Absorption, reflection, and symmetry measurements have been made on spherical laser fusion targets for both single beam (highly non-symmetric), and four beam (more symmetric) irradiation, at incident laser energies of up to 250 joules. Optical, charged particle and x-ray measurement techniques are used to show the essentially symmetric behavior of the multi-beam irradiation. A measure of the effectiveness of lateral heat conductivity is obtained from a comparison of symmetric and non-symmetric irradiation results. Greatpr thp 30% of the incident laser energy at an intensity of 1015-1010W/cm4 results in elevated plasma temper4tures. The energy deposited in high energy photons is less than 10-3 of the absorbed energy. No distinct high energy Ion component is observed and, in any case, less than a few percent of the absorbed energy resides in ions of energies >10keV/nucleon. Time resolved optical diagnostics have uncovered the presence of an "after pulse" emitted from the plasma at the laser frequency but following the trailing edge of the heating pulse.
Structural information provided by computed tomography (CT) can be used for quality control and optimization of processes for manufacturing better materials. The squeeze casting method for producing metal matrix composites involves infiltrating a preform of ceramic fibers with molten metal under high pressure. Part quality can be improved if CT is used before infiltration to determine if the preforms have the desired distribution of fibers and are free of defects. Measurements do not require uniform shapes, and CT systems can even be used to obtain accurate densities on complicated part shapes that are not amenable to bulk density measurements based on weight and size. With this quantitative distribution information as a guide, preform production can be modified to produce either a more uniform fiber distribution or to selectively increase the fiber concentration in critical areas. Problems occurring during later stages of processing can be detected in CT images of the completed part. For example. CT can be used to detect unreinforced regions in metal matrix composites caused by cracking of the preform during the squeeze casting process. CT scans of completed parts can also detect and distinguish variations in structure such as microporosity.
Solid targets of pure deuterium or deuterium-bearing compounds are required for experiments designed to explore the feasibility of laser fusion as a source of energy. This paper deals with three aspects of the targets used in this application, namely, (i) the selection of suitable compounds which provide optimum heating by the laser radiation, (ii) the fabrication of appropriately sized and shaped targets from these compounds, and (iii) the positioning of these targets in laser-irradiation experiments. Spherical targets of lithium deuteride, deuterated polyethylene, and paraffins with diameters of 50–200 μ are considered, as well as 400 μ cylindrical extrusions of deuterium ice. Detailed descriptions are given of the apparatus and techniques used to position these targets in the focal region of the laser radiation.
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