Patent Number: 042696593
Section: summary

BACKGROUND OF THE INVENTION This invention relates to the generation of energy, and more particularly, this invention relates to a device for generating neutrons by a fusion plasma. Nuclear fusion is one of the primary nuclear reactions. The name indicates an energy-releasing rearrangement collision which can occur between various isotopes of low atomic number. There is a great deal of interest in fusion plasmas in the hope that they may be used to produce useful power. There are several advantages to a fusion reaction which make it so appealing. Since a primary fusion fuel, deuterium, occurs naturally and is obtainable in virtually inexhaustible supply (by separation of heavy hydrogen from water, one atom of deuterium occurring per 6500 atoms of hydrogen), solution of the fusion power problem can permanently solve the problem of energy production for mankind with far less pollution of his environment. As a power source, the small amount of radioactive waste products from the fusion reaction is another argument in its favor as opposed to fusion of uranium. Also, a fusion reactor, by virtue of the small amount of fusionable material in the reactor at any time, would not explode. In a nuclear fusion reaction the close encounter of two energy rich nuclei results in a mutual rearrangement of their nucleons (protons and neutrons) to produce two or more reaction products, together with a release of energy. The energy usually appears in the form of kinetic energy of the reaction products, although when energetically allowed, part may be taken up as energy of an excited state of the product nucleus. In contrast to neutron-produced nuclear fission reactions, colliding nuclei, because they are positively charged, require a substantial initial relative kinetic energy to overcome their mutual electrostatic repulsion so that reaction can occur. The largest reaction cross-section for fusion is between a mixture of the heavy isotopes of hydrogen, deuterium and tritium, which is a hundred times larger than the next most probably fuel mixture, that of deuterium itself. Thus, the mixture of deuterium and tritium and deuterium alone are the primary fuels being considered initially. Nuclear fusion reactions can be self sustaining if they are carried out at a very high temperature. That is to say, if the fusion fuel exists in the form of a very hot ionized gas of stripped nuclei and free electrons, called a "plasma", the agitation energy of the nuclei can overcome their mutual repulsion, causing reactions to occur. This is the mechanism of energy generation in the stars and in the fusion bomb. It is also the method attempted for the controlled generation of fusion energy. In this latter instance, the plasma is generated and confined by either electromagnetic fields or inertially. However, all experiments have failed to produce a self-sustaining reaction primarily because of the inability to confine the fusion reaction for a sufficient amount of time. Previous nuclear fusion reactors for controlled, self sustaining nuclear fusion reaction have been built in order to establish the feasibility of generating useful power. These reactors, however, have not met with success, primarily because the amount of energy used to maintain the plasma has been greater than the energy generated. The reaction in such reactors has ordinarily been carried out in a very hot but tenuous fuel gas mixture of hydrogen isotopes. To avoid immediate quenching of the reaction, it has been carried out in an evacuated chamber, with means provided to prevent the reacting fuel from coming in contact with the chamber walls. The use of magnetic fields has been the method for achieving this. All of these reactors have failed, primarily because of the breakup of the plasma. There are, however, nuclear fusion research reactors which produce energy in short bursts and emit fast neutrons. Two types of confinement are presently being used; the first and older approach is generally referred to as magnetic confinement, while the second and newer approach is called dynamic confinement. Magnetic confinement takes advantage of the fact that at the elevated temperatures required for fusion to occur (order of 10.sup.8 degrees) the atoms are stripped of their electrons (i.e., they are ionized) and are strongly affected and can be controlled by magnetic fields. Dynamic confinement relies upon the short times required (order of 10.sup.-9 seconds) for a high density solid (10.sup.23 atoms/cc) to meet the Lawson criteria of n.tau..apprxeq.10.sup.14 sec/cc for net energy production. Briefly, in one method, a short burst of a very high energy density flux is focused upon, and completely around, a small solid pellet of fusion fuel with the aid of split beams from an appropriate laser. The outer surface of the pellet is very quickly vaporized and almost explosively pushes itself away from the pellet. The pressure on the remaining solid increases sufficiently to increase its density to perhaps 10.sup.3 -10.sup.5 g/cm.sup.3. The resulting implosion is sufficient to initiate and sustain the fusion reaction and produce energetic neutrons. SUMMARY OF THE INVENTION The present invention overcomes the previously accepted notion that a magnetically confined fusion plasma device must be self sustaining and eliminates the necessity for continuously maintaining the plasma. Rather, the present invention utilizing either magnetic confinement or inertial confinement contemplates constantly generating new plasmas in "pulses" so that the net effect is an approximation of a self sustaining reaction with the consequent emission of neutrons. The present invention contemplates a plenum, or reaction, chamber wherein a fusion reaction is conducted in the same manner as in the prior art, that is, using a fuel such as deuterium, deuterium-tritium, lithium, mixtures thereof, or a mixture of protons and boron and confining the resulting plasma by an electromagnetic field or using inertial confinement with its laser apparatus. In addition, a so-called "working gas" is injected which surrounds the plasma and moves from the inlet end of the reaction chamber to the outlet end carrying the plasma with it. Neutrons are emitted by the fusion reaction as in the prior art and are utilized in the same manner as in the prior art. But, an added advantage of the present invention is that when the plasma is carried beyond the confining magnetic field, it releases its remaining energy to the working gas and this remaining energy can be recovered as electrical power, for instance, using magnetohydrodynamic techniques. It is, therefore, a primary object of the present invention to provide a method and means for generating neutrons using a plasma which is free of the aforementioned and other such disadvantages. It is another object of the present invention to provide a method and means for generating neutrons in a pulsed manner thereby eliminating the necessity for continuously maintaining the plasma. It is a further object of the present invention to provide a method and means for generating neutrons using a plasma wherein at least a portion of otherwise lost energy may be recovered. In addition to the advantages described above, the present invention offers the important advantage of direct energy conversion. An important use for the device is the extraction of energy as electricity. The working fluid, moving through the plenum chamber, will be absorbing energy from some of the unavoidable losses from the reacting pulses and the walls. Thus, even before the reactions in the pulses have been completed and their energy released, the average energy of the working fluid has already increased to probably some significant fraction of an ev. In this case, the working fluid is in a state of partial ionization. The high speed passage of the charged-particle products through a channel or tube and a suitable magnetic field would then produce electrical energy, at the expense of energy in the flowing plasma. As energy is extracted from the working fluid as electricity, it would be constantly replaced from the energy released from the plasma pulses until they are used up. The rates at which the energy is released and extracted should be tailored so that the temperature of the working gas remains below a level at which it would overcome the thermal properties of wall materials. It is here recognized that the concept of extracting electric power directly from a flowing plasma in the presence of an appropriate magnetic field (instead of going through the conventional thermal cycle) is not new. A large amount of theoretical and experimental investigations have been conducted for about two decades in order to exploit the magnetohydrodynamic (MHD) generation of electricity. The problem with previous systems is that, like conventional rocket engines, thermal energy is introduced in a concentrated form in one location, i.e., in a combustion or plenum chamber. Even when the working fluid is doped with materials with low ionization potentials, such as cesium, the percentage of energy invested in ionization, which can be extracted as electricity, is small, again due to wall material limitations. The difference in the present approach is substantial. First, the energy available from thermonuclear reactions is enormous. Second, only a small part of the available energy is initially invested in ionization. As this energy is extracted as electricity, it is immediately and continuously replaced in the flow from the remaining energy in the plasma pulses, almost as though the electrical energy were directly extracted from the pulses, and some very likely will be. Thus, the idea is to take full advantage of the properties of the wall materials over a major portion of the chamber and nozzle (or tube) so that the maximum amount of total energy involved is increased by at least one to two orders of magnitude. In general, there are two types of energetic particles created in thermonuclear reactions, charged particles and fast neutrons. There is an important aspect of the distribution of energy between the charged and uncharged particles. It is clear that the neutrons will escape from the reacting system and deposit their energy elsewhere. Only the energy of the charged particles will be retained within the reaction region, constrained by the electromagnetic fields. Hence, only this energy, at most, will be available internally to compensate for energy losses and to sustain the thermonuclear reactions. A significant portion of the energy would be deposited in the walls and structure by fast neutron moderation. In a suitable lithium blanket, some of the neutrons could breed the tritium required in the fusion reaction. Some, or possibly most, of the thermal content of the walls can be reintroduced into the cycle by regenerative cooling. Thus, the entering working gas, while still relatively cool compared with the reacting region, would contain a significant amount of thermal energy at the beginning of the cycle. While, as presently envisioned, a major portion of the energy will be directly converted to electricity, the remaining thermal energy could economically be converted in a conventional thermal cycle. The latter facilities would be much smaller than if they had to convert all of the energy. If the thermal cycle is not used, thermal pollution will be significantly increased. It is, therefore, another object of the present invention, consistent with the foregoing objects, to provide a method and means to extract energy, other than from neutrons, from a pulsed plasma source.