Bulletin of the American Physical Society
50th Annual Meeting of the Division of Plasma Physics
Volume 53, Number 14
Monday–Friday, November 17–21, 2008; Dallas, Texas
Session BI1: Inertial Confinement Fusion |
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Chair: Douglas Wilson, Los Alamos National Laboratory Room: Landmark A |
Monday, November 17, 2008 9:45AM - 10:15AM |
BI1.00001: Developing an optimal ignition hohlraum for the National Ignition Facility (NIF) Invited Speaker: Over the past two and a half years a multi-disciplinary team of target physicists, laser scientists, laser engineers and target fabricators have been intensively working together in a process to develop the optimal hohlraum for the first NIF ignition experiments to be performed in 2010-11. This multi-disciplinary organization was essential due to the many and diverse trade-offs that must be made. The trade-offs include ignition capsule drive and symmetry requirements, laser plasma interactions, laser performance, target fabrication and shot rate. In a facility as large as NIF, production schedules must also be included in the optimization process. The work of this team has evaluated candidate ignition hohlraums operating at 270, 285 and 300eV. Capsules evaluated include ones with Be and CH ablators. In this talk we will detail the hohlraum+capsule designs and their physics scaling and sensitivities. This includes the required pulse shapes; meeting the implosion symmetry requirement; sensitivity of hohlraum drive and symmetry to spot size; bulk plasma conditions inside these hohlraums and resulting estimates of laser plasma interaction (LPI) risk. These LPI assessments include both gain based estimates as well as more advanced estimates with the wave based code pf3d and it's derivative, SLIP. Finally, we describe the resulting point design that has been chosen for ignition experiments in 2010-11. [Preview Abstract] |
Monday, November 17, 2008 10:15AM - 10:45AM |
BI1.00002: Time-resolved Measurements of ICF Capsule Ablator Properties by Streaked X-Ray Radiography Invited Speaker: Determining the capsule ablator thickness and peak laser or x-ray drive pressure required to optimize fuel compression is a critical part of ensuring ICF ignition on the NIF. If too little ablator is burned off, the implosion velocity will be too low for adequate final compression; if too much ablator is burned off, the fuel will be preheated or the shell will be broken up by growth of hydrodynamic instabilities, again compromising compression. Avoiding such failure modes requires having an accurate, in-flight measure of the implosion velocity, areal density, and remaining mass of the ablator near peak velocity. We present a new technique which achieves simultaneous time-resolved measurements of all these parameters in a single, area-backlit, x-ray streaked radiograph. This is accomplished by tomographic inversion of the radiograph to determine the radial density profile at each time step; scalar quantities such as the average position, areal density, and mass of the ablator can then be calculated by taking moments of this density profile. Details of the successful demonstration of this technique using backlit Cu-doped Be capsule implosions at the Omega facility will be presented. This work was performed under the auspices of the U.S.Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and in collaboration with Brian Spears, David Braun, Peter Celliers, Gilbert Collins, and Otto Landen at LLNL and Rick Olson at SNL. [Preview Abstract] |
Monday, November 17, 2008 10:45AM - 11:15AM |
BI1.00003: Effects of $^{3}$He Addition on Implosion of DT Capsules on OMEGA Invited Speaker: Glass capsules were imploded in direct drive on the OMEGA laser to look for anomalous degradation in DT yield (i.e., beyond what is predicted) and changes in reaction history with $^{3}$He addition. Similar discrepancies had previously been reported for D/$^{3}$He plasmas, but had not yet been investigated for DT/$^{3}$He. Anomalies such as these provide fertile ground for furthering our physics understanding of ICF implosions. A relatively short laser pulse (600 ps) was used to provide some degree of temporal separation between shock and compression yield components for analysis. Anomalous degradation in the compression component of yield was observed, consistent with the ``factor of two'' degradation previously reported by MIT at a 50{\%} 3He atom fraction in D2 [Rygg et al., Phys. Plasmas 13, 052702 (2006)]. However, clean calculations (assuming no fuel-shell mix) predict the shock component of yield quite well, contrary to the result reported by MIT, but consistent with LANL results in D$_{2}$/$^{3}$He [Wilson, \textit{et al.}, Jrnl Phys: Conf Series 112, 022015 (2008)]. X-ray imaging suggests poor compression of capsules containing $^{3}$He. Leading candidate explanations are poorly understood Equation-of-State (EOS) for gas mixtures, and nonthermal equilibrium between ions and electrons resulting in varying particle pressure with increasing $^{3}$He addition. Results from upcoming experiments in which the D to T ratio will be varied as 3He is added in order to maintain hydro-equivalency will be also be reported on. Hydro-equivalency will allow better shot-to-shot comparisons rather than having to rely on shot-to-code, thus mitigating the effects of code uncertainties. [Preview Abstract] |
Monday, November 17, 2008 11:15AM - 11:45AM |
BI1.00004: Core temperature and density profile measurements for inertial confinement fusion Invited Speaker: An experimental investigation was performed to study the hot spot temperature and density spatial profiles of inertial confinement fusion implosion cores. The experiments at OMEGA employ deuterium-filled plastic shells which include a tracer amount of argon for spectroscopic diagnostics. At the collapse of the implosion argon K-shell line emission is recorded with three identical, gated (50ps) multi-monochromatic x-ray imagers (MMI) that view the core along three quasi-orthogonal lines of sight thus diagnosing the implosion core with an unprecedented level of detail. The MMI instruments use an array of pinholes and a flat multilayer mirror to provide unique multi-spectral core images distributed over a wide spectral range. Core images are obtained for several argon K-shell line transitions. In addition, a titanium doped tracer layer embedded in the plastic shell and located close to the core-shell boundary is used to image simultaneously in absorption the cold dense shell surrounding the core. The data analysis uses detailed atomic kinetics, Stark-broadened line shapes and radiation transport. Several analysis methods have been developed to analyze the data including quasi-analytic, and search and reconstruction based on a novel application of genetic algorithms to plasma spectroscopy. The analysis yields the time-history of the temperature and density profiles of the core, and the spatial extension of mixing. We also discuss time- and spatially-resolved argon line spectra recorded in implosions at Z with slit spectrometers and their application to core structure determination. These measurements and analysis are critical for understanding the plasma dynamics associated with the implosion process and benchmarking hydrodynamic models of high energy density plasmas. [Preview Abstract] |
Monday, November 17, 2008 11:45AM - 12:15PM |
BI1.00005: Proton Radiography of Electromagnetic Fields Associated with Imploded ICF capsules and Laser-Irradiated Hohlraums* Invited Speaker: Time-gated, mono-energetic-proton radiography provides unique measurements of electric (E) and magnetic (B) fields in laser-produced plasmas of imploded ICF capsules and in laser-irradiated hohlraums. These experiments resulted in the first observations of several new and important features previously unrealized [1-5]: first, the observation of radial electric fields inside the imploding capsule that are initially directed inward (at $\sim $10$^{9 }$V/m), reversing direction ($\sim $10$^{8 }$V/m) near deceleration onset, and are likely related to the evolution of the electron pressure gradient; second, the observation of many radial filaments with complex electromagnetic field striations and bifurcations, permeating the entire field of view, and third, the observation of electric fields up to $\sim $ 10$^{9 }$V/m in laser-irradiated gold hohlraums. In addition, these experiments also provide critical information about plasma areal density, both in direct-drive spherical or cone-in-shell targets, during the different times from acceleration, through coasting, deceleration, to final stagnation, thereby providing a comprehensive picture of ICF capsule implosion dynamics. [1] C. K. Li \textit{et al.,} Phys. Rev. Lett. \underline {97}, 135003 (2006), [2] C. K. Li \textit{et al.,} Phys. Rev. Lett. \underline {99}, 015001 (2007). [3] C. K. Li \textit{et al.,} Phys. Rev. Lett. \underline {99}, 055001 (2007). [4] J. R. Rygg \textit{et al., }Science \underline {319}, 1223 (2008). [5] C. K. Li \textit{et al.,} Phys. Rev. Lett. \underline {100} 225001 (2008). \newline \newline *This work was performed in part at the LLE National Laser User's Facility (NLUF), and was supported in part by US DOE, LLNL, LLE, and the Fusion Science Center at Univ. Rochester. \newline \newline **In collaboration with F. H. S\'{e}guin, J. A. Frenje, M. Manuel, D. Casey, N. Sinenian, and R. D. Petrasso (MIT), R. Betti, J. Delettrez, J. P. Knauer, F. Marshall, D. D. Meyerhofer, T. Sangster, D. Shvarts, V. A. Smalyuk, J. A. Soures, and C. Stoeckl (LLE), P. A. Amendt, J. R. Rygg, R. P. J. Town, and O. L. Landen (LLNL), A. Nikroo, C. A. Back, and J. D. Kilkenny (GA). [Preview Abstract] |
Monday, November 17, 2008 12:15PM - 12:45PM |
BI1.00006: Cryogenic Target Performance on OMEGA Invited Speaker: Ignition-relevant target physics is studied using direct-drive cryogenic D$_{2}$ and DT implosions on the OMEGA Laser System. These experiments are designed to validate the performance of polar-drive ignition designs for the NIF using energy-scaled symmetric-drive designs on OMEGA. The focus of current experiments is on shell stability and preheat at ignition adiabats. Recent work with cryogenic cone-in-shell targets demonstrated the sensitivity of the baseline design to shock (mis)-timing and subsequent shock-induced preheating. Hot-electron preheat was shown to be mitigated by including high-$Z$ dopants in the ablator that raise the temperature of the corona and increase the threshold for the two-plasmon decay. Nonlocal heat transport was found to be important in modeling laser absorption during the leading picket, and hydrodynamic growth of target modulations was experimentally shown to be stabilized at peak drive intensities by these nonlocal effects. Finally, much work has been done to prepare the cryogenic target systems for backlighting using the new high-energy, short-pulse beams provided by the recently completed OMEGA EP Facility. This work includes proof-of-principle demonstrations using OMEGA beams to backlight a cryogenic core. The status of short-pulse backlighting will be presented along with the latest fuel compression and target-performance results. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. Contributors: R. Betti, R.S. Craxton, J.A. Delettrez, D.H. Edgell, V.Yu. Glebov, V.N. Goncharov, D.R. Harding, S.X. Hu, J.P. Knauer, F.J. Marshall, R.L. McCrory, P.W. McKenty, D.D. Meyerhofer, P.B. Radha, S.P. Regan, T.C. Sangster, W. Seka, R.W. Short, S. Skupsky, J.M. Soures, C. Stoeckl, B. Yaakobi, UR/LLE; J.A. Frenje, C.K. Li, R.D. Petrasso, F.H. S\'{e}guin, PSFC MIT. [Preview Abstract] |
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