Bulletin of the American Physical Society
49th Annual Meeting of the Division of Plasma Physics
Volume 52, Number 11
Monday–Friday, November 12–16, 2007; Orlando, Florida
Session CO5: Compression and Burn I |
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Chair: Radha Bahukutumbi, University of Rochester Room: Rosen Centre Hotel Salon 11/12 |
Monday, November 12, 2007 2:00PM - 2:12PM |
CO5.00001: Measurable Lawson Criterium and Hydro-Equivalent Curves for Inertial Confinement Fusion R. Betti, C.D. Zhou The Lawson's criterion that determines the onset of thermonuclear ignition is usually expressed through the product \textit{p$\tau $} $\approx $ 10 atm s, where $p$ is the plasma pressure and \textit{$\tau $} is the energy confinement time. In magnetic fusion devices, both the pressure and confinement time are routinely measured, and the performance of each discharge can be assessed by comparing the value of \textit{p$\tau $} with respect to the ignition value (10 atm s). In inertial fusion, both $p$ and \textit{$\tau $} cannot be directly measured and the performance of a subignited ICF implosion cannot be assessed with respect to the ignition condition. Here, we derive a form of the Lawson's criterion that can be directly measured in ICF implosions. Such a new ignition criterion depends on the only two measurable quantities in the ICF fuel assembly: the total areal density and the hot-spot ion temperature. In cryogenic implosions, the total areal density can be measured through secondary proton spectroscopy, neutron spectroscopy, or x-ray radiography. The ion temperature is measured with the neutron time-of-flight (nTOF) diagnostic. Thus, one can use such a new criterion to assess how far current and future subignited ICF implosions are from achieving ignition. This work was supported by the U.S. Department of Energy under Cooperative Agreements DE-FC52-92SF19460 and DE-FC02-04ER54789. [Preview Abstract] |
Monday, November 12, 2007 2:12PM - 2:24PM |
CO5.00002: Implosion experiments using D$_{2}\backslash ^{3}$He filled glass capsules doped with noble gases: A Study. John Benage, George Kyrala, Doug Wilson, Mark Gunderson, Hanna Makaruk, Johann Frenje, C.K. Li, Richard Petrasso, Baruch Yaakobi, Warren Garbett When simulations are unable to match the yield in ICF implosion experiments, ``mix'' is commonly used to fix the simulation. If this fix is in any way assumed to model reality, then we are assuming that the simulations calculate the effect of the mix on the implosion and yield correctly. To study whether this assumption is valid, we have done a series of experiments that purposely add a fixed amount of mix of varying atomic number and density. The experiments are very well characterized, measuring the proton and neutron yields, the ion and electron temperatures, the $\rho $R and radius of the capsule, the radiation emission, and the x-ray spectra from the capsule. We find that,in general, the calculations have great difficulty matching this data. A summary of the measurements for various dopants and dopant levels and how well the calculations compare will be presented. Some possible reasons for the modeling difficulties will be discussed along with some preliminary efforts to address these problems. [Preview Abstract] |
Monday, November 12, 2007 2:24PM - 2:36PM |
CO5.00003: Radiative Effects on Direct Drive Implosion Temperatures J.A. Koch, H.-K. Chung, R. Heeter, W. Hsing, R.W. Lee, A. Miles, H.-S. Park, H. Robey, H. Scott, R. Tommasini, J. Frenje, C.K. Li, R. Petrasso, V. Glebov We have performed experiments at the Omega Laser Facility to measure time-resolved electron (Te) and ion temperature (Ti) in implosion plasmas. These experiments used direct laser drive on thin glass shells filled with a mixture of D, $^{3}$He, Kr, and Xe, and used neutron and proton emission to diagnose Ti along with x-ray emission to diagnose Te. The Kr dopant serves as an optically-thin tracer for Te measurements via K-shell spectroscopy, while the Xe dopant enhances radiation losses and alters time-dependent temperatures through the shock and compression phases. These experiments are intended to establish an experimental platform for studying the energetics effects of high-Z dopants in hot, dense plasmas, including ignition plasmas at the National Ignition Facility. We describe the experiments and the supporting hydrodynamics simulations. [Preview Abstract] |
Monday, November 12, 2007 2:36PM - 2:48PM |
CO5.00004: Modeling NLTE effects in thin-shell direct-drive Omega capsule implosions A.R. Miles, J.A. Koch, W. Hsing, H.-S. Park, H.F. Robey, H.A. Scott, J.A. Frenje, C.K. Li, R.D. Petrasso, F.H. Seguin, V.Yu. Glebov, C. Stoeckl An experimental effort is currently underway in which thin (4 $\mu $m) glass-shell DHe3-filled capsules are fielded in direct-drive implosions at the OMEGA Laser Facility. The thin shells result in fast implosions and shock-heating of the gas to ion temperatures up to about 10 keV, while the electron and radiation temperatures remain significantly lower and separate from one another. One goal of these experiments is to obtain independent time-resolved measurements of these three temperatures in order to study matter-radiation coupling in a system that is nonequilibrium and can be made to be NLTE by adding high-Z dopants such as Xe. The addition of Xe has a strong imact on the implosion dynamics and TN yields, and makes the targets much more difficult to model via numerical simulations. In this paper, we compare simulation results obtained with different NLTE models and discuss requirements for reasonable agreement with the data. [Preview Abstract] |
Monday, November 12, 2007 2:48PM - 3:00PM |
CO5.00005: Effects of $^{3}$He Addition on Implosion of DT Capsules on Omega H.W. Herrmann, J.M. Mack, D.C. Wilson, J.R. Langenbrunner, C.S. Young, J.H. Cooley, S.C. Evans, T.J. Sedillo, G.A. Kyrala, L. Welser-Sherrill, C.J. Horsfield, D.W. Drew, E.K. Miller, V. Yu Glebov Glass (SiGDP) capsules were imploded in direct drive on the Omega laser to look for anomalous degradation in yield (i.e., beyond what is predicted) with $^{3}$He addition similar to the ``factor of two'' degradation previously reported by MIT at a 50{\%} $^{3}$He atom fraction (Rygg \textit{et al,. }Phys. Plasmas 13, 2006). We did not see a significant anomalous degradation. The cause of the ``Rygg'' anomaly is as of yet unexplained, but differences in gas mixture (DT vs D$_{2})$ or shell parameters (glass vs plastic, diameter and wall thickness) may be responsible for the absence of this anomaly in the recent data. In addition, a short laser pulse (600 ps) was used to temporally separate shock and compression yield components in order to investigate mix. Previously, anomalously low compression yield had been observed when imploding glass targets containing 10 atm DT with 10 kJ of laser energy. This effect was not seen in the recent data with 5 atm DT and 15 kJ, and the resulting $\gamma $ and $n$ burn histories were in good qualitative agreement with predictions for $^{3}$He addition. Work supported by US DOE/NNSA, performed by LANL, operated by LANS LLC under Contract DE-AC52-06NA25396. [Preview Abstract] |
Monday, November 12, 2007 3:00PM - 3:12PM |
CO5.00006: Mix Degradation in DT Filled Capsules When Shock and Compression Yields are Resolved D.C. Wilson, H.W. Herrmann, J.M. Mack, C.S. Young, G.A. Kyrala, J.H. Cooley, L. Welser-Sherrill, J.R. Langenbrunner, S.C. Evans, T.J. Sedillo, C.J. Horsfield, D.W. Drew, E.K. Miller, V. Yu. Glebov 1100$\mu $m dia. DT(5atm) + 3He (0,1,or 5 atm) filled glass capsules were directly driven on the Omega laser to measure yield, X-ray images, and especially the burn time history. The 600ps square pulse increases time separation between the ``shock'' yield (before the reflected shock reaches the incoming shell) and later ``compression'' yield. Matching the timing and amount of this early ``shock'' yield in the implosions fixes the electron conduction flux limiter. The Scannapieco and Cheng mix model results are compared with measured yield, burn temperatures and histories, and gated X-ray images. The experiment shows degradation of both the shock and compression yield, but relatively more degradation of the compression yield than explained by the model. The first gated images, which occur when the reflected shock reaches the incoming shell, show significant mixing has already occurred. But the lack of X-ray emission 60ps earlier suggests no mixing then. Work supported by US DOE/NNSA, performed by LANL, operated by LANS LLC under Contract DE-AC52-06NA25396. LA-UR-07-4929. [Preview Abstract] |
Monday, November 12, 2007 3:12PM - 3:24PM |
CO5.00007: Evaluation and modeling of burn reaction histories using a directly driven capsule with two laser pulses J.H. Cooley, L. Welser-Sherrill, D.C. Wilson, H.W. Herrmann, J.M. Mack, S.C. Evans, T.J. Sedillo, C.S. Young, C.J. Horsfield, D.W. Drew, E.K. Miller, V. Yu. Glebov, C. Stoekl, R.A. Lerche Experiments were designed and fielded on the Omega laser to measure reaction history from capsules exposed to two distinct 600ps laser pulses. The purpose of the experiments was to produce a burn history with two peaks by using a time delay between the two laser pulses and thus obtain a compression and re-compression yield. However, although the results obtained produced two distinct yield peaks, further modeling indicated that the dynamics of the shell and in particular the mix of the ablator into the fuel were very different then our earlier understanding. These results and analysis will be presented and discussed. Work supported by US DOE/NNSA, performed by LANL, operated by LANS LLC under Contract DE-AC52-06NA25396. [Preview Abstract] |
Monday, November 12, 2007 3:24PM - 3:36PM |
CO5.00008: Development of Shock-Timing Techniques for the National Ignition Facility T.R. Boehly, M.A. Barrios, D.E. Fratanduono, T.C. Sangster, D.D. Meyerhofer, P.M. Celliers, D. Munro, G.W. Collins, O.L. Landen, R.E. Olson To optimize the drive for ignition targets on the National Ignition Facility, initial experiments will use surrogate targets to measure the timing and strength of shocks produced by that drive. These targets use an ignition-style capsule fitted with a deuterium-filled re-entrant cone embedded in that shell. The shocks are observed in flight through a transparent window using optical diagnostics. We report on OMEGA experiments that are scaled and designed to validate this shock-timing technique using both open geometry and hohlraum targets with embedded cones, by quantifying and mitigating the effects of preheat by hard-x-ray hohlraum emission on the inner capsule surface, deuterium column, and window. This work was supported by U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-92SF19460. [Preview Abstract] |
Monday, November 12, 2007 3:36PM - 3:48PM |
CO5.00009: X-Ray Ablation Rates of ICF Capsule Materials R.E. Olson, G.A. Rochau, R.J. Leeper Accurate knowledge of the X-ray ablation rates of low-Z capsule materials will be essential for successful indirect-drive ICF ignition experiments. We have performed experiments to measure the X-ray ablation rates in Be, Cu-doped Be, high density carbon (HDC), polystyrene (CH), Ge-doped CH, and polyimide. The X-ray fluxes were supplied by hohlraums driven by the Omega Laser at the University of Rochester [1]. The measurements were made in planar geometry utilizing diagnostic techniques described in Ref. 2. Be and Cu-doped Be have been selected as the ablator materials to be used in ignition capsules at U.S. National Ignition Facility (NIF). HDC has been selected as a NIF backup ablator. The ablation rates in Be and Cu-doped Be are in the range of 3-12 mg/cm$^{2}$/ns for hohlraum radiation temperatures of 160-250 eV. The HDC ablation rates are a bit lower, in the range of 2-9 mg/cm$^{2}$/ns for temperatures of 170-260 eV. The corresponding implied ablation pressures are in the range of 40-160 Mbar for beryllium and 20-140 Mbar for HDC. Our post-shot computational simulations are mostly within the uncertainties of the ablation rate measurements. An iterative rocket model has been developed and used to relate the planar ablation rate data to convergent Omega ablation rate experiments and also to full-scale NIF ignition capsule calculations. [1] T. R. Boehly et al., Opt. Commun. \underline {133}, 496 (1997). [2] R. E. Olson et al., Phys. Plasmas \underline {11}, 2778 (2004). [Preview Abstract] |
Monday, November 12, 2007 3:48PM - 4:00PM |
CO5.00010: Time-resolved measurements of in-flight ablator performance using streaked x-ray radiography Damien Hicks, Brian Spears, Chuck Sorce, Peter Celliers, Otto Landen, Gilbert Collins, Thomas Boehly Determining ablator performance during an implosion is a critical part of the NIF tuning campaign. In particular, it is vital to have an accurate, in-flight measure of the velocity, areal density, and mass of the ablator. We present a new technique which achieves time-resolved measurements of all these parameters in a single, area-backlit, streaked radiograph. This is accomplished by tomographically inverting the radiograph to determine the radial density profile at each time step; scalar quantities such as the average position, thickness, areal density, and mass of the ablator can then be determined simply by taking moments of this density profile. Application of this technique is demonstrated on Cu-doped Be capsule implosions at Omega. This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48. [Preview Abstract] |
Monday, November 12, 2007 4:00PM - 4:12PM |
CO5.00011: Influence and measurement of mass ablation in ICF implosions Brian Spears, D. Hicks, C. Velsko, M. Stoyer, H. Robey, D. Munro, S. Haan, O. Landen, D. Wilson, A. Nikroo Point design ignition capsules designed for the National Ignition Facility use an xray-driven Be(Cu) ablator to compress the DT fuel. Ignition specifications require the mass of unablated Be(Cu), called residual mass, be known to within 1{\%} of the initial ablator mass when the fuel reaches peak velocity. We discuss the impact of variations in residual mass on the relevant capsule failure modes based on one- and two-dimensional radiation hydrodynamics. Experiments designed to measure and to tune the amount of residual mass are being developed as part of the National Ignition Campaign. We also discuss a set of measurement techniques that aim to measure the residual mass along with the peak velocity of the DT fuel. UCRL-ABS-232765 [Preview Abstract] |
Monday, November 12, 2007 4:12PM - 4:24PM |
CO5.00012: Monoenergetic Proton Radiography Studies of Matter and Field Distributions in Cone-in-Shell Capsule Implosions J.R. Rygg, F.H. Seguin, C.K. Li, J.A. Frenje, R.D. Petrasso, R. Betti, D.D. Meyerhofer, C. Stoekl, W. Theobald The matter and electromagnetic (E/B) field distributions in inertial confinement fusion implosions have been studied for the first time using monoenergetic proton radiography. Time-gated observations of the deflection and downshift of 14.7-MeV D$^{3}$He protons passing through implosions of cone-in-shell capsules were used to measure megagauss magnetic fields with complex topology in the capsule corona, areal densities in the capsule, and substantial blowoff of cone material. This work was supported by the Univ. of Rochester Fusion Science Center (Contract 412761-G). [Preview Abstract] |
Monday, November 12, 2007 4:24PM - 4:36PM |
CO5.00013: Monoenergetic Proton Radiography Observations of E and B Field Evolution Outside Imploding, Direct-Drive ICF Capsules F.H. Seguin, C.K. Li, J.R. Rygg, J.A. Frenje, R.D. Petrasso, R. Betti, O.V. Gotchev, J.P. Knauer, F.J. Marshall, D.D. Meyerhofer, V.A. Smalyuk Monoenergetic proton radiography has been used to make the first observations of electromagnetic fields that appear outside imploding inertial confinement fusion capsules as a result of laser-plasma interactions in direct-drive experiments at OMEGA. Images made with 15-MeV protons and $\sim $130 ps time resolution show that field structures that are roughly spherically symmetric form around the capsule shortly after the onset of laser illumination; these gradually change to radially filamented structures before dying away. Estimates of mode numbers and field strengths will be made, and the relationship between the field evolution and measured spectra of ablator ions will be discussed. 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 FSC at Univ. Rochester. [Preview Abstract] |
Monday, November 12, 2007 4:36PM - 4:48PM |
CO5.00014: Monoenergetic Proton Radiography Measurements of Implosion Dynamics in Direct-Drive Inertial Confinement Fusion C.K. Li, F.H. Seguin, J.R. Rygg, J.A. Frenje, R.D. Petrasso, V.A. Smalyuk, R. Betti, J. Delettrez, J.P. Knauer, F.J. Marshall, D.D. Meyerhofer, D. Shvarts, R.P.J. Town, O.L. Landen Time-gated, monoenergetic proton radiography provides unique measurements of implosion dynamics of spherical capsules in direct-drive inertial confinement fusion. Proton radiographs obtained at different times, from acceleration through coasting, deceleration, and final stagnation, display a complete picture of ICF spherical implosion. Critical information inferred directly from such images uniquely characterizes the spatial structure and temporal evolution of plasma areal density and field distributions in an imploded target that was hitherto unavailable from conventional measurements. Data are contrasted with both self-emitted x rays and hydro simulations. The work described here was performed in part at the LLE National Laser User's Facility (NLUF), and was supported in part by US DOE, LLNL, LLE and FSC at the Univ. Rochester. [Preview Abstract] |
Monday, November 12, 2007 4:48PM - 5:00PM |
CO5.00015: Double-shell capsules, an alternative to the single-shell cryogenic NIF design G.R. Magelssen, N.D. Delamater, M.A. Gunderson, I.L. Tregillis, M.J. Schmitt Recently, Los Alamos has renewed its effort[1] to design and evaluate double-shell capsules as an alternative to the single- shell cryogenic NIF design.[2] The recent work by Livermore is being used as a starting point.[3-4] One to two megajoules of laser energy is used as input into the designs being considered. Sensitivity studies to P2 and P4 radiation flux asymmetries have been done and are presented in a separate talk.[5] Also, mix calculations of both the NIF capsule design and the double-shell design recently fielded on Omega3 will be presented in another talk.[6] Fully integrated calculations of the double-shell designs will be presented. Preliminary simulations with Rage, an Eulerian AMR code, will be shown that address the issue associated with gaps created by bringing two hemispheres together to create the outer shell. 1. M.S. Varnum et al., Phys. Rev. Lett. 84, 5153 (2000). 2. D.A. Callahan et al., Phys. of Plasmas 13, 56307 (2005). 3. P.A. Amendt et al., Phys. Rev. Lett. 94, 65004 (2005); private communication. 4. J.L. Milovich et al., Phys. of Plasmas 11, 1552 (2004). 5. I.L. Tregillis, this conference. 6. N.D. Delamater et al., this conference. \newline *Work supported by US DOE/NNSA, performed at LANL, operated by LANS LLC under Contract DE-AC52-06NA25396. [Preview Abstract] |
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