Bulletin of the American Physical Society
58th Annual Meeting of the APS Division of Plasma Physics
Volume 61, Number 18
Monday–Friday, October 31–November 4 2016; San Jose, California
Session PO5: ICF: Integrated Experiments II |
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Chair: Eric Loomis, Los Alamos National Laboratory Room: 230 B |
Wednesday, November 2, 2016 2:00PM - 2:12PM |
PO5.00001: Physics Considerations for Double-Shell Capsules W. Daughton, D.S. Montgomery, D. Wilson, A. Simakov, E. Dodd, L. Merritt, T. Cardenas, J.L. Kline, S. Batha Double-shell capsules offer an alternative approach for achieving burn on the National Ignition Facility. These capsules consist of a low-Z ablatively driven outer shell that converges a factor of $\sim3$ before colliding with a high-Z inner shell filled with liquid DT. Such targets permit short simple laser pulses using near vacuum hohlraum conditions, which have been shown to eliminate laser plasma instabilities, resulting in good coupling efficiency. The adiabat of the fuel is set predominantly by a single strong shock, followed by the nearly adiabatic compression of the fuel volume by a convergence ratio of $\sim9$. In this talk, we present some key physics consideration for double-shell targets, including design constraints for optimizing the kinetic energy transfer to the inner shell. These basics considerations are confirmed by a series of 1D simulations, resulting in several optimized point designs. Two-dimensional simulations are employed to evaluate the influence of low-mode asymmetries, as well as the stability of both the outer and inner shells as the implosion proceeds. [Preview Abstract] |
Wednesday, November 2, 2016 2:12PM - 2:24PM |
PO5.00002: Double Shell Plans and First Results from Outer Shell Keyhole Experiments D.S. Montgomery, E.C. Merritt, W.S. Daughton, E.N. Loomis, D.C. Wilson, E.S. Dodd, J.L. Kline, S.H. Batha, H.F. Robey Double-shells are an alternative approach to achieving indirect drive ignition on NIF. These targets consist of a low-Z ablatively-driven outer shell that impacts a high-Z inner shell filled with DT fuel. In contrast to single-shell designs, double-shell targets burn the fuel via volume ignition, albeit with a lower gain. While double-shell capsules are complicated to fabricate, their design includes several beneficial metrics such as a low convergence pusher (C.R. $<$ 10), low implosion speed (250 km/s), a simple few-ns laser drive in a vacuum hohlraum, less sensitivity to hohlraum asymmetries, and low expected laser-plasma instabilities. We describe plans for developing double shell capsule implosions on NIF, and discuss challenges as well as uncertainties and trade-offs in the physics issues compared to single-shells, such as sensitivity to hard x-ray preheat of the inner shell. First experimental results measuring hard x-ray preheat, shock breakout and shock symmetry from outer-shell experiments using the NIF Keyhole platform will be presented. [Preview Abstract] |
Wednesday, November 2, 2016 2:24PM - 2:36PM |
PO5.00003: NIF Double Shell outer-shell experiments E. C. Merritt, D. S. Montgomery, J. L. Kline, W. S. Daughton, D. C. Wilson, E. S. Dodd, D. B. Renner, T. Cardenas, S. H. Batha At the core of the Double Shell concept is the kinetic energy transfer from the outer shell to the inner shell via collision. This collision sets both the implosion shape of the inner shell, from imprinting of the shape of the outer shell, as well as the maximum energy available to compress the DT fuel. Therefore, it is crucial to be able to control the time-dependent shape of the outer shell, such that the outer shell is nominally round at the collision time. We present the experiment results from our sub-scale (\textasciitilde 1 MJ) NIF outer-shell only shape tuning campaign, where we vary shape by changing a turn-on time delay between the same pulse shape on the inner and outer cone beams. This type of shape tuning is unique to this platform and only possible since the Double Shell design uses a single-shock drive (4.5 ns reverse ramp pulse). The outer-shell only targets used a 5.75 mm diameter standard near-vacuum NIF hohlraum with 0.032 mg/cc He gas fill, and a Be capsule with 0.4{\%} uniform Cu dopant, with \textasciitilde 242 um thick ablator. We also present results from a third outer-shell only shot used to measure shell trajectory, which is critical in determining the shell impact time. [Preview Abstract] |
Wednesday, November 2, 2016 2:36PM - 2:48PM |
PO5.00004: Initial results from the DSPlanar experiments on OMEGA E.S. Dodd, E.C. Merritt, D.S. Montgomery, W. Daughton, D.W. Schmidt, T. Cardenas, D.C. Wilson, S.H. Batha Recently, LANL has begun a project aimed ultimately at fielding a neutron-producing double-shell capsule at the National Ignition Facility (NIF). Initial experiments have begun at both the NIF and OMEGA laser facilities over the last year. At OMEGA, halfraum-driven planar targets will be used to study physics issues important to double shell implosions, but outside of a convergent geometry. In particular, side-on radiography through a tube has advantages over imaging through the hohlraum and double-shell capsule at NIF. We plan to study a number physics issues with this platform, including both 1-d and higher dimensional effects. In 1-d, momentum transfer from the ablator to the inner shell, and the effect of pre-heat on the inner shell can be studied. Higher dimensional effects, in the form of hydrodynamic instabilities, can also be studied. Pre-heat expansion of the inner shell can lead to an unstable interface, which can be mitigated by a tamper layer. Manufacturing tolerances can be used to mitigate against feature-driven instability growth, such as from a glue joint or fill tube. Initial results on the amount pre-heat from various ablator materials will be given, along with a discussion of future plans. [Preview Abstract] |
Wednesday, November 2, 2016 2:48PM - 3:00PM |
PO5.00005: Low Convergence path to Fusion I: Ignition physics and high margin design Kim Molvig, M.J. Schmitt, G.H. McCall, R. Betti, D.H. Foula, E.M. Campbell A new class of inertial fusion capsules is presented that combines multi-shell targets with laser direct drive at low intensity (280 TW/cm$^{\mathrm{2}})$ to achieve robust ignition. These Revolver targets [K. Molvig, et. al., \textit{Phys. Rev. Letters,} \textbf{116}, 255003 (2016)] consist of three concentric metal shells, enclosing a volume of 10s of \textmu g of liquid deuterium-tritium fuel. The inner shell pusher, nominally of gold, is compressed to over 2000 g/cc, effectively trapping the radiation and enabling ignition at low temperature ( 2.5 keV) and relatively low implosion velocity (20 cm/micro-sec) at a fuel convergence of 9. Ignition is designed to occur well "upstream" from stagnation, with implosion velocity at 90{\%} of maximum, so that any deceleration phase mix will occur only after ignition. Mix, in all its non-predictable manifestations, will effect net yield in a Revolver target -- but not the achievement of ignition and robust burn. Simplicity of the physics is the dominant principle. There is no high gain requirement. These basic physics elements can be combined into a simple analytic model that generates a complete target design specification given the fuel mass and the kinetic energy needed in the middle (drive) shell (of order 80 kJ). This research supported by the US DOE/NNSA, performed in part at LANL, operated by LANS LLC under contract DE-AC52-06NA25396. [Preview Abstract] |
Wednesday, November 2, 2016 3:00PM - 3:12PM |
PO5.00006: Low convergence path to fusion II: An integrated NIF design. Mark J. Schmitt, K. Molvig, G. H. McCall, D. H. Edgel, J. E. Myatt, R. Betti, D.H. Froula, E. M. Campbell We report on the Revolver design methodology for achieving ignition using large diameter (6mm) Be shells to efficiently (\textasciitilde 10{\%}) convert laser energy from a short, \textasciitilde 5 ns, 320TW laser pulse on the National Ignition Facility (NIF) into a dynamic pressure source for inertial confinement fusion. It is shown that this source can be used to kinetically drive two nested internal shells to achieve ignition conditions inside a central liquid DT core. Using principles recently elucidated [K. Molvig, et. al, Phys Rev Lett 116 255003, 2016], we formulate a robust optimization of a triple shell target that mitigates long-standing issues with conventional ignition schemes including drive non-uniformities, laser plasma instabilities (including the hot electrons they produce), non-local heat conduction and deceleration Rayleigh-Taylor (RT) mix. Rad-hydro simulations predict ignition initiating at 2.5keV with 90{\%} of the maximum inner shell velocity remaining (before deceleration RT can cause significant mix in the compressed DT fuel). Simulations in 2D show that the short pulse design produces a spatially uniform kinetic drive that is tolerant to random 5{\%} variations in laser cone power. Moreover, it will be shown that intra-shell parameters can be adjusted to mitigate convergence growth of capsule spatial non-uniformities. This research supported by the US DOE/NNSA, performed in part at LANL, operated by LANS LLC under contract DE-AC52-06NA25396. [Preview Abstract] |
Wednesday, November 2, 2016 3:12PM - 3:24PM |
PO5.00007: ABSTRACT WITHDRAWN |
Wednesday, November 2, 2016 3:24PM - 3:36PM |
PO5.00008: The 1-D Campaign on OMEGA: A Systematic Approach to Find the Optimum Path to Ignition R. Betti, A. Bose, A.R. Christopherson, E.M. Campbell, T.J.B. Collins, J.P. Knauer, A.V. Maximov, P.B. Radha, S.P. Regan, W. Shang, C. Stoeckll A methodology is devised to make progress toward achieving ignition starting from a well{\-}understood implosion. This technique uses several metrics that rely on trends in experimental observables rather than absolute values and their agreement with simulations. The flexibility of the OMEGA laser makes it ideal to implement such a platform. For direct-drive inertial fusion, this methodology is being implemented starting from high-adiabat, low-convergence implosions of DT cryogenic capsules. The first implosions of this campaign use single-parameter scans to determine trends in the experimental observables used to identify degradation mechanisms affecting implosion performance. In this implosion, short-wavelength perturbations or hot-electron preheat are turned on and off by using (a) laser smoothing on/off keeping identical laser pulse shapes and (b) low/high intensities keeping the shock timing fixed. Another pair of shots with identical laser pulse shapes but different payloads (DT and CH) is used to characterize the preheat level. The first results of this systematic approach are presented. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944 [Preview Abstract] |
Wednesday, November 2, 2016 3:36PM - 3:48PM |
PO5.00009: Multidimensional Study of High-Adiabat OMEGA Cryogenic Experiments T.J.B. Collins, R. Betti, A. Bose, A.R. Christopherson, J.P. Knauer, J.A. Marozas, A.V. Maximov, A. Mora, P.B. Radha, W. Shang, A. Shvydky, C. Stoeckl, K.M. Woo, G. Varchas Despite recent advances in modeling laser direct-drive inertial confinement fusion (ICF) experiments, there remains a predictability gap. This is particularly shown by the shortfall in hot-spot pressures inferred from OMEGA cryogenic implosions. To address this, a series of high-adiabat, cryogenic implosions were performed on OMEGA. These shots were performed with and without single-beam smoothing by spectral dispersion, at low and high drive intensities. These shots represent a regime where good agreement with simulation is expected because of the high adiabat. Multidimensional simulations of these shots will be presented with an emphasis on comparison with experimental indicators of departure from spherical symmetry (``1-D-ness''). The roles of short- and long-wavelength perturbations are~considered. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, November 2, 2016 3:48PM - 4:00PM |
PO5.00010: Wetted Foam Liquid DT Layer ICF Experiments at the NIF R. E. Olson, R. J. Leeper, R. R. Peterson, S. A. Yi, A. B. Zylstra, J. L. Kline, P. A. Bradley, L. Yin, D. C. Wilson, B. M. Haines, S. H. Batha A key physics issue in indirect-drive ICF relates to the understanding of the limitations on hot spot convergence ratio (CR), principally set by the hohlraum drive symmetry, the capsule mounting hardware (the ``tent''), and the capsule fill tube. An additional key physics issue relates to the complex process by which a hot spot must be dynamically formed from the inner ice surface in a DT ice-layer implosion. These physics issues have helped to motivate the development of a new liquid DT layer wetted foam platform$^{\mathrm{1}}$ at the NIF that provides an ability to form the hot spot from DT vapor and experimentally study and understand hot spot formation at a variety of CR's in the range of 12\textless CR\textless 25. Flexibility in CR will provide a means for exploring variations in the partitioning of available energy between the hot spot and the low adiabat cold fuel during the stagnation process and can allow for a fundamentally different (and potentially more robust) process of hot spot formation$^{\mathrm{2}}$. This new experimental platform is currently being used in a series of experiments to discover a range of CR's at which DT layered implosions will have understandable performance -- providing a sound basis from which to determine the requirements for ICF ignition. $^{\mathrm{1}}$R. E. Olson \textit{et al}., J. Phys. Conf. Ser. \textbf{717}, 012042 (2016). $^{\mathrm{2}}$R. E. Olson and R. J. Leeper, Phys. Plasmas \textbf{20}, 092705 (2013). [Preview Abstract] |
Wednesday, November 2, 2016 4:00PM - 4:12PM |
PO5.00011: Modeling of low convergence liquid layer wetted foam implosions at the National Ignition Facility S. A. Yi, R. E. Olson, L. Yin, D. C. Wilson, H. W. Herrmann, A. B. Zylstra, B. M. Haines, R. R. Peterson, P. A. Bradley, R. C. Shah, J. L. Kline, R. J. Leeper, S. H. Batha, J. L. Milovich, L. F. Berzak Hopkins, D. D. Ho, N. B. Meezan A new platform has been developed that allows for lower convergence ratio implosions ($\mathrm{CR}\sim 15$) than is possible with traditional DT ice layered capsules ($\mathrm{CR}\sim 30$). We present HYDRA simulation models of the first low convergence DT implosions on NIF utilizing the wetted foam platform. When tuned to match the observed bangtime and hotspot symmetry, our rad-hydro models agree well with many experimental observables. In particular, the inferred hotspot density and pressure are consistent with simulations, and our modeled burn widths are in better relative agreement with the data than in high convergence implosions. The observed neutron yields are approximately 60-70\% of postshot calculations. These results indicate that at a reduced convergence ratio $\mathrm{CR}\sim 15$ the hotspot formation process is well modeled by our simulations. [Preview Abstract] |
Wednesday, November 2, 2016 4:12PM - 4:24PM |
PO5.00012: Analysis Of Wetted-Foam ICF Capsule Perormance $^{\mathrm{\mathbf{1}}}$ R. Peterson, R. Olson, A. Zylstra, B. Haines, A. Yi, P. Bradley, L. Yin, R. Leeper, J. Kline The performance of wetted-foam ICF capsules is investigated with the RAGE Eulerian radiation-hydrodynamics computer code. We are developing an experimental platform on NIF that employs a wetted foam liquid DT fuel layer ICF capsules.$^{\mathrm{2,3}}$ By varying the capsule temperature, the vapor density in the capsule can be prescribed, and the hot spot convergence ratio (CR) of the capsule implosion can be controlled. This allows us to investigate the fidelity of RAGE in modeling of capsule implosions as the value of CR is varied. In the NIF experiments, CR can be varied from 12 to 25. This presentation will cover simulations with RAGE of three NIF shots performed in 2016; a DD and a DT liquid fuel shot with CR$=$14 and a DT shot with CR$=$16. It will also discuss analysis of future experiments. $^{\mathrm{1}}$This work was performed under auspices of the U. S. DOE by LANL. $^{\mathrm{2}}$ R.E. Olson, et al., J. Phys. Conf. Ser., \underline {\textbf{717}}, 012042 (2016). $^{\mathrm{3\thinspace }}$R.E. Olson and R. J. Leeper, Phys. Plasmas \underline {\textbf{20}}, 092705 (2013). [Preview Abstract] |
Wednesday, November 2, 2016 4:24PM - 4:36PM |
PO5.00013: First liquid-layer implosion experiments on the National Ignition Facility Alex Zylstra, R Olson, R Leeper, J Kline, S.A. Yi, R. Peterson, P. Bradley, B. Haines, L. Yin, D. Wilson, H. Herrmann, R. Shah, J. Biener, T. Braun, B. Kozioziemski, L. Berzak Hopkins, A. Hamza, A. Nikroo, N. Meezan, M. Biener, J. Sater, C. Walters Replacing the standard ice layer in an ignition design with a liquid layer allows fielding the target with a higher central vapor pressure, leading to reduced implosion convergence ratio (CR). At lower CR, the implosions are expected to be more robust to instabilities and asymmetries than standard ignition designs. The first liquid-layer implosions on the National Ignition Facility (NIF) have been performed by wicking the liquid fuel into a supporting foam. A 3-shot series has been conducted at CR=14-16 using a HDC ablator driven by a 3-shock pulse in a near-vacuum Au hohlraum; data and inferred quantities, such as pressure, show good agreement with expectations. [Preview Abstract] |
Wednesday, November 2, 2016 4:36PM - 4:48PM |
PO5.00014: Using ensembles of simulations to find high-fidelity post-shot models of inertial confinement implosions at the National Ignition Facility Ryan Nora, John E. Field, Brian Spears, Cliff A. Thomas The inertial confinement fusion program at the National Ignition Facility is performing subscale experiments for a variety of implosion designs. Successful designs, those with experiments that are similar to postshot simulation, will be fielded at larger scale. This work supports the program's effort by establishing high fidelity post-shot simulations matching all experimental observables: scalar data, such as the neutron yield and areal densities; vector data, such as flange nuclear activation diagnostics; and image data, such as time-dependent x-ray self-emission images. We will present a metric for measuring the nearness of postshot simulations to experiments. In particular, we will emphasize area-based (as opposed to contour-based) image analysis metrics (e.g., Zernike moments) for comparison of x-ray self-emission images. The postshot metrics and methodology will be applied to the Big Foot implosion design as an example. [Preview Abstract] |
Wednesday, November 2, 2016 4:48PM - 5:00PM |
PO5.00015: Suppression of RTI by the use of high-Z doping scheme on mega-joule scale implosion Takashi Shiroto, Naofumi Ohnishi, Atsushi Sunahara, Shinsuke Fujioka, Akira Sasaki Rayleigh—Taylor Instability (RTI) is one of the most critical issue to prevent thermonuclear ignition of Inertial Confinement Fusion (ICF). High-Z doping scheme (S. Fujioka et al., Phys. Rev. Lett. 92, 195001, 2004) seems to be a candidate for suppression of the RTI, but there is a report that pure mid-Z ablators have no capability to improve the implosion symmetry for ignition-scale target designs (M. Lafon et al., Phys. Plasmas 22, 032703, 2015). We used 0.05\%-doped brominated polystyrene (CHBr) for the rad-hydro numerical experiment, whose opacity tables were validated by a planar target experiment. It was numerically demonstrated that perturbation growth was suppressed at relatively high mode even in the ignition-relevant scale. The ablative-RTI was NOT suppressed at the main-drive phase when the pulse intensity became the maximum as mentioned in the Lafon’s past work. However, the high-Z doping scheme was valid at the foot-drive phase when the intensity was $\leq 10^{14}\ \mathrm{W/cm^2}$, which is consistent with the Fujioka’s experiment. Resultant areal density with the CHBr ablator was twice as high as the pure plastic one. This fact implies the significance of hydrodynamic instabilities at relatively-low acceleration, such as the foot pulse of Kidder-like implosion. [Preview Abstract] |
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