Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Plasma Physics
Volume 57, Number 12
Monday–Friday, October 29–November 2 2012; Providence, Rhode Island
Session CO4: Hohlraum and X-ray Physics |
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Chair: Daniel Clark, Lawrence Livermore National Laboratory Room: 551AB |
Monday, October 29, 2012 2:00PM - 2:12PM |
CO4.00001: Post-Shot Simulations of NIC Experiments with Comparison to X-ray Measurements David Eder, Oggie Jones, Larry Suter, Alastair Moore, Marilyn Schneider National Ignition Campaign experiments at NIF are ongoing and post-shot simulations play an important role in understanding the physical processes occurring in the quest for demonstrating fusion burn. In particular, it is important to understand the x-ray environment inside the hohlraum targets, which is studied using various x-ray diagnostics. The Dante instrument measures the time dependent x-ray emission escaping out of the hohlraum laser entrance holes (LEHs) and the SXI instrument provides a time-integrated image of both soft and hard x-rays. We compare calculated total x-ray emission with Dante data as well as the relative high energy Mband emission that contributes to capsule preheat. We correct our calculated x-ray emission to account for differences between simulation and data on LEH closure using SXI data. We provide results for both ``standard candle'' simulation with no added multipliers and for simulations with time-dependent multipliers that are used to obtain agreement with shock timing and implosion velocity data. The physics justification for the use of multipliers is to account for potential missing energy or incorrect ablation modeling. The relative importance of these two effects can be studied through comparison of post-shot simulations with x-ray measurements. [Preview Abstract] |
Monday, October 29, 2012 2:12PM - 2:24PM |
CO4.00002: ABSTRACT WITHDRAWN |
Monday, October 29, 2012 2:24PM - 2:36PM |
CO4.00003: HYDRA DCA Atomic Kinetics and Applications to Modeling NIF Hohlraums Mehul V. Patel, Howard A. Scott, Michael M. Marinak Modeling of NLTE atomic kinetics is playing an increasingly important role in simulations of NIF targets. NLTE kinetics is required for modeling emissions from high-Z hohlraum wall materials, and may also be necessary for accurate modeling of capsule ablators. The 2D/3D ICF radiation hydrodynamics code HYDRA offers two in-line atomic kinetics packages: average-atom based XSN, and Detailed Configuration Accounting (DCA). Recent updates to the HYDRA DCA package have integrated higher accuracy atomic physics into simulations of NIF hohlraums while increasing the computational efficiency of the package. We will review how our NLTE modeling of hohlraums has evolved and assess the sensitivity of integrated simulation results (such as the bang time and hohlraum radiation temperature) to modeling parameters. [Preview Abstract] |
Monday, October 29, 2012 2:36PM - 2:48PM |
CO4.00004: Capsule Implosion Symmetry in NIF Hohlraums R.P.J. Town, P.A. Michel, L. Divol, D.A. Callahan, O.S. Jones, J. Milovich, M.D. Rosen, J.D. Moody, L.R. Benedetti, D.K. Bradley, S. Glenn, N. Izumi, S.F. Khan, A.E. Pak, V.A. Smalyuk, R. Tommasini, D.S. Bailey, J.A. Harte, G.B. Zimmerman, G.A. Kyrala, R. Scott A key requirement for the achievement of ignition on the National Ignition Facility (NIF) is to adequately control the hotspot low mode shape. This is diagnosed by measuring the X-ray self-emission from the imploding capsule, either in surrogate symmetry capsule, or in layered implosions. The primary method of controlling the equatorial drive symmetry is to vary the power balance between the inner and outer cones either directly or by crossbeam energy transfer. Varying the power balance within the inner cones controls the azimuthal asymmetry. This paper will review the status of the low-mode shape of layered implosions and compare to integrated simulations using a new backscatter model and in-line crossbeam power transfer model. [Preview Abstract] |
Monday, October 29, 2012 2:48PM - 3:00PM |
CO4.00005: 3-D Simulations of NIF Target Implosions Jose Milovich, Ogden Jones, Richard Town, David Bradley To achieve ignition on the National Ignition Facility (NIF), a cryogenic capsule must be imploded with minimal low mode asymmetries. The NIF was designed with a large number of beams arranged to azimuthally cover the hohlraum wall thereby minimizing asymmetries in this direction. This high degree of regularity has allowed the use of 2-D radiation-hydrodynamics codes to model the behavior of ignition targets. However, there are some target features whose effects are not captured in 2-D simulations and thus require a full 3-D approach. The most important are the starburst, a pattern of four azimuthal cut-outs in the hohlraum wall use to characterize the uniformity of the ice layer, and a single diamond-covered diagnostic hole required to image the equatorial symmetry. To assess their influence on implosion performance we have performed 3D radiation-hydrodynamic simulations and found that they have a non-negligible effect on the shape of the hot spot. We will discuss our results and show how these findings have motivated a redesign of the NIF targets to mitigate their effects. [Preview Abstract] |
Monday, October 29, 2012 3:00PM - 3:12PM |
CO4.00006: Advances in NIF Shock Timing Experiments Harry Robey Experiments are underway to tune the shock timing of capsule implosions on the National Ignition Facility (NIF). These experiments use a modified cryogenic hohlraum geometry designed to precisely match the performance of ignition hohlraums. The targets employ a re-entrant Au cone to provide optical access to multiple shocks as they propagate in the liquid deuterium-filled capsule interior. The strength and timing of all four shocks is diagnosed with VISAR (Velocity Interferometer System for Any Reflector). Experiments are now routinely conducted in a mirrored keyhole geometry, which allows for simultaneous diagnosis of the shock timing at both the hohlraum pole and equator. Further modifications are being made to improve the surrogacy to ignition hohlraums by replacing the standard liquid deuterium (D2) capsule fill with a deuterium-tritium (DT) ice layer. These experiments will remove any possible surrogacy difference between D2 and DT as well as incorporate the physics of shock release from the ice layer, which is absent in current experiments. Experimental results and comparisons with numerical simulation are presented. [Preview Abstract] |
Monday, October 29, 2012 3:12PM - 3:24PM |
CO4.00007: Experimental investigation of hohlraum energetics in ignition targets S.A. MacLaren, J.H. Hammer, H.-S. Park, M.B. Schneider, P.M. Celliers, D.A. Callahan, D.E. Hinkel, M.L. Kervin, B.R. Maddox, R.E. Marrs, R.P. Town, K. Widmann, M.J. Wilson, B.E. Yoxall In indirect-drive inertial fusion, x-ray drive generated in the hohlraum is transported and coupled to the ablator, generating the hydrodynamic drive that implodes the capsule. This combination of transport and coupling determines the implosion velocity, which must be sufficiently high to heat the deuterium-tritium (DT) ``hot spot'' to fusion temperatures as well as strongly compress the surrounding cold DT fuel. To date, implosion velocities of ignition capsules measured at the National Ignition Facility (NIF) have been consistently lower than those predicted by baseline simulations. Two new types of NIF experiments have been carried out to investigate this discrepancy. These experiments seek to separate the effects of x-ray transport within the hohlraum from the ignition capsule ablator's response to the drive. Results of these experiments are compared with simulation. [Preview Abstract] |
Monday, October 29, 2012 3:24PM - 3:36PM |
CO4.00008: Radiation Transport through cylindrical foams with heated walls Kevin Baker, Steve MacLaren, Joshua Kallman, Ken Heinz, Warren Hsing Radiation transport through low density SiO2 foams has been experimentally studied on the Omega laser. In particular these experiments examined the effects on radiation transport when the boundaries of the SiO2 foam are heated such that energy loss to the boundaries is minimized. The initial density of the SiO2 foams was determined by taking an x-ray radiograph of the foams using a monochromatic Henke source at multiple x-ray energies. The radiation drive used to both study the transport in the SiO2 foam as well as to heat the higher density CRF wall was generated in a laser-heated gold hohlraum using $\sim $7.5 kJ of the laser energy. The time-dependent spatial profile of the heat wave breaking out of the SiO2 foam was detected with an x-ray streak camera coupled with a soft x-ray transmission grating. The Omega DANTE diagnostic measured the radiation drive in the hohlraum and the Omega VISAR diagnostic monitored the spatial temperature gradient in the foam section of the hohlraum. [Preview Abstract] |
Monday, October 29, 2012 3:36PM - 3:48PM |
CO4.00009: KULL Simulations of OMEGA Radiation Flow Experiments J. Kallman, S. MacLaren, K. Baker, P. Amala, K. Lewis, M. Zika The problem of radiation flow in a right circular cylinder is of interest for the verification and validation of radiation codes, which utilize several mechanisms for determining radiation transport (diffusion, discrete ordinates, and Monte Carlo). This flow is analogous to free molecular flow in a similar geometry.\footnote{E. Garelis and T.E. Wainwright. Phys. Fluids. \textbf{16}, 4 (1973)} A series of experiments were conducted on the OMEGA laser in cases with a low-density heated cylindrical wall. The experiments consisted of a 1.6 mm diameter gold hohlraum containing an on-axis 700 $\mu $m diameter SiO$_2$ cylinder contained in an 80 $\mu$m thick carbon foam tube. Five shots panning three test cases were used: the nominal geometry described above (heated wall), the carbon tube replaced with solid gold, and a gold cap placed on the laser end of the cylinder assembly to block axial radiation flow. Simulations of each experimental target type were run with the KULL radiation code, and were used to compare the different radiation transport packages in KULL by employing synthetic diagnostics to match the experimental DANTE cavity radiation temperature time history and soft x-ray images taken by a streak camera imaging the far end of the hohlraum. [Preview Abstract] |
Monday, October 29, 2012 3:48PM - 4:00PM |
CO4.00010: Supersonic Radiation Transport Experiments using large-scale Hohlraums on the NIF Alastair Moore, T. Guymer, J. Morton, M. Stevenson, M. Taccetti, N. Lanier, J. Kline, R. Peterson, K. Mussack, B. Devolder, J. Workman The National Ignition Facility (NIF) has made possible the exploration of fundamental radiation hydrodynamics in hitherto inaccessible regimes. Diffusive supersonic x-radiation transport, in which the radiative energy flux ($\sigma $T$^{4})$ exceeds that of the material energy ($\varepsilon \rho $cs) producing a radiation-driven heat front that travels faster than the material sounds speed, is one such case. The understanding of such phenomena is of wide interest across a range of radiation-hydrodynamics.To study such phenomena, we have developed a high-temperature $\sim $350eV hohlraum platform that can, for the first-time, drive a supersonic radiative diffusion or Marshak wave through in excess of 50-100 cold material optical depths of 120mg/cc Si aerogel or chlorinated CH foam -- approx. 10 mean free paths when heated to 200eV. To constrain radiation hydrodynamics models we measure the emitted radiation using multiple x-ray power and imaging diagnostics and in particular the structure of the soft x-ray thermal emission spectrum. We describe the hohlraum platform development and methodology to constrain the opacity and equation of state of the foam materials, together with initial measurements of the radiation transport demonstrating the diffusive and supersonic nature. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Monday, October 29, 2012 4:00PM - 4:12PM |
CO4.00011: 2D-simulation Design of An Ignition Hohlraum Xin Li, Changshu Wu, Yiqing Zhao, Shiyang Zou, Wudi Zheng Based on two-dimensinal (2D) calculations, this article describes the method by which we can design an ignition hohlraum under the conditions of capsule drive and laser energy and power limit. We use JC Code (3T Version) to simulate the coupling between laser and hohlraum and use the improved post code to obtain the x-ray drive on capsule. The study focuses onsome key problems, which do not appear in the 0D design. These problems include how to choose hohlraum gas fill density and capsule drive pulse length, how to describe the main pulse temporal behavior of laser drive, and how to tune the P2 drive asymmetry on capsule in the main pulse to zero. Laser plasma interaction (LPI) is not considered in the study because of the lack of analysis ability. But we leave sufficient margin for it. The final ignition hohlraum 2D design requires 1.4 MJ and 416 TW of laser energy and peak power, to achieve a drive temperature of 300 eV with 14{\%} M-band photon (hv$>$2keV) ratio in an cylindrical target and gives a yield of about 16 MJ. The ratio of the outer beam energy over the inner beam energy is 3. About 85{\%} laser energy converts to x-rays. [Preview Abstract] |
Monday, October 29, 2012 4:12PM - 4:24PM |
CO4.00012: The simulation studyof foam Au as hohlraum wall in indirect-drive inertial confinement fusion Changshu Wu, Wenbing Pei, Shaoping Zhu The high Zmetallic foam ashohlraum wall ca reduce hydrodynamic losses, and hence, net absorbed energy (``wall loss''). Therefore, his approach is used to increase hohlraum couplingefficiency in laser indirect drive inertial-confinement fusion (ICF). We have alsosimulated the foam Au as hohlraum wall with our on-dimensional (1D radiation hydrodynamic code RDMG andtwo-dimensional (2D radiation hydrodynamic code LARED-H. he required radiation drive for capsule implosionis more complex pulse shape, and it has been used to ablate thenormal density Au wall. The simulationresult indicates thekinetic energy fraction is only about 18\%, and it is less than that with constant radiation drive. The wall loss is difficult to be reduced by reduced kinetic energy with decreased originaldensity of Au wall, and the wall loss increases in lower density region because of the increased internal energy. Although the wall loss can't be reduced, the 1D simulation result by RDMG indicates that the kinetic energy and theblowoff mass decreasewith decreasedoriginaldensity of Au wall. The 2D simulationresult by LARED-Hindicates that reducedhydrodynamic motion can restrain the motion of laser spots, and that is ofbenefit to the symmetry control. [Preview Abstract] |
Monday, October 29, 2012 4:24PM - 4:36PM |
CO4.00013: Determining the hohlraum radiation temperature and$ M$-band fraction by using shock wave technique on SGIII-prototype laser facility Wenyi Huo, Ke Lan, Yongsheng Li, Dong Yang, Sanwei Li Experiments have been conducted on SGIII-prototype laser facility using tow materials Al and Ti as shock wave witness plates. The radiation temperature $^{\mbox{TR}}$ and M-band fraction fM inside a hohlraum are determined by using the observed shock velocities in Al and Ti. This is the first experimental demonstration of the proposal that $^{\mbox{TR}}$ and fM can be simultaneously determined by using shock wave technique [Y. S. Li, \textit{et a}l., Phys. Plasmas \textbf{18}, 022701 (2011)]. For the Au hohlraum used in the experiments, TR is about 160 eV and $^{\mbox{fM}}$ is around 4.3\% under a 1 ns laser pulse of 2 kJ. The results from this technique are complementary to those from the broadband soft x-ray spectrometer (SXS), and the technique can be used to determine $^{\mbox{TR}}$ and fM inside an ignition hohlraum. [Preview Abstract] |
Monday, October 29, 2012 4:36PM - 4:48PM |
CO4.00014: ABSTRACT WITHDRAWN |
Monday, October 29, 2012 4:48PM - 5:00PM |
CO4.00015: To acquire more detailed radiation drive by use of ``quasi-steady'' approximation in atomic kinetics Guoli Ren, Wenbing Pei, Ke Lan, Peijun Gu, Xin Li In current routine 2D simulation of hohlraum physics, we adopt the principal-quantum- number(n-level) average atom model(AAM) in NLTE plasma description. However, the detailed experimental frequency-dependant radiative drive differs from our n-level simulated drive, which reminds us the need of a more detailed atomic kinetics description. The orbital-quantum- number(nl-level) average atom model is a natural consideration, however the nl-level in-line calculation needs much more computational resource. By distinguishing the rapid bound-bound atomic processes from the relative slow bound-free atomic processes, we found a method to build up a more detailed bound electron distribution(nl-level even nlm-level) using in-line n-level calculated plasma conditions(temperature, density, and average ionization degree). We name this method ``quasi-steady approximation'' in atomic kinetics. Using this method, we re-build the nl-level bound electron distribution (P$_{nl})$, and acquire a new hohlraum radiative drive by post-processing. Comparison with the n-level post-processed hohlraum drive shows that we get an almost identical radiation flux but with more fine frequency-denpending spectrum structure which appears only in nl-level transition with same n number(n=0) . [Preview Abstract] |
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