Patent Number: 042773059
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION FIG. 1 discloses a perspective view of the device comprising the preferred embodiments of the invention. As shown, the device comprises a beam generator 10, an annular beam forming system 12, and a linear theta-pinch device 14. Beam generator 10 comprises a high power laser, ion, or electron beam generator. Annular beam forming system 12 comprises standard optical means for generating an annular beam from a solid laser beam or standard propagation devices for generating annular beams from solid ion and electron beams generated by beam generator 10. Therefore, the output beam 18 from annular beam forming means 12 constitutes either a laser, ion, or electron annular beam. The annular beam 18 is propagated into the theta-pinch device 14. The theta-pinch device 14 comprises a single turn theta-pinch coil 20 having an approximately 5 cm radius and having a length of 50-100 cm. The theta-pinch coil is attached to a fast capacitor bank 22 which is capable of generating a magnetic field of nearly 100 KGauss. The theta-pinch coil is filled with an ionized working fluid at a pressure of 1-10 mm Hg. A fuel capsule 24 is disposed along the axis of the theta-pinch coil 20 at the center of the axial length of the device as shown in the cutaway view of the theta-pinch device 14 of FIG. 1. The fuel capsule comprises a thermonuclear fuel such as DT as a solid, a hollow shell, or high pressure gas. As shown in FIG. 1, a low density or void section 26 is surrounded by high density DT 28 which is further surrounded by a tamper 30 which normally comprises a high-Z material, which is further surrounded by a pusher 32 which comprises a low-Z material. Surrounding the outside of theta-pinch coil 20 is an insulation layer 34 which is further surrounded with a liquid lithium blanket 36. In operation, the theta-pinch device 14 operates in a conventional manner. Discharge of the fast discharge capacitor bank 22 generates a converging theta-pinch shock which establishes an imploding dense hot plasma sheath 38 from the ionized working fluid. The dense hot plasma sheath 38 causes pusher 32 of fuel capsule 24 to evaporate amd generate a fuel element plasma layer. Subsequently, according to one embodiment of the invention, annular beam 18 is directed at the fuel element plasma layer and adds sufficient energy to this plasma layer to cause the tamper 30 and high density fuel 28 to accelerate toward the center of the fuel capsule 24 to implode and generate a hot thermonuclear plasma. Simultaneously, the cylindrical plasma sheath 38 is driven towards the axis of the theta-pinch coil 20 to increase compression of the thermonuclear fuel at the center of the fuel capsule 24. The timing of the beam energy deposition is such that the theta-pinch and beam generated compression waves arrive at the center of the fuel capsule 24 nearly simultaneously. According to another embodiment of the present invention, annular beam 18 is aligned with cylindrical plasma sheath 38 to dispose energy in the cylindrical plasma sheath. The addition of beam energy to the cylindrical plasma sheath 38 causes the innerpart of the sheath 38 to implode rapidly on fuel capsule 24 with the combined energy of the annular beam 18 and the theta-pinch coil 20. FIG. 2 is a schematic diagram of an end view of the theta-pinch device 14 of FIG. 1. Capacitor bank 22 discharges energy into cylindrical theta-pinch coil 20 which generates an advancing magnetic field 40. The advancing magnetic field in turn generates a cylindrical plasma sheath 38 having an advancing density front 42 which converges on fuel capsule 24. The relative densities are more clearly shown in the graph of FIG. 3 which is a plot of density within the theta-pinch coil 20 versus radial distance from the center of the theta-pinch coil 20. As shown, the advancing magnetic field 40 generates a high density plasma sheath 38 which travels toward the axis of the theta-pinch coil. As a result, the density outside the advancing magnetic field is somewhat lower than the background fill density 44. The graph of FIG. 3 additionally shows the shell density 46 and density of the thermonuclear DT fuel 48. According to the operational sequence described above, the major contribution to the implosion energy of the fuel capsule 24 is provided by the laser, electron, or ion beam. The advancing magnetic field 40 generated by capacitor bank 22 and theta-pinch coil 20, however, helps to precompress and accelerate the thermonuclear fuel by evaporation of the pusher 32 in one embodiment, and provides a high density cylindrical plasma sheath 38 which is capable of absorbing beam energy in another embodiment of the invention. In both embodiments, the magnetic field 40 inhibits radial heat conduction to the wall and protects the theta pinch coil 20 from charged ions during fuel burn and improves stability of fuel implosion with an addeded bias field 40. The working fluid from which the plasma sheath 38 is generated is selected according to the particular embodiment utilized. Use of DT gas to generate plasma sheath 38 has the advantage of providing a non-contaminating material which is capable of thermonuclear burn during the implosion process. However, the absorption characteristics of the DT plasma are less desirable than higher atomic weight gases such as Argon or similar gases. Yet, as disclosed in co-pending application Ser. No. 882,024, entitled "E-Beam Driven Linear Intense Neutron Source", filed Feb. 28, 1978 by Lester E. Thode now abandoned in favor of a continuation-in-part application, Ser. No. 071.603 filed Aug. 31, 1979, deposition of electron beam energy in plasmas having 10.sup.17 particles/cm.sup.3 and greater can be accomplished by providing a high voltage, i.e. 10 MeV to 30 MeV, low .mu./.gamma. electron beam. The present invention therefore provides a means for generating hot plasmas in the kilovolt range by utilizing two sources of energy, i.e. magnetic and beam energy, which supplement each other to implode a thermonuclear fuel capsule. This overcomes many of the problems associated with prior art systems. The implosive nature of the present system eliminates end loss problems typically encountered in theta-pinch devices and laser heated solenoids. The possibility of fuel target damage encountered typically in laser fusion targets is eliminated by deposition of beam energy in the cylindrical plasma sheath 38 or fuel element plasma layer. This also aleviates problems associated with beam focusing, pulse shape and duration, and energy absorption properties of the fuel capsule. The magnetic field of the theta-pinch device 14 functions to protect the cylindrical wall from fusion reaction products and allows recovery of magnetic energy during fuel expansion to increase overall efficiency of the device. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described, and that subject matter disclosed herein shall not be precluded from being later claimed in the present application or a continuation, continuation-in-part, or reissue application.