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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
AuthorJohns, Heather M.
Mancini, Roberto C.
Mayes, Daniel C.
Smalyuk, V. A.
Regan, S. P.
Delettrez, J. A.
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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.
|Journal Title||Physics of Plasmas|
|Rights||In Copyright (All Rights Reserved)|
|Rights Holder||AIP Publishing LLC. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in 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 and may be found at https://doi.org/10.1063/1.4940672.|