Investigation of Metallic and Metallic Glass Hollow Spheres for Fusion Target Application
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INVESTIGATION OF METALLIC AND METALLIC GLASS HOLLOW SPHERES FOR FUSION TARGET APPLICATION*
MARK C. LEE, JAMES M. KENDALL, TAYLOR G. WANG, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA
91109, and WILLIAM L. JOHNSON, W. M. Keck Laboratory of Engineering Materials, Institute of Technology, Pasadena, CA 91125
California
ABSTRACT High quality metallic and metallic-glass microballoons (MMB and MGMB) are of considerable interest for fusion target applications on account of the intrinsic properties of these materials such as high density, high strength and high atomic number. We report the first successfully formed submillimeter and millimeter spherical shells of tin and of a gold-lead-antimony alloy by means of the hollow-jet instability technique developed by one of us (JMK). Examination of tin specimens by means of SEM has revealed that surface quality varied from poor to excellent. Whereas this metal has been employed only as a convenient and inexpensive material, the gold alloy is important because it is hard, has high atomic number, and may be solidified into the amorphous state through the provision of a modest cooling rate. We have produced AuPbSb spherules up to 1.5 mm in diameter using LN2 or chilled methanol as a coolant, and have found that these amorphous samples possess a superb surface smoothness compatible with fusion target requirements. Hollow spheres currently made of this alloy have an average O.D. of 2000 /m.
INTRODUCTION Nuclear-fusion technology holds the potential to supply a practically unlimited amount of energy to meet our nation's needs beyond the year 2000. The technology is being developed at a very rapid pace, especially that of the inertial confinement fusion. High-gain fusion targets currently in use are of ablative types, consisting of hollow glass spheres with layers of heavy metal polymer and light metal coatings. The processes used to fabricate those targets are understandably extremely complex1 . It is obvious that tremendous advantages are to be gained by substituting the innermost two concentric spheres of glass and high-Z metal by a microballoon of heavy and high atomic number metallic/metallic glass. First, by choosing cleverly a metallic/metallic glass tamper system, the optimal ablative condition can be achieved between different drivers and targets. Second, the target fabrication process can be greatly simplified. Such spherical shells must be dimensionally precise, smooth, of high strength and composed of high-atomic-number materials. Tin has been used * Research supported by NASA and DOE through Contract NAS7-100.
106 as a model material in one study of metallic shells. Other metals such as lead and gold are considered. For model metallic-glass systems, four criteria must be met in this feasibility-study phase. 1. High-Z and high density. 2. Modest requirements for cooling rate . 3. Low viscosity at Tm. 4. Low Tm (
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