Browsing by Author "Wilks, S.C."

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Conservation laws and conversion efficiency in ultraintense laser-overdense plasma interactions
    (AIP Publishing LLC, 2013) Levy, M.C.; Wilks, S.C.; Tabak, M.; Baring, M.G.
    Particle coupling to the oscillatory and steady-state nonlinear force of an ultraintense laser is studied through analytic modeling and particle-in-cell simulations. The complex interplay between these absorption mechanisms—corresponding, respectively, to “hot” electrons and “hole punching” ions—is central to the viability of many ultraintense laser applications. Yet, analytic work to date has focused only on limiting cases of this key problem. In this paper, we develop a fully relativistic model in 1-D treating both modes of ponderomotive light absorption on equitable theoretical footing for the first time. Using this framework, analytic expressions for the conversion efficiencies into hole punching ions and into hot electrons are derived. Solutions for the relativistically correct hole punching velocity and the hot electron Lorentz factor are also calculated. Excellent agreement between analytic predictions and particle-in-cell simulations is demonstrated, and astrophysical analogies are highlighted.
  • Thumbnail Image
    Item
    Development of an interpretive simulation tool for the proton radiography technique
    (AIP Publishing LLC., 2015) Levy, M.C.; Ryutov, D.D.; Wilks, S.C.; Ross, J.S.; Huntington, C.M.; Fiuza, F.; Martinez, D.A.; Kugland, N.L.; Baring, M.G.; Park, H.-S.
    Proton radiography is a useful diagnostic of high energy density (HED) plasmas under active theoretical and experimental development. In this paper, we describe a new simulation tool that interacts realistic laser-driven point-like proton sources with three dimensional electromagnetic fields of arbitrary strength and structure and synthesizes the associated high resolution protonradiograph. The present tool’s numerical approach captures all relevant physics effects, including effects related to the formation of caustics. Electromagnetic fields can be imported from particle-in-cell or hydrodynamic codes in a streamlined fashion, and a library of electromagnetic field “primitives” is also provided. This latter capability allows users to add a primitive, modify the field strength, rotate a primitive, and so on, while quickly generating a high resolution radiograph at each step. In this way, our tool enables the user to deconstruct features in a radiograph and interpret them in connection to specific underlying electromagnetic field elements. We show an example application of the tool in connection to experimental observations of the Weibel instability in counterstreaming plasmas, using ∼108 particles generated from a realistic laser-driven point-like proton source, imaging fields which cover volumes of ∼10 mm3. Insights derived from this application show that the tool can support understanding of HED plasmas.
  • Thumbnail Image
    Item
    Scaled laboratory experiments explain the kink behaviour of the Crab Nebula jet
    (Springer Nature, 2016) Li, C.K.; Tzeferacos, P.; Lamb, D.; Gregori, G.; Norreys, P.A.; Rosenberg, M.J.; Follett, R.K.; Froula, D.H.; Koenig, M.; Seguin, F.H.; Frenje, J.A.; Rinderknecht, H.G.; Sio, H.; Zylstra, A.B.; Petrasso, R.D.; Amendt, P.A.; Park, H.S.; Remington, B.A.; Ryutov, D.D.; Wilks, S.C.; Betti, R.; Frank, A.; Hu, S.X.; Sangster, T.C.; Hartigan, P.; Drake, R.P.; Kuranz, C.C.; Lebedev, S.V.; Woolsey, N.C.
    The remarkable discovery by the Chandra X-ray observatory that the Crab nebulaﾒs jet periodically changes direction provides a challenge to our understanding of astrophysical jet dynamics. It has been suggested that this phenomenon may be the consequence of magnetic fields and magnetohydrodynamic instabilities, but experimental demonstration in a controlled laboratory environment has remained elusive. Here we report experiments that use high-power lasers to create a plasma jet that can be directly compared with the Crab jet through well-defined physical scaling laws. The jet generates its own embedded toroidal magnetic fields; as it moves, plasma instabilities result in multiple deflections of the propagation direction, mimicking the kink behaviour of the Crab jet. The experiment is modelled with three-dimensional numerical simulations that show exactly how the instability develops and results in changes of direction of the jet.