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Title: Early Stage of Implosion in Inertial Confinement Fusion: Shock Timing and Perturbation Evolution

Abstract

In this paper we model the shock timing and early perturbation growth of directly driven targets measured on the OMEGA laser system.

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Laboratory for Laser Energetics, University of Rochester, Rochester, NY
Sponsoring Org.:
USDOE
OSTI Identifier:
875442
Report Number(s):
DOE/SF/19460-648
1607; 2005-150
DOE Contract Number:
FC52-92SF19460
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 13
Country of Publication:
United States
Language:
English

Citation Formats

Goncharov, V.N., Gotchev, O.V., Vianello, E., Boehly, T.R., Knauer, J.P., McKenty, P.W., Radha, P.B., Regan, S.P., Sangster, T.C., Skupsky, S., Smalyuk, V.A., Betti, R., McCrory, R.L., Meyerhofer, D.D., and Cherfils-Clerouin, C. Early Stage of Implosion in Inertial Confinement Fusion: Shock Timing and Perturbation Evolution. United States: N. p., 2006. Web. doi:10.1063/1.2162803.
Goncharov, V.N., Gotchev, O.V., Vianello, E., Boehly, T.R., Knauer, J.P., McKenty, P.W., Radha, P.B., Regan, S.P., Sangster, T.C., Skupsky, S., Smalyuk, V.A., Betti, R., McCrory, R.L., Meyerhofer, D.D., & Cherfils-Clerouin, C. Early Stage of Implosion in Inertial Confinement Fusion: Shock Timing and Perturbation Evolution. United States. doi:10.1063/1.2162803.
Goncharov, V.N., Gotchev, O.V., Vianello, E., Boehly, T.R., Knauer, J.P., McKenty, P.W., Radha, P.B., Regan, S.P., Sangster, T.C., Skupsky, S., Smalyuk, V.A., Betti, R., McCrory, R.L., Meyerhofer, D.D., and Cherfils-Clerouin, C. Tue . "Early Stage of Implosion in Inertial Confinement Fusion: Shock Timing and Perturbation Evolution". United States. doi:10.1063/1.2162803.
@article{osti_875442,
title = {Early Stage of Implosion in Inertial Confinement Fusion: Shock Timing and Perturbation Evolution},
author = {Goncharov, V.N. and Gotchev, O.V. and Vianello, E. and Boehly, T.R. and Knauer, J.P. and McKenty, P.W. and Radha, P.B. and Regan, S.P. and Sangster, T.C. and Skupsky, S. and Smalyuk, V.A. and Betti, R. and McCrory, R.L. and Meyerhofer, D.D. and Cherfils-Clerouin, C.},
abstractNote = {In this paper we model the shock timing and early perturbation growth of directly driven targets measured on the OMEGA laser system.},
doi = {10.1063/1.2162803},
journal = {Physics of Plasmas},
number = ,
volume = 13,
place = {United States},
year = {Tue Jan 31 00:00:00 EST 2006},
month = {Tue Jan 31 00:00:00 EST 2006}
}
  • Excessive increase in the shell entropy and degradation from spherical symmetry in inertial confinement fusion implosions limit shell compression and could impede ignition. The entropy is controlled by accurately timing shock waves launched into the shell at an early stage of an implosion. The seeding of the Rayleigh-Taylor instability, the main source of the asymmetry growth, is also set at early times during the shock transit across the shell. In this paper we model the shock timing and early perturbation growth of directly driven targets measured on the OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495more » (1997)]. By analyzing the distortion evolution, it is shown that one of the main parameters characterizing the growth is the size of the conduction zone D{sub c}, defined as a distance between the ablation front and the laser deposition region. Modes with kD{sub c}>1 are stable and experience oscillatory behavior [V. N. Goncharov, Phys. Rev. Lett. 82, 2091 (1999)]. The model shows that the main stabilizing mechanism is the dynamic overpressure due to modulations in the blow-off velocity inside the conduction zone. The long wavelengths with kD{sub c}<1 experience growth because of coupled Richtmyer-Meshkov-like and Landau-Darrieus instabilities [L. D. Landau and E. M. Lifshitz, Fluid Mechanics (Pergamon, New York, 1982)]. To match the simulation results with both the shock timing and perturbation growth measurements a new nonlocal thermal transport model is developed and used in hydrocodes.« less
  • ''Measuring Implosion Dynamics through rhoR Evolution in Inertial-Confinement Experiments'' .....(OAK/B202) The areal density (rhoR) of D3He filled plastic capsules imploded at OMEGA has been measured at shock coalescence (1.7 ns) and, 400 ps later, during compressive burn, through the energy downshift of 14.7-MeV D3He protons. In this time interval, the azimuthally averaged rhoR changes from 13{+-}2.5 to 70{+-}8 mg/cm2. The experiments demonstrate that fuel-shell mix is absent in the central regions at shock coalescence, and that the shell has no holes during compressive burn. We conjecture that rhoR asymmetries measured during compressive burn may be seeded by the time ofmore » shock coalescence.« less
  • An innovative technique has been developed and used to measure the shock propagation speed along two orthogonal axes in an inertial confinement fusion indirect drive implosion target. This development builds on an existing target and diagnostic platform for measuring the shock propagation along a single axis. A 0.4 mm square aluminum mirror is installed in the ablator capsule which adds a second orthogonal view of the x-ray-driven shock speeds. The new technique adds capability for symmetry control along two directions of the shocks launched in the ablator by the laser-generated hohlraum x-ray flux. Laser power adjustments in four different azimuthal conesmore » based on the results of this measurement can reduce time-dependent symmetry swings during the implosion. Analysis of a large data set provides experimental sensitivities of the shock parameters to the overall laser delivery and in some cases shows the effects of laser asymmetries on the pole and equator shock measurements.« less
  • The viability of inertial confinement fusion depends crucially on implosion symmetry. A spherical three-dimensional hydrocode called PLATO has been developed to model the growth in asymmetries during an implosion. Results are presented in the deceleration phase which show indistinguishable linear growth rates, but greater nonlinear growth of the Rayleigh-Taylor instability than is found in two-dimensional cylindrical simulations. The three-dimensional enhancement of the nonlinear growth is much smaller than that found by Sakagami and Nishihara.
  • Mechanisms that induce implosion asymmetries in ion-driven inertial confinement fusion (ICF) targets are identified and investigated by studying the two-dimensional hydrodynamic response of the heavy-ion-driven HIBALL target (Boch, in {ital Heavy} {ital Ion} {ital Inertial} {ital Fusion}, AIP Conf. Proc. No. 152, Washington, DC (American Institute of Physics, New York, 1986), p. 23) in planar geometry. The implosion of the multilayered, single-shell target is subjected to two symmetry-reducing mechanisms: (1) spatial beam intensity nonuniformities and (2) target material interface perturbations. In self-consistent numerical calculations, the target implosion symmetry is found to be sensitive to spatial variations in beam energy depositionmore » resulting from interface perturbations in the path of the beam and coherent intensity variations in the beam itself. The asymmetries in beam energy absorption perturb the flow in the target absorption layer. If the resulting fluid perturbations are seeded at the hydrodynamically unstable pusher--fuel interface, they can grow with rates comparable to the Rayleigh--Taylor instability when lateral wavelengths are comparable to the payload shell thickness. Coherent variations in beam intensity as small as 5%--10% at low intensity (1 TW/cm{sup 2}) and 1% at high intensity (1000 TW/cm{sup 2}) limit the usable target implosion energy.« less