Bulletin of the American Physical Society
57th Annual Meeting of the APS Division of Plasma Physics
Volume 60, Number 19
Monday–Friday, November 16–20, 2015; Savannah, Georgia
Session TO4: X-Ray Sources and Diagnostics |
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Chair: Arati Dasgupta, Naval Research Laboratory Room: 105/106 |
Thursday, November 19, 2015 9:30AM - 9:42AM |
TO4.00001: Creation of ultra-high energy density matter using nanostructured targets J. Park, Riccardo Tommasini, R. London, H. Chen, R.C. Hollinger, C. Bargsten, V. Shlyaptsev, M. Capeluto, D. Keiss, A. Townsend, J.J. Rocca, V. Kaymak, A. Pukhov, M. Hill Recent experiments have demonstrated that trapping of 60 femtosecond laser pulses of relativistic intensity deep within ordered nanowire arrays can create a new ultra-hot plasma regime. [1] Here we report on the experiments at the Titan laser at the Lawrence Livermore National Laboratory that aim to scale these results by two orders of magnitude in laser energy. Preliminary analysis of the Titan results show that sub-picosecond laser irradiation of vertically aligned nanostructures of Au, Ag and Ni produces an increase of a factor greater than 1.6 in the suprathermal electron temperatures and an increase by a factor of 3 in the conversion efficiency into continuum x-rays, both with respect to flat targets of the same composition. K$_{\alpha}$ radiation from nanowire array targets also shows an increase between 3x and 5x over flat targets. The nanowire array targets reflected a 5x smaller fraction of the laser energy, indicating significantly larger absorption of the laser pulse. This work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344, by the Office of Fusion Energy Sciences, U.S Department of Energy, and by the Defense Threat Reduction Agency grant HDTRA-1-10-1-0079. [1] M. A. Purvis, et al., Nature Photonics 7, 796 (2013) [Preview Abstract] |
Thursday, November 19, 2015 9:42AM - 9:54AM |
TO4.00002: Unique X-ray emission characteristics from volumetrically heated nanowire array plasmas J.J. Rocca, C. Bargsten, R. Hollinger, V. Shlyaptsev, A. Pukhov, V. Kaymak, G. Capeluto, D. Keiss, A. Townsend, A. Rockwood, Y. Wang, S. Wang Highly anisotropic emission of hard X-ray radiation (h$\nu $ \textgreater 10 keV) is observed when arrays of ordered nanowires (50 nm diameter wires of Au or Ni [1]) are volumetrically heated by normal incidence irradiation with high contrast 50-60 fs laser pulses of relativistic intensity. The annular emission is in contrast with angular distribution of softer X-rays (h$\nu $ \textgreater 1 KeV) from these targets and with the X-ray radiation emitted by polished flat targets, both of which are nearly isotropic. Model computations that make use the electron energy distribution computed by particle-in-cell simulations show that the unexpected annular distribution of the hard x-rays is the result of bremsstrahlung from fast electrons. Volumetric heating of Au nanowire arrays irradiated with an intensity of 2 x 10 19 W cm-2 is measured to convert laser energy into h$\nu $\textgreater 1KeV photons with a record efficiency of \textgreater 8 percent into 2$\pi$, creating a bright picosecond X-ray source for applications. \\[4pt] [1] M.Purvis et al. Nature Photonics 7, 796 (2013). [Preview Abstract] |
Thursday, November 19, 2015 9:54AM - 10:06AM |
TO4.00003: Time limit for the efficient coupling of relativistic femtosecond laser pulses into aligned nanowire arrays R. Hollinger, C. Bargsten, V. Shlyaptsev, D. Keiss, A. Townsend, A. Rockwood, Y. Wang, S. Wang, J.J. Rocca, A. Pukhov, V. Kaymak, R. London, R. Tommasini Recent experiments at Colorado State University have demonstrated volumetric heating of near solid density plasmas to multi-keV temperatures by intense high contrast femtosecond laser irradiation of vertically aligned nanostructures [1]. A key parameter is the time for the heated nanowires to expand and fill the inter-wire gaps with a super-critical density plasma. After this time the laser light can no longer penetrate deep into the array, effectively terminating volumetric heating. We have gained information on the gap closure time for arrays with different wire spacing by monitoring the intensity of He-like lines from arrays of nickel nanowires while varying the laser pulse width from 50 fs to 250 fs. Experiments conducted at constant laser energy show that He-like $\alpha $ line emission from arrays of 80 nm diameter nanowires separated by 205 nm is observed for pulse widths of 200 fs. It is possible to find an optimal wire separation to match the pulse width of the driving laser. The results are relevant to scaling the scheme to high energy laser facilities that are characterized by longer pulses.\\[4pt] [1] M.Purvis et al. Nature Photonics \textbf{7}, 796 (2013). [Preview Abstract] |
Thursday, November 19, 2015 10:06AM - 10:18AM |
TO4.00004: First NIF ARC target shot results Hui Chen, P. Di Nicola, M. Hermann, D. Kalantar, D. Martinez, R. Tommasini The commissioning of the Advanced Radiographic Capability (ARC) laser system in the National Ignition Facility (NIF) is currently in progress. ARC laser is designed to ultimately provide eight beamlets with pulse duration adjustable from 1 to 50 ps, and energies up to 1.7 kJ per beamlet. ARC will add critical capability for the NIF facility for creating precision x-ray backlighters needed for many current NIF ICF and HED experiments. ARC can also produce MeV electrons and protons for new science experiment on NIF. In the initial set of experiments, 4 of the 8 beamlets are being commissioned up to 1 kJ per beam at 30 ps pulse length using foil and wire targets. X-ray energy distribution, spot size and pulse duration are measured using various diagnostics. This talk will describe the shot setup and results. [Preview Abstract] |
Thursday, November 19, 2015 10:18AM - 10:30AM |
TO4.00005: Simulation study of enhancing laser-driven multi-keV line-radiation through application of external magnetic fields G. Elijah Kemp, J.D. Colvin, K.B. Fournier, M.J. May, M.A. Barrios, M.V. Patel, J.M. Koning, H.A. Scott, M.M. Marinak Laser-driven, spectrally tailored, high-flux x-ray sources have been developed over the past decade for testing the radiation hardness of materials used in various civilian, space and military applications. The optimal electron temperatures for these x-ray sources occur around twice the desired photon energy. At the National Ignition Facility (NIF) laser, the available energy can produce plasmas with $\sim10\,keV$ electron temperatures which result in highly-efficient $\sim5\,keV$ radiation but less than optimal emission from the $>10\,keV$ sources. In this work, we present a possible venue for enhancing multi-$keV$ x-ray emission on existing laser platforms through the application of an external magnetic field. Preliminary radiation-hydrodynamics calculations with \textsc{Hydra} suggest as much as $2-14\times$ increases in laser-to-x-ray conversion efficiency for $22-68\,keV$ K-shell sources are possible on the NIF laser -- without any changes in laser-drive conditions -- through the application of an external axial $50\,T$ field. [Preview Abstract] |
Thursday, November 19, 2015 10:30AM - 10:42AM |
TO4.00006: Beam-Pointing Designs for Exploding-Pusher Proton and X-Ray Backlighting Targets at the National Ignition Facility R.S. Craxton, Y.Z. Kong, E.M. Garcia, P.Y. Huang, J.P. Kinney, P.W. McKenty, R. Zhang, S. Le Pape, F. Coppari, R.F. Heeter, D.A. Liedahl, B.J. MacGowan, J.R. Rygg, M.B. Schneider, C.K. Li, T.S. Perry The 2-D hydrodynamics code \textit{SAGE},\footnote{R. S. Craxton and R. L. McCrory, J. Appl. Phys. \textbf{56}, 108 (1984).} which includes 3-D laser ray tracing, has been used to design laser pointing configurations for thin-shell, exploding-pusher targets at the National Ignition Facility (NIF) being considered as point sources of protons and continuum x rays. Since it is desired to irradiate these targets using limited numbers of beams, uniformity is maximized by individually pointing the different beams in each quad. An important design constraint is to minimize the laser blow-by into opposing beam ports. Designs have been developed for a variety of planned experiments. A six-quad design was used for the first proton backlighter development shot on the NIF. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Thursday, November 19, 2015 10:42AM - 10:54AM |
TO4.00007: Computational Design of Short Pulse Laser Driven Iron Opacity Experiments Madison E. Martin, Richard A. London, Sedat Goluoglu, Heather D. Whitley Opacity is a critical parameter in the transport of radiation in systems such as inertial confinement fusion capsules and stars. The resolution of current disagreements between solar models and helioseismological observations would benefit from experimental validation of theoretical opacity models. Short pulse lasers can be used to heat targets to higher temperatures and densities than long pulse lasers and pulsed power machines, thus potentially enabling access to emission spectra at conditions relevant to solar models. In order to ensure that the relevant plasma conditions are accessible and that an emission measurement is practical, we use computational design of experiments to optimize the target characteristics and laser conditions. Radiation-hydrodynamic modeling, using HYDRA [1], is used to investigate the effects of modifying laser irradiance, target dimensions, and dopant dilution on the plasma conditions and emission of an iron opacity target. Several optimized designs reaching temperatures and densities relevant to the radiative zone of the sun will be discussed. \\[4pt] [1] M. M. Marinak, et. al. Physics of Plasmas 8, 2275 (2001). [Preview Abstract] |
Thursday, November 19, 2015 10:54AM - 11:06AM |
TO4.00008: Investigating the double-peaked K-shell pulse emitted by the Xe-doped Ar gas-puff shot Z 2603 J.P. Apruzese, J.L. Giuliani, N.D. Ouart, V. Tangri, A.J. Harvey-Thompson, B. Jones, C.A. Jennings A recent series of Ar gas-puff experiments on Sandia National Laboratories' Z generator achieved K-shell yields in excess of 300 kJ. However, when a Xe dopant of 0.8{\%} by number was added to the central jet, the K-shell yield was reduced by a factor of 3, and, only on this shot, it appeared in two distinct, nearly equal peaks. We investigate possible causes of this phenomenon in terms of the evolving properties of the pinch, and the temperature sensitivity of Ar K-shell emissivity. [Preview Abstract] |
Thursday, November 19, 2015 11:06AM - 11:18AM |
TO4.00009: Simulations of Recent Ar Gas Puff Radiation Sources on the ZR Generator Varun Tangri, A.J. Harvey-Thompson, J.W. Thornhill, J.L. Giuliani, N.D. Ouart, B. Jones, C.A. Jennings We present radiation-magnetohydrodynamic simulations of four recent Ar gas puff shots on the refurbished Z generator. The simulations using Mach2-TCRE are calculated in r-z geometry with a tabulated collisional radiative equilibrium model for the non-LTE ionization kinetics and radiation transport. The four shots were designed to study the effects upon the Ar K-shell radiation output due to a change in the initial gas puff distribution. The shots Z2604 and Z2605 had a double shell puff and a central jet. The shots Z2560 and Z2628 did not have a central jet. Calculated yields are close to experimental error-bars. Results will be presented for the impact of the initial gas puff distribution on the K-shell yield. [Preview Abstract] |
Thursday, November 19, 2015 11:18AM - 11:30AM |
TO4.00010: K-shell Radiation Source of a Low Z Puff on a High Z Jet J.L. Giuliani, A. Dasgupta, A.L. Velikovich, R.J. Commisso, V. Tangri, A.J. Harvey-Thompson, D.J. Ampleford, C.A. Jennings We examine a Z-pinch gas puff load wherein the JxB coupled energy from the generator is coupled to the ion thermal and kinetic energy of an outer, imploding low Z pusher. The central jet is the target K-shell emitter of larger Z. At assembly on axis, the kinetic energy of the pusher is dissipated, and during the strong compression, the excess ion thermal energy of the pusher is transferred to the electrons of the jet producing excitation and radiation from the high Z target. An analysis of the dynamics is first presented through a 0-D snowplow model to show that with a centrally peaked initial density profile the kinetic energy of implosion can be half of the total JxB energy [1]. Next we present 2-D Mach2-TCRE simulations for the ZR generator of a Ne puff onto a central Kr jet. The capability of this load design for producing K-shell emission from Kr will be examined. \\[4pt] [1] J.L. Giuliani and R.J. Commisso, ``A Review of the Gas-Puff Z Pinch as an X-Ray and Neutron Source,'' accepted in IEEE Trans. Plasma Sci. June, 2015. [Preview Abstract] |
Thursday, November 19, 2015 11:30AM - 11:42AM |
TO4.00011: K-shell spectroscopy uncertainty due to spectral models Taisuke Nagayama, J.E. Bailey, G. Loisel, G.A. Rochau, S.B. Hansen, C. Blancard, Ph. Cosse, C.A. Iglesias, J. Colgan, C. Fontes, D. Kilcrease, J.J. MacFarlane, I. Golovkin, R. Florido, R.C. Mancini In high energy density plasma physics, K-shell spectra from H-, He-, and Li-like ions are often used to diagnose plasma conditions. Line ratios and line broadening of the measured spectra are sensitive to the electron temperature and density of the source plasma, respectively. Thus, plasma electron temperature, $T_e$, and electron density, $n_e$, can be uniquely and precisely determined by reproducing the measured spectra with a spectral model. However, the different spectral models do not perfectly agree with each other and the diagnostic results depend on the selection of spectral models. Here, we investigate the level of disagreement in inferred $T_e$ and $n_e$ due to differences in spectral models. Models in the study are ABAKO, ATOMIC, FLYCHK, OPAL, OPAS, PrismSPECT, and SCRAM. As an example, we selected Mg K-shell spectroscopy used for Fe opacity experiments [Bailey et al, Nature 517, 56 (2015)] where Fe plasma conditions are inferred from K-shell spectra of a Mg dopant. The $T_e$ and $n_e$ diagnostics using different models agree within 5\% and 30\%. We discuss the main source of discrepancies. [Preview Abstract] |
Thursday, November 19, 2015 11:42AM - 11:54AM |
TO4.00012: X-Ray Spectroscopy of Rapidly Heated Buried-Aluminum Layers C.R. Stillman, P.M. Nilson, C. Mileham, D.D. Meyerhofer, D.H. Froula, M.E. Martin, R.A. London The thermal x-ray emission spectrum from rapidly heated solid targets containing a buried-aluminum layer was measured. The targets were driven by high-contrast 1$\omega $ or 2$\omega $ laser pulses at focused intensities up to $1 \times 10^{19}$ W/cm$^2$. Aluminum thermal lines in the 1.5- to 2-keV spectral range were measured with time-integrated and time-resolved spectrometers. The average plasma conditions in the buried layer were inferred by fitting x-ray spectra from a collisional-radiative atomic physics model to the measured data. The achievement of dense, high-temperature plasma conditions with an intense 2$\omega $ drive will be discussed. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944 and the Stewardship Science Graduate Fellowship Grant Number DE-NA0002135. [Preview Abstract] |
Thursday, November 19, 2015 11:54AM - 12:06PM |
TO4.00013: Measurements of Laser Generated X-ray Spectra from Irradiated Gold Foils Joshua Davis, Paul Keiter, Paul Drake, Sallee Klein Soft x-ray sources may provide a means of driving photoionization fronts in materials with a Z \textgreater 2. To generate these soft x-rays at a traditional UV laser facility, a gold converter foil can be implemented that absorbs the UV photons and heats up to act as a quasi-continuum blackbody emitter with a characteristic temperature of $\sim$ 100eV. However, it takes time for the heating wave to propagate through the foil, with thicker foils having a longer delay before measureable emission is produced. Prior work has studied the emission characteristics of foil x-ray sources but was limited to laser pulses of 1ns or less. Our interest is in long duration sources (\textgreater 1ns) which requires the use of thicker Au foils. To better understand how the increased foil thickness affects emission we have performed experiments at the Omega-60 laser facility studying the x-ray intensity and total emission time of 0.5, 1.0, and 2.0$\mu$m thick gold foils driven by a 2kJ, 6ns laser pulse. This presentation will discuss the results of these experiments and will include a discussion of how these results compare with theoretical predictions. [Preview Abstract] |
Thursday, November 19, 2015 12:06PM - 12:18PM |
TO4.00014: Spectral measurements of asymmetrically-irradiated capsule backlighters Paul Keiter, R. Paul Drake Capsule backlighters provide a quasi-continuum x-ray spectrum over a wide range of photon energies. [Hansen et al, 2008] Typically lasers irradiate the capsule backlighter symmetrically, however, in complex experimental geometries, this is not always possible. In recent experiments we irradiated capsule backlighters asymmetrically and measured the x-ray spectrum from multiple directions. We will present time-integrated spectra over the photon energy range of $\sim$2-13 keV and time-resolved spectra over the photon energy range of $\sim$2-3 keV. We will also discuss the use of these backlighters in future absorption spectroscopy experiments. This work is supported by the U.S. Department of Energy, through the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE-NA0001840, and the National Laser User Facility Program, grant number DE-NA0002032, and through the Laboratory for Laser Energetics, University of Rochester by the NNSA/OICF under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Thursday, November 19, 2015 12:18PM - 12:30PM |
TO4.00015: Evaluating bent x-ray crystal optics with synchrotron radiation Nino Pereira, Albert Macrander To attain optimum performance in applications such as x-ray maging and spectroscopy, a spherically bent crystal must diffract well across its entire surface. X-ray topography of sample crystals shows isolated regions where diffraction is problematic, even for a crystal where inspection with visible light does not suggest problems. Covering problem spots may improve the crystal's focus, and decrease the background. We explore the special properties of synchrotron radiation to examine typical spherical crystals from alpha-quartz, at the 90 deg scattering angle that is especially convenient for sagittal focusing for a spherical optic. [Preview Abstract] |
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