Bulletin of the American Physical Society
59th Annual Meeting of the APS Division of Plasma Physics
Volume 62, Number 12
Monday–Friday, October 23–27, 2017; Milwaukee, Wisconsin
Session TI2: Direct Drive, Fast Ignition, and Kinetic Modeling |
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Chair: John Kline, Los Alamos National Laboratory Room: 102ABC |
Thursday, October 26, 2017 9:30AM - 10:00AM |
TI2.00001: The One-Dimensional Cryogenic Implosion Campaign on OMEGA: Modeling, Experiments, and a Statistical Approach to Predict and Understand Direct-Drive Implosions* Invited Speaker: R. Betti The 1-D campaign on OMEGA is aimed at validating a novel approach to design cryogenic implosion experiments and provide valuable data to improve the accuracy of 1-D physics models. This new design methodology is being tested first on low-convergence, high-adiabat ($\alpha \sim 6$~to~7) implosions and will subsequently be applied to implosions with increasing convergence up to the level required for a hydro-equivalent demonstration of ignition. This design procedure assumes that the hydrodynamic codes used in implosion designs lack the necessary physics and that measurements of implosion properties are imperfect. It also assumes that while the measurements may have significant systematic errors, the shot-to-shot variations are small and that cryogenic implosion data are reproducible as observed on OMEGA. One of the goals of the 1-D campaign is to find a mapping of the data to the code results and use the mapping relations to design future implosions. In the 1-D campaign, this predictive methodology was used to design eight implosions using a simple two-shock pulse design, leading to pre-shot predictions of yields within 5{\%} and ion temperatures within 4{\%} of the experimental values. These implosions have also produced the highest neutron yield of $\sim 10^{14}$ in OMEGA cryogenic implosion experiments with an areal density of $\sim $100~mg/cm$^{\mathrm{2}}$. Furthermore, the results from this campaign have been used to test the validity of the 1-D physics models used in the radiation--hydrodynamics codes. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE{\-}NA0001944 and LLNL under Contract DE-AC52-07NA27344. * In collaboration with J.P. Knauer, V. Gopalaswamy, D. Patel, K.M. Woo, K.S. Anderson, A. Bose, A.R. Christopherson, V.Yu. Glebov, F.J. Marshall, S.P. Regan, P.B. Radha, C. Stoeckl, and E.M. Campbell. [Preview Abstract] |
Thursday, October 26, 2017 10:00AM - 10:30AM |
TI2.00002: Wavelength Detuning Cross-Beam Energy Transfer Mitigation Scheme for Direct-Drive: Modeling and Evidence from National Ignition Facility Implosions Invited Speaker: J.A. Marozas Cross-beam energy transfer (CBET) has been shown to significantly reduce the laser absorption and implosion speed in direct-drive implosion experiments on OMEGA and the National Ignition Facility (NIF). Mitigating CBET assists in achieving ignition-relevant hot-spot pressures in deuterium--tritium cryogenic OMEGA implosions. In addition, reducing CBET permits lower, more hydrodynamically stable, in-flight aspect ratio ignition designs with smaller nonuniformity growth during the acceleration phase. Detuning the wavelengths of the crossing beams is one of several techniques under investigation at the University of Rochester to mitigate CBET. This talk will describe these techniques with an emphasis on wavelength detuning. Recent experiments designed and predicted using multidimensional hydrodynamic simulations including CBET on the NIF have exploited the wavelength arrangement of the NIF beam geometry to demonstrate CBET mitigation through wavelength detuning in polar-direct-drive (PDD) implosions.\footnote{J. A. Marozas \textit{et al.}, ``First Observation of Cross-Beam Energy Transfer Mitigation for Direct-Drive Inertial Confinement Fusion Implosions Using Wavelength Detuning at the National Ignition Facility,'' submitted to Physical Review Letters.} Shapes and trajectories inferred from time-resolved x-ray radiography of the imploding shell, scattered-light spectra, and hard x-ray spectra generated by suprathermal electrons all indicate a reduction in CBET. These results and their implications for direct-drive ignition will be presented and discussed. In addition, hydrodynamically scaled ignition-relevant designs for OMEGA implosions exploiting wavelength detuning will be presented. Changes required to the OMEGA laser to permit wavelength detuning will be discussed. Future plans for PDD on the NIF including more-uniform implosions with CBET mitigation will be explored. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Thursday, October 26, 2017 10:30AM - 11:00AM |
TI2.00003: Demonstration of Efficient Core Heating of Magnetized Fast Ignition in FIREX project Invited Speaker: Tomoyuki Johzaki Extensive theoretical and experimental research in the FIREX–I project over the past decade revealed that the large angular divergence of the laser generated electron beam is one of the most critical problems inhibiting efficient core heating in electron-driven fast ignition\footnote{S.Fujioka, et al., Phys Rev. E \textbf{91}, 063102 (2015).}. To solve this problem, beam guiding using externally applied kilo-tesla class magnetic field was proposed, and its feasibility has recently been numerically demonstrated\footnote{T. Johzaki, et al., Plasma Phys. Control. Fusion \textbf{59}, 014045 (2017).}. In 2016, integrated experiments at ILE Osaka University demonstrated core heating efficiencies reaching $>$ 5 \% and heated core temperatures of 1.7 keV. In these experiments, a kilo-tesla class magnetic field was applied to a cone-attached Cu(II) oleate spherical solid target by using a laser-driven capacitor-coil. The target was then imploded by G-XII laser and heated by the PW-class LFEX laser. The heating efficiency was evaluated by measuring the number of Cu-K-$\alpha$ photons emitted. The heated core temperature was estimated by the X-ray intensity ratio of Cu Li-like and He-like emission lines. To understand the detailed dynamics of the core heating process, we carried out integrated simulations using the FI$^{3}$ code system. Effects of magnetic fields on the implosion and electron beam transport, detailed core heating dynamics, and the resultant heating efficiency and core temperature will be presented. I will also discuss the prospect for an ignition-scale design of magnetized fast ignition using a solid ball target. [Preview Abstract] |
Thursday, October 26, 2017 11:00AM - 11:30AM |
TI2.00004: Exploring the dynamics of kinetic/multi-ion effects and ion-electron equilibration rates in ICF plasmas at OMEGA Invited Speaker: H. Sio During the last few years, an increasing number of experiments have shown that kinetic and multi-ion-fluid effects do impact the performance of an ICF implosion. Observations include: increasing yield degradation as the implosion becomes more kinetic; thermal decoupling between ion species; anomalous yield scaling for different fuel mixtures; ion diffusion; and fuel stratification. The common theme in these experiments is that the results are based on time-integrated nuclear observables that are affected by an accumulation of effects throughout the implosion, which complicate interpretation of the data. A natural extension of these studies is therefore to conduct time-resolved measurements of multiple nuclear-burn histories to explore the dynamics of kinetic/multi-ion effects in the fuel and their impact on the implosion performance. This was accomplished through simultaneous, high-precision measurements of the relative timing of the onset, bang time and duration of DD, D$^{\mathrm{3}}$He, DT and T$^{\mathrm{3}}$He burn from T$^{\mathrm{3}}$He (with trace D) or D$^{\mathrm{3}}$He gas-filled implosions using the new Particle X-ray Temporal Diagnostic (PXTD) on OMEGA. As the different reactions have different temperature sensitivities, $T_{i}(t)$ was determined from the data. Uniquely to the PXTD, several x-ray emission histories (in different energy bands) were also measured, from which a spatially averaged $T_{e}(t)$ was also determined. The inferred $T_{i}(t)$ and $T_{e}(t)$ data have been used to experimentally explore ion-electron equilibration rates and the Coulomb Logarithm for various plasma conditions. Finally, the implementation and use of PXTD, which represents a significant advance at OMEGA, have laid the foundation for implementing a $T_{e}(t)$ measurement in support of the main cryogenic DT programs at OMEGA and the NIF. This work was supported in part by the US DOE, LLE, LLNL, and DOE NNSA SSGF. [Preview Abstract] |
Thursday, October 26, 2017 11:30AM - 12:00PM |
TI2.00005: Understanding Yield Anomalies in ICF Implosions via Fully Kinetic Simulations Invited Speaker: William Taitano In the quest towards ICF ignition, plasma kinetic effects are among prime candidates for explaining some significant discrepancies between experimental observations and rad-hydro simulations. To assess their importance, high-fidelity fully kinetic simulations of ICF capsule implosions are needed. Owing to the extremely multi-scale nature of the problem, kinetic codes have to overcome nontrivial numerical and algorithmic challenges, and very few options are currently available. Here, we present resolutions of some long-standing yield discrepancy conundrums using a novel, LANL-developed, 1D-2V Vlasov-Fokker-Planck code iFP. iFP possesses an unprecedented fidelity and features fully implicit time-stepping, exact mass, momentum, and energy conservation, and optimal grid adaptation in phase space, all of which are critically important for ensuring long-time numerical accuracy of the implosion simulations. Specifically, we concentrate on several anomalous yield degradation instances observed in Omega campaigns, with the so-called “Rygg effect” [1], or an anomalous yield scaling with the fuel composition, being a prime example. Understanding the physical mechanisms responsible for such degradations in non-ignition-grade Omega experiments is of great interest, as such experiments are often used for platform and diagnostic development, which are then used in ignition-grade experiments on NIF. In the case of Rygg’s experiments, effects of a kinetic stratification of fuel ions on the yield have been previously proposed as the anomaly explanation, studied with a kinetic code FPION, and found unimportant. We have revisited this issue with iFP and obtained excellent yield-over-clean agreement with the original Rygg results, and several subsequent experiments. This validates iFP and confirms that the kinetic fuel stratification is indeed at the root of the observed yield degradation. \newline [1] J.R. Rygg et al., Phys. Plasmas, 13, 052702 (2006). [Preview Abstract] |
Thursday, October 26, 2017 12:00PM - 12:30PM |
TI2.00006: Measurements of ion species separation in strong plasma shocks Invited Speaker: Hans Rinderknecht Shocks are important dynamic phenomena in inertial confinement fusion (ICF) and astrophysical plasmas. While the relationship between upstream and downstream plasmas far from the shock front is fully determined by conservation equations, the structure of shock fronts is determined by dynamic kinetic processes. Kinetic theory and simulations predict that the width of a strong (M \textgreater 2) collisional plasma shock front is on the order of tens of ion mean-free-paths. The shock front structure plays an important role for overall dynamics when the shock front width approaches plasma scale lengths, as in the spherically converging shock in the DT-vapor in an ICF implosion. However, there has been no experimental data benchmarking shock front structure in the plasma phase. The structure of a shock front in a plasma with multiple ion species has been directly measured for the first time using a combination of Thomson scattering and proton radiography in experiments on the OMEGA laser. Thomson scattering of a 263.25 nm probe beam is used to diagnose electron density, electron and ion temperature, ion species concentration, and flow velocity in strong shocks (M \textasciitilde 5) propagating through low-density ($\rho $ \textasciitilde 0.1 mg/cc) plasmas composed of H(98{\%})$+$Ne(2{\%}). Within the shock front, velocity separation of the ion species is observed for the first time: the light species (H) accelerates to of order the shocked fluid velocity (450 microns/ns) before the heavy species (Ne) begins to move. This velocity-space separation implies that the separation of ion species occurs at the shock front, a predicted feature of shocks in multi-species plasmas but never observed experimentally until now. Comparison of experimental data with PIC, Vlasov-Fokker-Planck, and multi-component hydrodynamic simulations will be presented. [Preview Abstract] |
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