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Author Schneider, M. B. ♦ MacLaren, S. A. ♦ Widmann, K. ♦ Meezan, N. B. ♦ Hammer, J. H. ♦ Yoxall, B. E. ♦ Bell, P. M. ♦ Benedetti, L. R. ♦ Bradley, D. K. ♦ Callahan, D. A. ♦ Dewald, E. L. ♦ Döppner, T. ♦ Eder, D. C. ♦ Edwards, M. J. ♦ Hinkel, D. E. ♦ Hsing, W. W. ♦ Kervin, M. L. ♦ Landen, O. L. ♦ Lindl, J. D. ♦ May, M. J.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY ♦ PLASMA PHYSICS AND FUSION TECHNOLOGY ♦ CAPSULES ♦ CYLINDERS ♦ ENERGY TRANSFER ♦ GOLD ♦ HEATING ♦ HOT PLASMA ♦ HYDRODYNAMIC MODEL ♦ IMAGES ♦ KEV RANGE ♦ LASER CAVITIES ♦ LASER RADIATION ♦ PEAK LOAD ♦ PHOTON BEAMS ♦ RADIATION FLUX ♦ THERMONUCLEAR FUELS ♦ TIME RESOLUTION ♦ US NATIONAL IGNITION FACILITY ♦ WALLS ♦ X RADIATION ♦ X-RAY SPECTRA
Abstract At the National Ignition Facility, a thermal X-ray drive is created by laser energy from 192 beams heating the inside walls of a gold cylinder called a “hohlraum.” The x-ray drive heats and implodes a fuel capsule. The laser beams enter the hohlraum via laser entrance holes (LEHs) at each end. The LEH radius decreases as heated plasma from the LEH material blows radially inward but this is largely balanced by hot plasma from the high-intensity region in the center of the LEH pushing radially outward. The x-ray drive on the capsule is deduced by measuring the time evolution and spectra of the x-radiation coming out of the LEH and correcting for geometry and for the radius of the LEH. Previously, the LEH radius was measured using time-integrated images in an x-ray band of 3–5 keV (outside the thermal x-ray region). For gas-filled hohlraums, the measurements showed that the LEH radius is larger than that predicted by the standard High Flux radiation-hydrodynamic model by about 10%. A new platform using a truncated hohlraum (“ViewFactor hohlraum”) is described, which allows time-resolved measurements of the LEH radius at thermal x-ray energies from two views, from outside the hohlraum and from inside the hohlraum. These measurements show that the LEH radius closes during the low power part of the pulse but opens up again at peak power. The LEH radius at peak power is larger than that predicted by the models by about 15%–20% and does not change very much with time. In addition, time-resolved images in a >4 keV (non-thermal) x-ray band show a ring of hot, optically thin gold plasma just inside the optically thick LEH plasma. The structure of this plasma varies with time and with Cross Beam Energy Transfer.
ISSN 1070664X
Educational Use Research
Learning Resource Type Article
Publisher Date 2015-12-15
Publisher Place United States
Journal Physics of Plasmas
Volume Number 22
Issue Number 12


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