Patent CA-2923259-A1 (CA)
Title: Method and system for inertial confinement fusion reactions
Inventor: BIRNBACH CURTIS A
IPC: H01J35/22
Filed: 2007-05-30
Abstract: METHOD AND SYSTEM FOR INERTIAL CONFINEMENT FUSION REACTIONS FIELD OF THE INVENTION [0001]    The present invention relates to methods and systems for extracting energy from fusion reactions. BACKGROUND OF THE INVENTION [0002]    It is widely recognized that controlled fusion offers a clean and plentiful energy source. However, despite billions of dollars invested, only limited success has been achieved in creating an efficient, self-sustaining fusion reaction. All prior approaches have been limited by three major factors: (a) Only a single means of energy extraction is used. (b) Instead of focusing on Direct Drive X-ray driven reactions, the bulk of the work has been focused on indirect drive reactions, particularly using large lasers as drivers. (c) Hydrodynamic Instability is a serious problem. This occurs when the compression of the target pellet is not sufficiently uniform. It gives rise to local thermal non-uniformity which, in turn, causes local cooling. This results in an unsymmetrical burn of the fuel. [0003]    Energy can be extracted from a fusion reaction by two primary means:  Thermal and Electrical. Thermal extraction is a straightforward application of the Rankine Thermal Cycle, which is used in almost every electrical power plant. In this process, a coolant is heated, the heated coolant used to turn a turbine, and the turbine used to turn a generator. This process has a nominal 55% efficiency. [0004]    It is both possible and practical to extract electricity directly from fusion plasma. This has been demonstrated many times, and is a process with an efficiency of about 85%. The disadvantage of this technique to prior art fusion power systems is that it produces high voltage DC. High voltage DC is difficult to work with and, more importantly, not suitable for long distance power transmission and distribution. It cannot be readily or efficiently shifted in voltage as AC power can.     [0005]      Hydrodynamic Instability is a major problem that the designer of every fusion power system faces. Formally known as Rayleigh-Taylor Instability, it is a problem that arises from non-uniform compression of the fuel pellet. Non-uniformities in excess of 1% in compression result in the formation of "jets" of energy that surge outward and locally cool the target pellet. The current generation of laser driven fusion systems use multiple beams (as many as 192 in one system) to attempt to provide a sufficiently uniform compression of the fuel pellet. [0006]      It would be desirable to provide a system for extracting energy from controlled fusion reactions in which both thermal energy and high voltage DC energy are extracted. [0007]      It would be desirable if extracted high voltage DC energy can be used as an energy source to sustain controlled fusion reactions. [0008]      It would be further desirable to design a system from extracting energy form controlled fusion reactions, with a high hydrodynamic stability for achieving highly uniform compression of fuel pellets. SUMMARY OF THE INVENTION [0009]    One embodiment of the invention provides a system for extracting energy from controlled fusion reactions. The system includes a central target chamber for receiving fusion target material. A plurality of energy drivers are arranged around the target chamber so as to supply energy to fusion target material in the chamber to initiate a controlled fusion reaction of the material, releasing energy in the forms of fusion plasma and heat. A  plurality of means for extracting energy from the fusion reaction are provided, and comprise means to extract high voltage DC power from the fusion plasma; and means to extract thermal energy from the central target chamber. [00010]     The foregoing embodiment increases efficiency of a fusion power system by extracting both high voltage DC energy and thermal energy. [00011] Another embodiment of the invention provides a system for extracting energy from controlled fusion reactions wherein the plurality of energy drivers are powered by an energy storage means. The energy storage means receives power from a first power supply and provides start-up and make-up power, and a second power supply derives energy from high voltage DC power extracted from the fusion plasma. The "start-up power" is the total energy required for initiate the fusion reaction and the "make-up power" is the energy that is added to the energy from the second power supply to maintain operation of the fusion reaction. [00012] The foregoing embodiment achieves high efficiency by using the high voltage DC  power extracted from the fusion reaction as a source of power for the energy drivers that drive the fusion reactions. This means that most of the energy required to drive the fusion reaction is derived from the (previous) fusion reaction itself. [00013] A further embodiment of the invention provides a system for extracting energy from controlled fusion reactions in which each of the plurality of energy drivers comprises a unitary apparatus. The unitary apparatus produces both (a) an x-ray pulse for causing the fusion target material to undergo a controlled fusion reaction so as to cause energy release in the forms of fusion plasma and heat, and (b) RF energy to simultaneously heat the fusion target material. [00014]     The foregoing embodiment of the invention has the ability to produce an RF heating pulse simultaneously with the x-ray drive pulse without reducing efficiency.  This allows the use of RF heating to increase the efficiency of the fusion power system at little additional cost and with no energy penalty. [00015]     A still further embodiment of the invention provides a fusion power system in which an apodizing structure is associated with each energy driver for reshaping the wavefront of the x-ray pulse to be concave from the perspective of the fusion target material. [00016]     The foregoing embodiment of the invention corrects the wavefront errors that give rise to Rayleigh-Taylor Hydrodynamic Instability by means of the mentioned Apodizing Filter. As the target pellet is a sphere, the Apodizing filter is used to change the shape of the compression wavefront to a highly concave surface whose radius matches the radius of the target. By this means, the wavefront "wraps around" one face of the target and provides totally uniform compression of the target. [00017]    A direct benefit of the use of Apodizing Filters to correct the compression wavefront is that the number of beams used to illuminate the target is reduced. Instead of the 192 beams that the National Ignition Facility Fusion Reactor at Lawrence Livermore lab in California uses, the current embodiment of the invention may allow the use of as far fewer beams, such as 6.  This directly reduces the cost and size of the reactor, while increasing its reliability.