In DT fusion 80% of the energy released goes into 14MeV neutrons, and only the remaining 20% into charged particles. Unlike the charged particles, the uncharged neutrons cannot be confined by a magnetic field, and for this reason cannot be used for a direct conversion into electric energy. Instead, the neutrons have to be slowed down in some medium, heating this medium to a temperature of less than 10^3K, with the heat removed fom this medium to drive a turbo-generator. This conversion of nuclear into electric energy has a Carnot efficiency of about 30%. For the 80% of the energy released into neutrons, the efficiency is therefore no more than 24%. While this low conversion efficiency cannot be overcome in magnetic confinement concepts, it can be overcome in inertial confinement concepts, by surrounding the inertial confinement fusion target with a sufficiently thick layer of liquid hydrogen and a thin outer layer of boron, to create a hot plasma fire ball. The hydrogen layer must be chosen just thick and dense enough to be heated by the neutrons to 100,000K. The thusly generated, fully ionized, and rapidly expanding fire ball can drive a pulsed magnetohydrodynamic generator at an almost 100% Carnot efficiency, or possibly be used to generate hydrocarbons.
In DT fusion 80% of the energy is released in 14 MeV neutrons. To utilize this energy the neutrons must in all proposed DT fusion concepts (including the ITER) be slowed down in a medium, heating the medium up to a temperature not exceeding a few thousand degrees, from which this energy is converted into mechanical energy, and ultimately into electric energy. While the conversion from mechanical into electric energy goes at a high efficiency (90%), the conversion of the thermal energy into mechanical energy is limited by the Carnot process to about 30%. To overcome this limitation, I propose to slow down the neutrons in the combustion products of a convergent spherical detonation wave in HMX, for example, which ignites a magnetized DT target which is placed in the center of convergence, prior to the ignition of the high explosive from its surface. The thermonuclear ignition is achieved by the high implosion velocity of 50km/sec reached in the center, compressing and igniting the preheated magnetized target. Even though the thermonuclear gain of a magnetized target is modest, it can become large if it is used to ignite unburnt DT by propagating burn. There the gain can conceivably be made 1000 times larger, substantially exceeding the yield of the high explosive. And if the spherical high explosive has a radius of about 30cm, the 14 MeV DT fusion reaction neutrons are slowed down in its dense combustion products, raising the temperature in it to 100000 K. At this temperature the kinetic energy of the expanding fire ball can be converted at a high (almost 100%) efficiency directly into electric energy by an MHD Faraday generator. In this way most of the 80% neutron energy can be converted into electric energy, about three times more than in magnetic (ITER) or inertial (ICF) DT fusion concepts.
The proposed hybrid chemical-nuclear pulse fusion concept has the potential of a high nuclear into electrical energy conversion, not possible if most of the energy released in neutrons is not used to heat a plasma to high temperatures. The only drawback this concept might have is the high yield, requiring a Faraday generator of large dimensions. The expansion velocity of the fireball, of the order 100km/sec, if compared with the expansion velocity of a few km/sec for a chemical explosion, demonstrates that the micro-fusion reaction results in a thousandfold amplification of the energy in the high explosive.
Apart from its usefulness to convert DT and possibly D fusion energy into electric energy, it also has for likewise reasons a most interesting application for nuclear rocket propulsion where it eliminates the necessity of a large radiator.
Brian Wang is a Futurist Thought Leader and a popular Science blogger with 1 million readers per month. His blog Nextbigfuture.com is ranked #1 Science News Blog. It covers many disruptive technology and trends including Space, Robotics, Artificial Intelligence, Medicine, Anti-aging Biotechnology, and Nanotechnology.
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