Tomography of laser fusion plasmas Page: 2 of 21
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TOMOGRAPHY OF LASER FUSION PLASMAS*
N. M. Ceglio
Lawrence Livermore Laboratory U.4 p. *, o. W.d 5a. Dq
University of California
Livermore, California 94550
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Experimental programs exist in a number of laboratories throughout the
world to test the feasibility of using powerful laser systems to drive the
implosion of hydrogen isotope fuel to thermonuclear burn conditions. In a
typical experiment multiple laser beams are focused onto a glass microshell
(typically 50 pm - 200 um diameter) filled with an equimolar D-T gas mixture
(Fig. 1). X-ray and particle emissions from the target provide important in-
formation about the hydrodynamic implosion of the glass shell and the associ-
ated compression and heating of the D-T fuel. Standard diagnostics for imaging
such emissions are the grazing incidence reflection (GIR) x-ray microscope and
the pinhole camera. Recently, a particular coded imaging technique, Zone Plate
Coded Imaging (ZPCI), has been successfully used for x-ray and particle micros-
copy of laser fusion plasmas. ZPCI is highly attractive for investigating laser
produced plasmas because it possesses a tomographic capability not shared by
either the GIR or pinhole imaging techniques. This presentation provides a
brief discussion of the tomographic potential of ZPCI. In addition, the first
tomographic x-ray images (tomographic resolution - 74 pm) of a laser produced
plasma are presented.
ZPCI was first proposed by Mertz2 for stellar x-ray imaging. It has also
enjoyed considerable attention in the field of nuclear medicine. ZPCI is a two-
step imaging technique (Fig. 2). In the first step the radiation distribution
to be imaged casts a shadowgraph through a Fresnel zone plate (coded aperture)
onto a photographic emulsion or other detector array. The shadowgraph is a coded
image of the source emission distribution. Image reconstruction (decoding) is
achieved via procedures similar to those used in holography. The shadowgraph
transparency is illuminated with a coherent light source. The Fresnel diffraction
pattern of the transmitted light produces a three dimensional reconstruction of
the original source distribution. The image is inverted, revered front to back,
and magnified by the ratio of the (coded) image to object distances.
The tomographic capability of ZPCI may be understood very simply. Consider
a three dimensional source distribution represented by three, non-coplanar points
(Fig. 3). Each source point will cast a zone plate shadow onto the shadowgraph
plane. The size and position of each shadow in the shadowgraph uniquely charac-
terizes the position of its associated source point. Points close to the coded
aperture project large shadows, distant points project small shadows, off-axis
points project off-axis shadows, and so on. Upon reconstruction each zone plate
*idork performed under the auspices of the U.S. Energy Research and Development
Administration under contract No. W-7405-Eng-48.
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Ceglio, N.M. Tomography of laser fusion plasmas, article, August 2, 1977; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc1056429/m1/2/: accessed February 22, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.