Patent Number: 043449115
Section: summary

This invention relates to inertial fusion systems and particularly to means for protecting inner structural components of such inertial fusion systems from the x-rays, neutrons, plasma, shock effects, etc. produced by implosion of fusion targets therein. For decades, efforts have been carried out to utilize fusion energy as a source of useful power. Fusion energy should: (1) be an abundant source, (2) be safe, (3) be compatible with the environment, and (4) be technically and economically feasible. Inasmuch as estimated reserves of fusion fuel sources appear to provide the capability of supplying projected electrical energy needs for several hundred years, thus satisfying item 1, efforts have been directed to satisfying items 2-4. Early and currently ongoing efforts are directed to the production of fusion power by the magnetic confinement approach, with more recent efforts also being directed to the inertial confinement approach. With the advent of lasers, early inertial confinement efforts have been directed to the development of laser initiated fusion power plants, as exemplified by U.S. Pat. Nos. 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, wherein a fuel containing target is injected into an implosion or combustion chamber and imploded by one or more laser beams directed into the chamber. More recently, development efforts have also been directed to utilizing ion and electron beams for imploding fusion targets within a chamber, as exemplified by U.S. Pat. Nos. 3,892,950 issued July 1, 1975 to J. R. Freeman et al; and 3,899,681 issued Aug. 12, 1975 to E. H. Beckner et al. With the experimental verification in 1974 and 1975 of the production of neutrons, x-rays, etc. by the implosion of tiny fusion fuel targets via inertial confinement, and with the verification in 1976 that the neutrons thus produced were indeed thermonuclear, efforts have been substantially increased in the field of inertial fusion reactor development. As the result of the experimental efforts in producing fusion neutrons from the tiny targets, it was found that implosion of such resulted in very little damage to the wall surfaces, etc. of the implosion or combustion chamber. However, it is recognized that implosion of larger targets at a selected repetition rate will be necessary to produce useful power by inertial confinement systems, and thus means must be developed to protect the implosion chamber from the x-rays, high-energy neutrons, etc., produced by the implosion of these larger or higher yield targets. At the presently contemplated values of .rho.R (=product of final density and final radius of the imploded fusion target) of 1-2 for laser fusion experiments, approximately 75% of the fusion energy thus produced is in the form of high energy neutrons, with the remainder being primarily x-rays and target debris. A neutron moderating material is thus required to convert neutron kinetic energy to thermal energy. Lithium has been considered as such a moderating material, as exemplified by above-referenced U.S. Pat. No. 3,624,239. A DT fusion reactor must also breed its own tritium, and the only tritium-producing reactions with sufficiently high cross sections to be useful are those involving lithium: EQU .sup.6 Li+n.fwdarw..sup.4 He+T EQU .sup.7 Li+n.fwdarw..sup.4 He+T+n To obtain a T breeding ratio &gt;1.0, the .sup.7 Li reaction is required to offset unavoidable neutron losses; this reaction produces a tritium atom without depleting the neutron population, although said reaction has an energy threshold of 4 MeV and a much lower reaction cross section than the .sup.6 Li reaction. At the same time, it is also necessary to protect the first exposed wall in the interior of the fusion chamber from the debris, x-rays, and high energy neutrons (approximately 25% of the total energy) produced by each microexplosion. To accomplish the protection of the chamber, the breeding of its own tritium, and the dissipation of the heat produced by the conversion of neutron kinetic energy, the so-called "wetted wall" approach has been proposed, as exemplified by above-referenced U.S. Pat. No. 3,762,992, utilizing liquid lithium. The so-called "dry wall" approach has been proposed wherein a sacrificial metal or ceramic liner is placed between the fusion chamber and the blanket which interacts with the x-rays and debris. In addition, the so-called magnetically protected wall uses a solenoid to divert the pellet debris away from the wall into collectors. While these prior approaches have been calculated to provide adequate protection from x-rays and debris, the structures are still subject to damage from high energy neutrons, and only for a period of time, possibly as long as 1-3 years. A need exists by which structural wall protection can be accomplished more effectively and more economically. SUMMARY OF THE INVENTION The invention is directed to means for protecting the first or inner wall of an inertial fusion implosion chamber from high energy neutrons, x-rays, charged particles, and debris produced by the implosion of fusion fuel targets in the chamber, as well as providing a neutron moderating material to convert neutron kinetic energy to thermal energy, and for breeding tritium. This is accomplished in accordance with the invention by providing a blanket within the chamber which utilizes a fluidized wall similar to a waterfall composed of liquid or lithium or of solid pellets of lithium-ceramic. Calculations indicate that the lithium waterfall approach will provide adequate protection of the chamber for about 30 years. Therefore, it is an object of this invention to provide means for protecting the first wall of a fusion chamber from x-rays, neutrons, etc. created by implosion of a fusion fuel target therein. A further object of the invention is to provide in a fusion reaction chamber a blanket which utilizes a fluidized wall for protecting the inner surface of the chamber. Another object of the invention is to provide means for the protection of the inner components of a fusion reaction chamber from x-rays, neutrons, etc. while providing for tritium breeding and for conversion of neutron kinetic energy to thermal energy. Another object of the invention is to provide a lithium waterfall blanket for use in laser fusion implosion chambers. Other objects of the invention will become readily apparent from the following description and accompanying drawings.