENTIFIC INSTRUMENTS 2014; 85:11E503. [PMID: 25430345 DOI: 10.1063/1.4890395] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Two-dimensional radiographs of imploding fusion capsules are obtained at the National Ignition Facility by projection through a pinhole array onto a time-gated framing camera. Parallax among images in the image array makes it possible to distinguish contributions from the capsule and from the backlighter, permitting correction of backlighter non-uniformities within the capsule radiograph. Furthermore, precise determination of the imaging system geometry and implosion velocity enables combination of multiple images to reduce signal-to-noise and discover new capsule features.
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Hurricane OA, Callahan DA, Casey DT, Celliers PM, Cerjan C, Dewald EL, Dittrich TR, Döppner T, Hinkel DE, Hopkins LFB, Kline JL, LePape S, Ma T, MacPhee AG, Milovich JL, Pak A, Park HS, Patel PK, Remington BA, Salmonson JD, Springer PT, Tommasini R. Erratum: Corrigendum: Fuel gain exceeding unity in an inertially confined fusion implosion. Nature 2014. [DOI: 10.1038/nature13533] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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59
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Le Pape S, Divol L, Berzak Hopkins L, Mackinnon A, Meezan NB, Casey D, Frenje J, Herrmann H, McNaney J, Ma T, Widmann K, Pak A, Grimm G, Knauer J, Petrasso R, Zylstra A, Rinderknecht H, Rosenberg M, Gatu-Johnson M, Kilkenny JD. Observation of a reflected shock in an indirectly driven spherical implosion at the national ignition facility. PHYSICAL REVIEW LETTERS 2014; 112:225002. [PMID: 24949774 DOI: 10.1103/physrevlett.112.225002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2013] [Indexed: 06/03/2023]
Abstract
A 200 μm radius hot spot at more than 2 keV temperature, 1 g/cm^{3} density has been achieved on the National Ignition Facility using a near vacuum hohlraum. The implosion exhibits ideal one-dimensional behavior and 99% laser-to-hohlraum coupling. The low opacity of the remaining shell at bang time allows for a measurement of the x-ray emission of the reflected central shock in a deuterium plasma. Comparison with 1D hydrodynamic simulations puts constraints on electron-ion collisions and heat conduction. Results are consistent with classical (Spitzer-Harm) heat flux.
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Rygg JR, Jones OS, Field JE, Barrios MA, Benedetti LR, Collins GW, Eder DC, Edwards MJ, Kline JL, Kroll JJ, Landen OL, Ma T, Pak A, Peterson JL, Raman K, Town RPJ, Bradley DK. 2D X-ray radiography of imploding capsules at the national ignition facility. PHYSICAL REVIEW LETTERS 2014; 112:195001. [PMID: 24877944 DOI: 10.1103/physrevlett.112.195001] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Indexed: 06/03/2023]
Abstract
First measurements of the in-flight shape of imploding inertial confinement fusion (ICF) capsules at the National Ignition Facility (NIF) were obtained by using two-dimensional x-ray radiography. The sequence of area-backlit, time-gated pinhole images is analyzed for implosion velocity, low-mode shape and density asymmetries, and the absolute offset and center-of-mass velocity of the capsule shell. The in-flight shell is often observed to be asymmetric even when the concomitant core self-emission is round. A ∼ 15 μm shell asymmetry amplitude of the Y(40) spherical harmonic mode was observed for standard NIF ICF hohlraums at a shell radius of ∼ 200 μm (capsule at ∼ 5× radial compression). This asymmetry is mitigated by a ∼ 10% increase in the hohlraum length.
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Fletcher LB, Kritcher AL, Pak A, Ma T, Döppner T, Fortmann C, Divol L, Jones OS, Landen OL, Scott HA, Vorberger J, Chapman DA, Gericke DO, Mattern BA, Seidler GT, Gregori G, Falcone RW, Glenzer SH. Observations of continuum depression in warm dense matter with x-ray Thomson scattering. PHYSICAL REVIEW LETTERS 2014; 112:145004. [PMID: 24765979 DOI: 10.1103/physrevlett.112.145004] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2013] [Indexed: 06/03/2023]
Abstract
Detailed measurements of the electron densities, temperatures, and ionization states of compressed CH shells approaching pressures of 50 Mbar are achieved with spectrally resolved x-ray scattering. Laser-produced 9 keV x-rays probe the plasma during the transient state of three-shock coalescence. High signal-to-noise x-ray scattering spectra show direct evidence of continuum depression in highly degenerate warm dense matter states with electron densities ne>1024 cm-3. The measured densities and temperatures agree well with radiation-hydrodynamic modeling when accounting for continuum lowering in calculations that employ detailed configuration accounting.
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Hurricane OA, Callahan DA, Casey DT, Celliers PM, Cerjan C, Dewald EL, Dittrich TR, Döppner T, Hinkel DE, Hopkins LFB, Kline JL, Le Pape S, Ma T, MacPhee AG, Milovich JL, Pak A, Park HS, Patel PK, Remington BA, Salmonson JD, Springer PT, Tommasini R. Fuel gain exceeding unity in an inertially confined fusion implosion. Nature 2014; 506:343-8. [DOI: 10.1038/nature13008] [Citation(s) in RCA: 660] [Impact Index Per Article: 66.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2013] [Accepted: 01/07/2014] [Indexed: 11/09/2022]
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63
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Smalyuk VA, Tipton RE, Pino JE, Casey DT, Grim GP, Remington BA, Rowley DP, Weber SV, Barrios M, Benedetti LR, Bleuel DL, Bradley DK, Caggiano JA, Callahan DA, Cerjan CJ, Clark DS, Edgell DH, Edwards MJ, Frenje JA, Gatu-Johnson M, Glebov VY, Glenn S, Haan SW, Hamza A, Hatarik R, Hsing WW, Izumi N, Khan S, Kilkenny JD, Kline J, Knauer J, Landen OL, Ma T, McNaney JM, Mintz M, Moore A, Nikroo A, Pak A, Parham T, Petrasso R, Sayre DB, Schneider MB, Tommasini R, Town RP, Widmann K, Wilson DC, Yeamans CB. Measurements of an ablator-gas atomic mix in indirectly driven implosions at the National Ignition Facility. PHYSICAL REVIEW LETTERS 2014; 112:025002. [PMID: 24484021 DOI: 10.1103/physrevlett.112.025002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2013] [Indexed: 06/03/2023]
Abstract
We present the first results from an experimental campaign to measure the atomic ablator-gas mix in the deceleration phase of gas-filled capsule implosions on the National Ignition Facility. Plastic capsules containing CD layers were filled with tritium gas; as the reactants are initially separated, DT fusion yield provides a direct measure of the atomic mix of ablator into the hot spot gas. Capsules were imploded with x rays generated in hohlraums with peak radiation temperatures of ∼294 eV. While the TT fusion reaction probes conditions in the central part (core) of the implosion hot spot, the DT reaction probes a mixed region on the outer part of the hot spot near the ablator-hot-spot interface. Experimental data were used to develop and validate the atomic-mix model used in two-dimensional simulations.
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64
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Albert F, Pollock BB, Shaw JL, Marsh KA, Ralph JE, Chen YH, Alessi D, Pak A, Clayton CE, Glenzer SH, Joshi C. Angular dependence of betatron x-ray spectra from a laser-wakefield accelerator. PHYSICAL REVIEW LETTERS 2013; 111:235004. [PMID: 24476282 DOI: 10.1103/physrevlett.111.235004] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2013] [Indexed: 06/03/2023]
Abstract
We present the first measurements of the angular dependence of the betatron x-ray spectrum produced by electrons inside the cavity of a laser-wakefield accelerator. Electrons accelerated up to 300 MeV energies produce a beam of broadband, forward-directed betatron x-ray radiation extending up to 80 keV. The angular resolved spectrum from an image plate-based spectrometer with differential filtering provides data in a single laser shot. The simultaneous spectral and spatial x-ray analysis allows for a three-dimensional reconstruction of electron trajectories with micrometer resolution, and we find that the angular dependence of the x-ray spectrum is showing strong evidence of anisotropic electron trajectories.
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Dewald EL, Milovich JL, Michel P, Landen OL, Kline JL, Glenn S, Jones O, Kalantar DH, Pak A, Robey HF, Kyrala GA, Divol L, Benedetti LR, Holder J, Widmann K, Moore A, Schneider MB, Döppner T, Tommasini R, Bradley DK, Bell P, Ehrlich B, Thomas CA, Shaw M, Widmayer C, Callahan DA, Meezan NB, Town RPJ, Hamza A, Dzenitis B, Nikroo A, Moreno K, Van Wonterghem B, Mackinnon AJ, Glenzer SH, MacGowan BJ, Kilkenny JD, Edwards MJ, Atherton LJ, Moses EI. Early-time symmetry tuning in the presence of cross-beam energy transfer in ICF experiments on the National Ignition Facility. PHYSICAL REVIEW LETTERS 2013; 111:235001. [PMID: 24476279 DOI: 10.1103/physrevlett.111.235001] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2013] [Indexed: 06/03/2023]
Abstract
On the National Ignition Facility, the hohlraum-driven implosion symmetry is tuned using cross-beam energy transfer (CBET) during peak power, which is controlled by applying a wavelength separation between cones of laser beams. In this Letter, we present early-time measurements of the instantaneous soft x-ray drive at the capsule using reemission spheres, which show that this wavelength separation also leads to significant CBET during the first shock, even though the laser intensities are 30× smaller than during the peak. We demonstrate that the resulting early drive P2/P0 asymmetry can be minimized and tuned to <1% accuracy (well within the ±7.5% requirement for ignition) by varying the relative input powers between different cones of beams. These experiments also provide time-resolved measurements of CBET during the first 2 ns of the laser drive, which are in good agreement with radiation-hydrodynamics calculations including a linear CBET model.
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66
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Smalyuk VA, Atherton LJ, Benedetti LR, Bionta R, Bleuel D, Bond E, Bradley DK, Caggiano J, Callahan DA, Casey DT, Celliers PM, Cerjan CJ, Clark D, Dewald EL, Dixit SN, Döppner T, Edgell DH, Edwards MJ, Frenje J, Gatu-Johnson M, Glebov VY, Glenn S, Glenzer SH, Grim G, Haan SW, Hammel BA, Hartouni EP, Hatarik R, Hatchett S, Hicks DG, Hsing WW, Izumi N, Jones OS, Key MH, Khan SF, Kilkenny JD, Kline JL, Knauer J, Kyrala GA, Landen OL, Le Pape S, Lindl JD, Ma T, MacGowan BJ, Mackinnon AJ, MacPhee AG, McNaney J, Meezan NB, Moody JD, Moore A, Moran M, Moses EI, Pak A, Parham T, Park HS, Patel PK, Petrasso R, Ralph JE, Regan SP, Remington BA, Robey HF, Ross JS, Spears BK, Springer PT, Suter LJ, Tommasini R, Town RP, Weber SV, Widmann K. Performance of high-convergence, layered DT implosions with extended-duration pulses at the National Ignition Facility. PHYSICAL REVIEW LETTERS 2013; 111:215001. [PMID: 24313493 DOI: 10.1103/physrevlett.111.215001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2013] [Indexed: 06/02/2023]
Abstract
Radiation-driven, low-adiabat, cryogenic DT layered plastic capsule implosions were carried out on the National Ignition Facility (NIF) to study the sensitivity of performance to peak power and drive duration. An implosion with extended drive and at reduced peak power of 350 TW achieved the highest compression with fuel areal density of ~1.3±0.1 g/cm2, representing a significant step from previously measured ~1.0 g/cm2 toward a goal of 1.5 g/cm2. Future experiments will focus on understanding and mitigating hydrodynamic instabilities and mix, and improving symmetry required to reach the threshold for thermonuclear ignition on NIF.
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67
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Ma T, Patel PK, Izumi N, Springer PT, Key MH, Atherton LJ, Benedetti LR, Bradley DK, Callahan DA, Celliers PM, Cerjan CJ, Clark DS, Dewald EL, Dixit SN, Döppner T, Edgell DH, Epstein R, Glenn S, Grim G, Haan SW, Hammel BA, Hicks D, Hsing WW, Jones OS, Khan SF, Kilkenny JD, Kline JL, Kyrala GA, Landen OL, Le Pape S, MacGowan BJ, Mackinnon AJ, MacPhee AG, Meezan NB, Moody JD, Pak A, Parham T, Park HS, Ralph JE, Regan SP, Remington BA, Robey HF, Ross JS, Spears BK, Smalyuk V, Suter LJ, Tommasini R, Town RP, Weber SV, Lindl JD, Edwards MJ, Glenzer SH, Moses EI. Onset of hydrodynamic mix in high-velocity, highly compressed inertial confinement fusion implosions. PHYSICAL REVIEW LETTERS 2013; 111:085004. [PMID: 24010449 DOI: 10.1103/physrevlett.111.085004] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2013] [Indexed: 06/02/2023]
Abstract
Deuterium-tritium inertial confinement fusion implosion experiments on the National Ignition Facility have demonstrated yields ranging from 0.8 to 7×10(14), and record fuel areal densities of 0.7 to 1.3 g/cm2. These implosions use hohlraums irradiated with shaped laser pulses of 1.5-1.9 MJ energy. The laser peak power and duration at peak power were varied, as were the capsule ablator dopant concentrations and shell thicknesses. We quantify the level of hydrodynamic instability mix of the ablator into the hot spot from the measured elevated absolute x-ray emission of the hot spot. We observe that DT neutron yield and ion temperature decrease abruptly as the hot spot mix mass increases above several hundred ng. The comparison with radiation-hydrodynamic modeling indicates that low mode asymmetries and increased ablator surface perturbations may be responsible for the current performance.
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68
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Ma T, Döppner T, Falcone RW, Fletcher L, Fortmann C, Gericke DO, Landen OL, Lee HJ, Pak A, Vorberger J, Wünsch K, Glenzer SH. X-ray scattering measurements of strong ion-ion correlations in shock-compressed aluminum. PHYSICAL REVIEW LETTERS 2013; 110:065001. [PMID: 23432260 DOI: 10.1103/physrevlett.110.065001] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2012] [Revised: 11/19/2012] [Indexed: 06/01/2023]
Abstract
The strong ion-ion correlation peak characteristic of warm dense matter (WDM) is observed for the first time using simultaneous angularly, temporally, and spectrally resolved x-ray scattering measurements in laser-driven shock-compressed aluminum. Laser-produced molybdenum x-ray line emission at an energy of 17.9 keV is employed to probe aluminum compressed to a density of ρ>8 g/cm(3). We observe a well pronounced peak in the static structure factor at a wave number of k=4.0 Å(-1). The measurements of the magnitude and position of this correlation peak are precise enough to test different theoretical models for the ion structure and show that only models taking the complex interaction in WDM into account agree with the data. This also demonstrates a new highly accurate diagnostic to directly measure the state of compression of warm dense matter.
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69
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Pak A, Divol L, Weber S, Döppner T, Kyrala GA, Kilne J, Izumi N, Glenn S, Ma T, Town RP, Bradley DK, Glenzer SH. Diagnosing radiative shocks from deuterium and tritium implosions on NIF. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2012; 83:10E507. [PMID: 23127014 DOI: 10.1063/1.4729498] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
During the recent ignition tuning campaign at the National Ignition Facility, layered cryogenic deuterium and tritium capsules were imploded via x-ray driven ablation. The hardened gated x-ray imager diagnostic temporally and spatially resolves the x-ray emission from the core of the capsule implosion at energies above ~8 keV. On multiple implosions, ~200-400 ps after peak compression a spherically expanding radiative shock has been observed. This paper describes the methods used to characterize the radial profile and rate of expansion of the shock induced x-ray emission.
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70
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Pak A, Bernhard D, Paroubek P, Grouin C. A combined approach to emotion detection in suicide notes. BIOMEDICAL INFORMATICS INSIGHTS 2012; 5:105-14. [PMID: 22879766 PMCID: PMC3409479 DOI: 10.4137/bii.s8969] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
In this paper, we present the system we have developed for participating in the second task of the i2b2/VA 2011 challenge dedicated to emotion detection in clinical records. On the official evaluation, we ranked 6th out of 26 participants. Our best configuration, based upon a combination of both a machine-learning based approach and manually-defined transducers, obtained a 0.5383 global F-measure, while the distribution of the other 26 participants' results is characterized by mean = 0.4875, stdev = 0.0742, min = 0.2967, max = 0.6139, and median = 0.5027. Combination of machine learning and transducer is achieved by computing the union of results from both approaches, each using a hierarchy of sentiment specific classifiers.
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71
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Pollock BB, Clayton CE, Ralph JE, Albert F, Davidson A, Divol L, Filip C, Glenzer SH, Herpoldt K, Lu W, Marsh KA, Meinecke J, Mori WB, Pak A, Rensink TC, Ross JS, Shaw J, Tynan GR, Joshi C, Froula DH. Demonstration of a narrow energy spread, ∼0.5 GeV electron beam from a two-stage laser wakefield accelerator. PHYSICAL REVIEW LETTERS 2011; 107:045001. [PMID: 21867013 DOI: 10.1103/physrevlett.107.045001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2011] [Indexed: 05/31/2023]
Abstract
Laser wakefield acceleration of electrons holds great promise for producing ultracompact stages of GeV scale, high-quality electron beams for applications such as x-ray free electron lasers and high-energy colliders. Ultrahigh intensity laser pulses can be self-guided by relativistic plasma waves (the wake) over tens of vacuum diffraction lengths, to give >1 GeV energy in centimeter-scale low density plasmas using ionization-induced injection to inject charge into the wake even at low densities. By restricting electron injection to a distinct short region, the injector stage, energetic electron beams (of the order of 100 MeV) with a relatively large energy spread are generated. Some of these electrons are then further accelerated by a second, longer accelerator stage, which increases their energy to ∼0.5 GeV while reducing the relative energy spread to <5% FWHM.
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Clayton CE, Ralph JE, Albert F, Fonseca RA, Glenzer SH, Joshi C, Lu W, Marsh KA, Martins SF, Mori WB, Pak A, Tsung FS, Pollock BB, Ross JS, Silva LO, Froula DH. Self-guided laser wakefield acceleration beyond 1 GeV using ionization-induced injection. PHYSICAL REVIEW LETTERS 2010; 105:105003. [PMID: 20867526 DOI: 10.1103/physrevlett.105.105003] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2010] [Indexed: 05/29/2023]
Abstract
The concepts of matched-beam, self-guided laser propagation and ionization-induced injection have been combined to accelerate electrons up to 1.45 GeV energy in a laser wakefield accelerator. From the spatial and spectral content of the laser light exiting the plasma, we infer that the 60 fs, 110 TW laser pulse is guided and excites a wake over the entire 1.3 cm length of the gas cell at densities below 1.5 × 10(18) cm(-3). High-energy electrons are observed only when small (3%) amounts of CO2 gas are added to the He gas. Computer simulations confirm that it is the K-shell electrons of oxygen that are ionized and injected into the wake and accelerated to beyond 1 GeV energy.
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73
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Pak A, Marsh KA, Martins SF, Lu W, Mori WB, Joshi C. Injection and trapping of tunnel-ionized electrons into laser-produced wakes. PHYSICAL REVIEW LETTERS 2010; 104:025003. [PMID: 20366604 DOI: 10.1103/physrevlett.104.025003] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2009] [Indexed: 05/29/2023]
Abstract
A method, which utilizes the large difference in ionization potentials between successive ionization states of trace atoms, for injecting electrons into a laser-driven wakefield is presented. Here a mixture of helium and trace amounts of nitrogen gas was used. Electrons from the K shell of nitrogen were tunnel ionized near the peak of the laser pulse and were injected into and trapped by the wake created by electrons from majority helium atoms and the L shell of nitrogen. The spectrum of the accelerated electrons, the threshold intensity at which trapping occurs, the forward transmitted laser spectrum, and the beam divergence are all consistent with this injection process. The experimental measurements are supported by theory and 3D OSIRIS simulations.
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Froula DH, Clayton CE, Döppner T, Marsh KA, Barty CPJ, Divol L, Fonseca RA, Glenzer SH, Joshi C, Lu W, Martins SF, Michel P, Mori WB, Palastro JP, Pollock BB, Pak A, Ralph JE, Ross JS, Siders CW, Silva LO, Wang T. Measurements of the critical power for self-injection of electrons in a laser wakefield accelerator. PHYSICAL REVIEW LETTERS 2009; 103:215006. [PMID: 20366048 DOI: 10.1103/physrevlett.103.215006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2009] [Indexed: 05/29/2023]
Abstract
A laser wakefield acceleration study has been performed in the matched, self-guided, blowout regime producing 720 +/- 50 MeV quasimonoenergetic electrons with a divergence Deltatheta_{FWHM} of 2.85 +/- 0.15 mrad using a 10 J, 60 fs 0.8 microm laser. While maintaining a nearly constant plasma density (3 x 10{18} cm{-3}), the energy gain increased from 75 to 720 MeV when the plasma length was increased from 3 to 8 mm. Absolute charge measurements indicate that self-injection of electrons occurs when the laser power P exceeds 3 times the critical power P{cr} for relativistic self-focusing and saturates around 100 pC for P/P{cr} > 5. The results are compared with both analytical scalings and full 3D particle-in-cell simulations.
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Borkon A, Kao A, Stuart S, Daon E, Zorn G, Pak A, Allen K. 362: Biatrial Implantation with Modified Cabrol Technique Provides Similar Outcomes Compared to Bicaval Anastomosis. J Heart Lung Transplant 2009. [DOI: 10.1016/j.healun.2008.11.369] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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