Shell stability and conditions analyzed using a new method of extracting shell areal density maps from spectrally resolved images of direct-drive inertial confinement fusion implosions
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Authors
Johns, Heather M.
Mancini, Roberto C.
Nagayama, Taisuke
Mayes, Daniel C.
Tommasini, R.
Smalyuk, V. A.
Regan, S. P.
Delettrez, J. A.
Issue Date
2016
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Article
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Abstract
In warm target direct-drive inertial confinement fusion implosion experiments performed at the OMEGA laser facility, plastic micro-balloons doped with a titanium tracer layer in the shell and filled with deuterium gas were imploded using a low-adiabat shaped laser pulse. Continuum radiation emitted in the core is transmitted through the tracer layer and the resulting spectrum recorded with a gated multi-monochromatic x-ray imager (MMI). Titanium K-shell line absorption spectra observed in the data are due to transitions in L-shell titanium ions driven by the backlighting continuum. The MMI data consist of an array of spectrally resolved images of the implosion. These 2-D space-resolved titanium spectral features constrain the plasma conditions and areal density of the titanium doped region of the shell. The MMI data were processed to obtain narrow-band images and space resolved spectra of titanium spectral features. Shell areal density maps, rho L(x,y), extracted using a new method using both narrow-band images and space resolved spectra are confirmed to be consistent within uncertainties. We report plasma conditions in the titanium-doped region of electron temperature (T-e) = 400 +/- 28 eV, electron number density (N-e) = 8.5 x 10(24) +/- 2.5 x 10(24) cm(-3), and average areal density <rho R > = 86 +/- 7 mg/cm(2). Fourier analysis of areal density maps reveals shell modulations caused by hydrodynamic instability growth near the fuel-shell interface in the deceleration phase. We observe significant structure in modes l = 2-9, dominated by l = 2. We extract a target breakup fraction of 7.1 +/- 1.5% from our Fourier analysis. A new method for estimating mix width is evaluated against existing literature and our target breakup fraction. We estimate a mix width of 10.5 +/- 1 mu m. (C) 2016 AIP Publishing LLC.
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Johns, H. M., Mancini, R. C., Nagayama, T., Mayes, D. C., Tommasini, R., Smalyuk, V. A., … Delettrez, J. A. (2016). Shell stability and conditions analyzed using a new method of extracting shell areal density maps from spectrally resolved images of direct-drive inertial confinement fusion implosions. Physics of Plasmas, 23(1), 012709. doi:10.1063/1.4940672
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1070-664X