The effect of shock dynamics on compressibility of ignition-scale National Ignition Facility implosions

Zylstra, A. B. [Plasma Science and Fusion Center, Massachusetts Institute of
            Technology, Cambridge, Massachusetts 02139, USA]; Frenje, J. A. [Plasma Science and Fusion Center, Massachusetts Institute of
            Technology, Cambridge, Massachusetts 02139, USA] (ORCID:0000000168460378); Séguin, F. H. [Plasma Science and Fusion Center, Massachusetts Institute of
            Technology, Cambridge, Massachusetts 02139, USA]; Hicks, D. G. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Dewald, E. L. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Robey, H. F. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Rygg, J. R. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Meezan, N. B. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Rosenberg, M. J. [Plasma Science and Fusion Center, Massachusetts Institute of
            Technology, Cambridge, Massachusetts 02139, USA]; Rinderknecht, H. G. [Plasma Science and Fusion Center, Massachusetts Institute of
            Technology, Cambridge, Massachusetts 02139, USA]; Friedrich, S. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Bionta, R. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Olson, R. [Sandia National Laboratory, Albuquerque, New
          Mexico 87185, USA; Los Alamos National Laboratory, Los Alamos, New
          Mexico 87545, USA]; Atherton, J. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Barrios, M. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Bell, P. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Benedetti, R. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Berzak Hopkins, L. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA] (ORCID:0000000291875667); Betti, R. [Laboratory for Laser Energetics, University of
            Rochester, Rochester, New York 14623, USA]; Bradley, D. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Callahan, D. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA] (ORCID:0000000315498916); Casey, D. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Collins, G. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Dixit, S. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Döppner, T. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Edgell, D. [Laboratory for Laser Energetics, University of
            Rochester, Rochester, New York 14623, USA]; Edwards, M. J. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Gatu Johnson, M. [Plasma Science and Fusion Center, Massachusetts Institute of
            Technology, Cambridge, Massachusetts 02139, USA]; Glenn, S. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Glenzer, S. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Grim, G. [Los Alamos National Laboratory, Los Alamos, New
          Mexico 87545, USA]; Hatchett, S. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Jones, O. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Khan, S. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Kilkenny, J. [General Atomics, San Diego, California 92186,
            USA]; Kline, J. [Los Alamos National Laboratory, Los Alamos, New
          Mexico 87545, USA]; Knauer, J. [Laboratory for Laser Energetics, University of
            Rochester, Rochester, New York 14623, USA]; Kritcher, A. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Kyrala, G. [Los Alamos National Laboratory, Los Alamos, New
          Mexico 87545, USA]; Landen, O. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; LePape, S. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Li, C. K. [Plasma Science and Fusion Center, Massachusetts Institute of
            Technology, Cambridge, Massachusetts 02139, USA]; Lindl, J. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Ma, T. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Mackinnon, A. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Macphee, A. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA] (ORCID:0000000341604479); Manuel, M. J.-E. [Plasma Science and Fusion Center, Massachusetts Institute of
            Technology, Cambridge, Massachusetts 02139, USA]; Meyerhofer, D. [Laboratory for Laser Energetics, University of
            Rochester, Rochester, New York 14623, USA]; Moody, J. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Moses, E. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Nagel, S. R. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Nikroo, A. [General Atomics, San Diego, California 92186,
            USA] (ORCID:0000000288550378); Pak, A. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Parham, T. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Petrasso, R. D. [Plasma Science and Fusion Center, Massachusetts Institute of
            Technology, Cambridge, Massachusetts 02139, USA] (ORCID:0000000258834054); Prasad, R. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Ralph, J. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Rosen, M. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Ross, J. S. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Sangster, T. C. [Laboratory for Laser Energetics, University of
            Rochester, Rochester, New York 14623, USA]; Sepke, S. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Sinenian, N. [Plasma Science and Fusion Center, Massachusetts Institute of
            Technology, Cambridge, Massachusetts 02139, USA]; Sio, H. W. [Plasma Science and Fusion Center, Massachusetts Institute of
            Technology, Cambridge, Massachusetts 02139, USA] (ORCID:000000017274236X); Spears, B. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Springer, P. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Tommasini, R. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Town, R. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Weber, S. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]; Wilson, D. [Los Alamos National Laboratory, Los Alamos, New
          Mexico 87545, USA]; Zacharias, R. [Lawrence Livermore National Laboratory,
          Livermore, California 94550, USA]

doi:10.1063/1.4900621

Nanosecond Pulsed High Frequency Discharges (NPHFD) are gaining popularity over conventional spark and arc discharges as they have been shown to increase energy efficiency, enhance ignition probability and sustained kernel growth, and offer more flexibility and control for ignition applications under various conditions. Hence, it is important to determine the impact of different factors such as the optimal pulse energy, background flow conditions, inter-pulse time, mixture equivalence ratio, etc. on the success of ignition of premixed mixtures with NPHFD. This work presents a numerical investigation of the morphology of ignition kernel development with both single-pulse and multiple-pulse discharges. Nanosecond non-equilibrium plasma discharges are modeled between pin-pin electrodes in a subsonic ignition tunnel with quiescent and flowing premixed mixtures of methane and air. Large eddy simulations (LES) are conducted to investigate the reasons for successful and failed ignition in different scenarios. A single pulse discharge in the presence of electrodes, in a quiescent medium, elucidates the gas recirculation pattern caused by the plasma pulse which results in a separated toroidal kernel from the primary ignition kernel between the electrodes. Convection heat loss to the mean flow results in quenching of the high temperature, radical-rich hot-spots creeping on the electrode walls, and leaving only the semi-toroidal kernel to propagate downstream. Finally, simulations with multiple pulses with different inter-pulse times have been conducted to analyze the synergistic effect of overlapping kernels with high temperature and OH concentration, which has been attributed as the primary reason for higher ignition probabilities in the “fully coupled” regime reported in the experiments. Successful ignition kernel formation is reported with 3 pulses at a pulse repetition frequency of 300 kHz in the fully coupled regime. This kernel volume was almost 4 times, and develops in two-thirds the time, compared to the ignition kernel volume formed by the single pulse discharge with the same total energy. Ten pulses with twice as much total energy were deposited at a much lower frequency of 2 kHz, which resulted in disjoint hot-spots that fail to form an ignition kernel in the decoupled regime.

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