Laser absorption, mass ablation rate, and shock heating in direct-drive inertial confinement fusion

Journal Article · Tue May 15 00:00:00 EDT 2007 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.2671690· OSTI ID:20975063

Regan, S P; Epstein, R; Goncharov, V N; Igumenshchev, I V; Li, D; Radha, P B; Sawada, H; Seka, W; Boehly, T R; Delettrez, J A; Gotchev, O V; Knauer, J P; Marozas, J A; Marshall, F J; McCrory, R L; McKenty, P W; Meyerhofer, D D; Sangster, T C; Shvarts, D; Skupsky, S ^[1]

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1. Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623-1299 (United States)

Direct-drive laser absorption, mass ablation rate, and shock heating are experimentally studied on the OMEGA Laser System [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] to validate hydrodynamics simulations. High-gain, direct-drive inertial confinement fusion target implosions require accurate predictions of the shell adiabat {alpha} (entropy), defined as the pressure in the main fuel layer to the Fermi-degenerate pressure, and the implosion velocity of the shell. The laser pulse shape determines the shell adiabat and the hydrodynamic efficiency determines the implosion velocity. A comprehensive set of measurements tracking the flow of energy from the laser to the target was conducted. Time-resolved measurements of laser absorption in the corona are performed on spherical implosion experiments. The mass ablation rate is inferred from time-resolved Ti K-shell spectroscopic measurements of nonaccelerating, solid CH spherical targets with a buried tracer layer of Ti. Shock heating is diagnosed in planar-CH-foil targets using time-resolved x-ray absorption spectroscopy and noncollective spectrally resolved x-ray scattering. The highly reproducible experimental results achieved with a high level of laser drive uniformity [S. P. Regan et al., J. Opt. Soc. Am. B 22, 998 (2005)] constrain the modeling of direct-drive energy coupling. A detailed comparison of the experimental results and the simulations reveals that a single-value flux limiter in the thermal transport model cannot explain all of the experimental observables. Simulations of laser absorption measurements need a time-dependent flux limiter to match the data. Modeling of both resonance absorption and nonlocal effects in the electron thermal conduction from the critical density to the ablation front are underway to resolve the observed discrepancies.

• OSTI ID: 20975063
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 5 Vol. 14; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ABLATION
ABSORPTION SPECTROSCOPY
HYDRODYNAMICS
IMPLOSIONS
INERTIAL CONFINEMENT
LASERS
LIMITERS
PLASMA
PLASMA DENSITY
PLASMA DIAGNOSTICS
PLASMA PRESSURE
PLASMA SIMULATION
PULSE SHAPERS
RESONANCE ABSORPTION
SHOCK HEATING
TIME DEPENDENCE
TIME RESOLUTION
X-RAY DIFFRACTION
X-RAY SPECTROSCOPY