Patent Number: 042723205
Section: summary

This invention relates to targets for implosion by an energy source, such as one or more laser beams, and more particularly to a high density laser-driven target. In recent years much effort has been directed to inertial confinement fusion systems wherein a target is imploded by an energy source such as a laser or electron beam machine. U.S. Pat. No. 3,378,446 issued Apr. 16, 1968 to J. R. B. Whittlesey; 3,489,645 issued Jan. 13, 1970 to J. W. Daiber et al; 3,624,239 issued Nov. 30, 1971 to A. P. Fraas; 3,723,246 issued Mar. 27, 1973 to M. J. Lubin; and 3,762,992 issued Oct. 2, 1973 to J. C. Hedstrom are exemplary of these inertial confinement systems. As set forth in U.S. Pat. No. 3,723,246 to M. J. Lubin inertial confinement fusion has various utilities recognized by the scientific community as excellent sources of neutrons, x-rays, alpha particles, for example, for applications in radiography, synthetic fuel production, fissile fuel production, as well as for physics studies. The advent of inertial confinement fusion wherein a tiny fusion fuel target can be imploded in an evacuated chamber without damage to the chamber or the optics involved has provided an excellent source of neutrons, etc., at a magnitude not previously available under controlled conditions. Thus, as widely recognized by the scientific community, while fusion power for electrical production has not yet been accomplished, the inertial confinement fusion techniques thus far developed have greatly advanced the state of the art. In addition to the systems of the above-referenced U.S. Patents, various inertial confinement fusion mechanisms for imploding the targets have been developed as exemplified by U.S. Pat. No. 4,017,163 issued Apr. 12, 1977, to A. J. Glass, and articles "Laser Fusion Target Illumination System" by C. E. Thomas, Applied Optics, Vol. 14, No. 6, June 1975; and "Thermonuclear Fusion Research With High-Power Lasers", Vacuum Technology, May 1975, pp 50-60 and 64, by R. R. Johnson et al. Various target designs have been proposed in the open literature for laser, electron beam, and ion beam implosion techniques as exemplified by Report UCID-17297 "A 1964 Computer Run On A Laser-Imploded Capsule", by R. E. Kidder, Mar. 28, 1973; "Implosion, Stability, And Burn Of Multishell Fusion Targets" By G. S. Fraley et al, The Fifth I.A.E.A Conference on Plasma Physics and Controlled Nuclear Fusion Research, Tokyo, Japan, Nov. 11-15, 1974 as Paper IAEA-CN-33/F55 (LA-UR-5783-MS); "Laser Driven Implosion of Hollow Pellets" by J. Nuckolls et al, presented at the above-referenced Fifth I.A.E.A. Conference (UCRL-75538); "Structured Fusion Target Designs" by R. C. Kirkpatrick et al, Nuclear Fusion 15, April 1975, pp. 333-335; "Target Compression With One Beam" by G. H. McCall et al, Laser Focus, Dec. 1974, pp. 40-43; "Electrically Imploded Cylindrical Fusion Targets" by W. S. Varnum, Nuclear Fusion 15, Dec. 1975, pp. 1183-1184; "The Calculated Performance Of Structured Laser Fusion Pellets" by R. J. Mason, Nuclear Fusion 15, Dec. 1975, pp. 1031-1043; "Low Power Multiple Shell Fusion Targets For Use With Electron And Ion Beams" by J. D. Lindl et al and "Stability and Symmetry Requirements of Electron and Ion Beam Fusion Targets" by R. O. Bangerter et al, both published in the Proceedings of the International Topical Conference on Electron Beam Research and Technology held Nov. 3-6, 1975, Albuquerque, N. M. (Printed Feb. 1976), SAND76-57122; and "Problems With Fuel Pellets For Laser-Induced Fusion", Physics Today, March 1975, pp. 17 and 20. The production of fusion neutrons by inertial confinement (laser implosion) techniques was first demonstrated in May 1974, see above-referenced Vacuum Technology article by R. R. Johnson, and "Measurement of the Ion Temperature in Laser-Driven Fusion" by V. W. Slivinsky et al, Physical Review Letters, Vol. 35, No. 16, Oct. 20, 1975, pp. 1083-1085. Since that time hundreds of targets of various configurations have been imploded by lasers and electron beam machines which have verified to the satisfaction of the scientific community that neutrons are being produced from fusion reactions. Diagnostic techniques for verifying this fact are exemplified by the above-cited Physical Review-Letters by V. W. Slivinsky et al; "Pinhole imaging of Laser-Produced Thermonuclear Alpha Particles" by V. W. Slivinsky et al, Applied Physics Letters, Vol. 30, No. 11, June. 1, 1977, pp. 555-556; "Laser-Fusion Ion Temperatures Determined by Neutron Time-Of-Flight Techniques" by R. A. Lerche et al, UCRL-79375, dated April 1977; and "Implosion Experiments With D,He.sup.3 Filled Microballons" by V. M. Slivinsky et al, UCRL-78450 Rev. II, dated Mar. 11, 1977. Such diagnostics have verified that the computer code "LASNEX", for example, accurately models current laser fusion experiments. Target fabrication techniques are at an advanced state of development with numerous mechanisms and processes having been developed, as exemplified by the above-referenced U.S. Pat. No. 3,723,246 to M. J. Lubin, and U.S. Pat. No. 3,907,477, issued Sept. 23, 1975 to T. R. Jarboe et al; No. 3,985,841 issued Oct. 12, 1976 to R. J. Turnbull et al; and No. 4,012,265 issued Mar. 15, 1977 to J. A. Rinde et al. Copending U.S. Patent Application Ser. No. 609,640 filed Sept. 2, 1975, now U.S. Pat. No. 4,035,032 issued July 5, 1977, and Ser. No. 807,108, filed June 16, 1977, now U.S. Pat. No. 4,133,854 issued Jan. 9, 1979, each in the name of C. D. Hendricks, assigned to the assignee of this application, describe and claim processes for rapidly producing fusion target. In addition numerous publications such as "Spherical Hydrogen Targets for Laser-Produced Fusion" by I. Lewkowicz, J. Phys. D: Appl. Phys., Vol. 7, 1974; "Fabrication and Characterization of Laser Fusion Targets" by C. D. Hendricks et al, American Physical Society, Division of Plasma Physics, Nov. 10-14, 1975 (UCRL-76679); and report UCRL-50021-75"Laser Program Annual Report 1975", Lawrence Livermore Laboratory, Univ. of Calif., Section 7 "Target Fabricartion", distributed Nov. 1976, pp. 343-368. Thus, while commercial fusion power reactors may be at least a decade away, the inertial confinement fusion technology has raidly advanced such that greater than 10.sup.9 fusion neutrons are being produced by existing implosion systems, which systems currently provide an excellent source of neutrons, x-rays, alpha particles, etc., which sources have not been previously available, in the magnitude now provided, to the scientific community for use in various recognized applications as exemplified above. In addition, other currently known applications for neutrons, x-rays etc., produced by the target of this invention have applications in the field of neutron crystallography, means of achieving crystal dislocation, initiation of some action such as a switch or random number generator upon receipt of a neutron pulse by a detector, calibration of diagnostics for other apparatus, fluor studies, and as a source of strong shock waves for high pressure testing. With the acceptance by the scientific community that fusion neutrons have been produced by laser imploded targets, substantial effort is now being directed toward large laser systems and a prototype inertial confinement fusion reactor. As laser capabilities increase, targets capable of producing high neutron, x-ray yield must be developed, and with, for example, the 20-beam Shiva laser system targets having high densities will be utilized to increase the yield. While laser systems prior to Shiva have been capable of attaining high fuel densities or temperatures, but not both, the higher power Shiva system will be able to increase both the fuel densities and temperatures. Thus, a need exists for a high density laser-driven target. SUMMARY OF THE INVENTION The present invention is a high density target for inertial confinement fusion applications, and is particularly applicable for implosion by high energy lasers. Basically the target is composed of a quantity of fusion fuel surrounded by a pusher shell and having an ablator-pusher shell in spaced relation with said pusher shell defining a region therebetween which is filled with low-density material. Therefore, it is an object of this invention to provide a high density target for inertial confinement fusion. A further object of the invention is to provide a high density laser-driven target. Another object of the invention is to provide a target for laser implosion utilizing a double shell geometry wherein the inner shell functions as a pusher and the spaced outer shell functions as an ablator-pusher to implode the inner shell. Other objects of the invention will become readily apparent from the following description and accopanying drawing.