Abstract:
An apparatus and method for positron fueled ramjet operation is provided including a convection chamber for a ramjet comprising a rate of absorption of gamma rays that yields a uniform heating of the convection chamber to a temperature sufficient to sustain ramjet operation. The convection chamber may comprise at least one open ended cylinder, a plurality of concentrically arranged cylinders, a plurality of rods, a honeycomb structure or other structures for absorbing gamma rays. A ramjet powered by gamma rays is also provided that includes a housing forming a fluid passageway. A reaction vessel is positioned within the housing, and arranged in flow communication with a source of positrons. A gamma ray absorption assembly is positioned within the fluid passageway so that as positrons interact with electrons and annihilate, gamma rays impinge upon the gamma ray absorption assembly. A method of heating a convection chamber of a ramjet engine is also provided in which a plurality of positrons are annihilated by interaction with an equal plurality of electrons at a controlled rate of annihilation so as to produce a steady emission of gamma rays. The gamma rays are absorbed by a convection chamber of the ramjet engine wherein the convection chamber comprises a rate of absorption of gamma rays that yields a uniform heating of the convection chamber to a temperature sufficient to sustain ramjet operation.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to propulsion systems and, more particularly, to a ramjet propulsion system that utilizes positron annihilation as a fuel source.  
         BACKGROUND OF THE INVENTION  
         [0002]    Ramjet engines and their operation are well known in the art as a propulsion system for high speed flying vehicles, e.g., jet aircraft, missiles, rockets, etc. A ramjet engine generally operates by capturing and compressing an air stream impinging upon an inlet structure in the ramjet engine. The compressed air stream provides oxygen for mixing with a fuel, such as a suitable hydrocarbon, which is supplied to a combustion chamber located adjacent to the inlet structure in the interior of the ramjet engine. The fuel is oxidized in the combustion chamber so as to produce expanding combustion gases. The expanding combustion gases escape through a nozzle structure at supersonic velocities, and produce a forward thrust to the ramjet and the attached vehicle.  
           [0003]    A unique aspect of ramjet engines is the fact that the rate of air compression depends upon the speed of flight of the vehicle, rather than on a mechanical compressor. The high-pressure air streaming into the combustion chamber acts to prevent the air fuel mixture from effectively reacting toward the air intake end of the engine. Ramjet engines will not function until a sufficient air stream is flowing through the intake to create a high-pressure flow. Without this high-pressure stream of air, the expanding gases of the oxidizing fuel-air mixture within the combustion chamber would be expelled from both ends of the engine. Thus there is a need with all ramjet propelled systems to accelerate the vehicle from 0 or low velocity to a velocity where the ramjet will begin to operate on its own (Mach number of about 0.5-1). Typically, a ramjet propelled vehicle must be boosted to a predetermined speed by some other type of engine or vehicle.  
           [0004]    Conventional ramjets powered by the oxidation of chemical fuels have a limited utility. For example, a ramjet weighing about forty kilograms, and combusting about four to five kilograms of chemical fuel, may stay aloft at about a one thousand meter altitude for approximately one-half hour. This is sufficient time for such applications as rocket and missile boosters; however, it is far to short a time for use of such a device in unmanned surveillance and ordnance delivery systems, passenger aircraft, airborne weather data acquisition and recordation systems, and airborne telecommunications systems or sensor systems, such as, cellular telephone hubs, or environmental, agriculture, and the like monitors. Thus there is a need for a ramjet powered vehicle that is fueled in such a way that its total flight time is significantly extended, out to at least several days or weeks.  
           [0005]    Propulsion systems using matter/antimatter annihilation have been postulated in the prior art as a substitute for chemical based fuel sources. For example, antiproton annihilation fueled engines have been proposed where the matter/antimatter annihilation yields at least ten orders of magnitude greater energy per unit density than stored chemical energy. However, antiproton-proton annihilation results in the emission of pi-mesons and gamma rays in excess of nuclear reaction thresholds. Anti-electrons (“positrons”) occur naturally as a by-product of radioactive decay, e.g., radioactive sodium emits positrons. Positrons are significantly less massive than an antiproton, so that their annihilation with electrons results in gamma ray emissions that are below nuclear reaction thresholds, making such annihilation acceptable for use in close proximity to humans, and in the atmosphere. Positrons may be gathered and stored in a variety of ways. Using simple energy density scaling, a ramjet powered by as little as one milligram of positrons may stay aloft at the same altitude for multiple hours, if not days.  
           [0006]    It would be advantageous to have a ramjet engine that did not require conventional chemical fuels, but rather utilized matter/antimatter annihilation as a source of power.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention provides a structure that yields a heat transfer function that is directly analogous to a combustion chamber for a conventional ramjet, but has a structure that provides a rate of absorption of gamma rays that yields a uniform heating of that structure, defined throughout as a “convection chamber” to a temperature sufficient to sustain ramjet operation. In one embodiment, the convection chamber comprises at least one open ended cylinder or a plurality of concentrically arranged cylinders. In other embodiments, the convection chamber for a ramjet comprises a plurality of rods, a honeycomb structure or other means for absorbing gamma rays so as to yield a uniform heating of the absorbing means to a temperature sufficient to sustain ramjet operation.  
           [0008]    A ramjet powered by gamma rays resulting from positron/electron annihilations is also provided that includes a housing having a first open end, a second open end, and defining an interior chamber in fluid communication with the first open end and the second open end so as to form a fluid passageway. A reaction vessel is positioned within the interior chamber of the ramjet, and arranged in flow communication with a source of positrons so as to provide a flow of positrons into the reaction vessel. A gamma ray absorption assembly is positioned within the fluid passageway and adjacent to the reaction vessel so that as positrons interact with electrons and annihilate, gamma rays radiate from the reaction vessel and impinge upon the gamma ray absorption assembly. The gamma ray absorption assembly provides a function within the ramjet of the present invention that is directly analogous to a combustion chamber. In particular, gamma ray absorption assembly is uniformly heated by the absorption of a plurality of gamma rays resulting from the continuous annihilation of positrons and electrons within the reaction vessel thereby heating it to a temperature sufficient to sustain ramjet operation.  
           [0009]    A method of heating a convection chamber of a ramjet engine is also provided in which a plurality of positrons are urged into interaction with an equal plurality of electrons so as to annihilate one another at a controlled rate of annihilation thereby producing a steady emission of gamma rays. The gamma rays are absorbed by a convection chamber of the ramjet engine wherein the convection chamber comprises a rate of absorption of gamma rays that yields a uniform heating of the convection chamber to a temperature sufficient to sustain ramjet operation. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    These and other features and advantages of the present invention will be more fully disclosed in, or rendered obvious by, the following detailed description of the preferred embodiments of the invention, which are to be considered together with the accompanying drawings wherein like numbers refer to like parts and further wherein:  
         [0011]    [0011]FIG. 1 is a perspective view of an aircraft having a ramjet engine formed in accordance with the present invention;  
         [0012]    [0012]FIG. 2 is a longitudinal cross-sectional view of a ramjet engine formed in accordance with the present invention;  
         [0013]    [0013]FIG. 3 is a broken-away, cross-sectional view of a leading portion of the ramjet shown in FIG. 2;  
         [0014]    [0014]FIG. 4 is a broken-away, cross-sectional view of a trailing portion of the ramjet shown in FIG. 2;  
         [0015]    [0015]FIG. 5 is a cross-sectional view of the trailing end of the ramjet shown in FIG. 2, showing a concentric shell embodiment of a gamma ray absorption assembly formed in accordance with the present invention;  
         [0016]    [0016]FIG. 6 is a cross-sectional view of the trailing end of the ramjet shown in FIG. 2, showing a plurality of rods arranged as a gamma ray absorption assembly formed in accordance with an alternative embodiment of the present invention;  
         [0017]    [0017]FIG. 7 is a cross-sectional view of the trailing end of the ramjet shown in FIG. 2, showing a honeycomb construction arranged as a gamma ray absorption assembly formed in accordance with an alternative embodiment of the present invention; and  
         [0018]    [0018]FIG. 8 is a cross-sectional view of the trailing end of the ramjet shown in FIG. 2, showing a mesh construction arranged as a gamma ray absorption assembly formed in accordance with an alternative embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    This description of preferred embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description of this invention. The drawing figures are not necessarily to scale and certain features of the invention may be shown exaggerated in scale or in somewhat schematic form in the interest of clarity and conciseness. In the description, relative terms such as “horizontal,” “vertical,” “up,” “down,” “top” and “bottom,” “leading” and “trailing,” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing figure under discussion. These relative terms are for convenience of description and normally are not intended to require a particular orientation. Terms including “inwardly” versus “outwardly,” “longitudinal” versus “lateral” and the like are to be interpreted relative to one another or relative to an axis of elongation, or an axis or center of rotation, as appropriate. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. The term “operatively connected” is such an attachment, coupling or connection that allows the pertinent structures to operate as intended by virtue of that relationship. In the claims, means-plus-function clauses are intended to cover the structures described, suggested, or rendered obvious by the written description or drawings for performing the recited function, including not only structural equivalents but also equivalent structures.  
         [0020]    Referring to FIGS. 1 and 2, a ramjet  1  formed in accordance with one embodiment of the present invention comprises a housing  5 , a positron source  7 , a transfer conduit  8 , a reaction vessel  9 , and a gamma ray absorption assembly  11 . Housing  5  is often formed as an open ended tube (typically a prolate spheroid) that defines an interior chamber  14  having a first open end  17  and a second open end  19 . Other tubular shapes and profiles are also possible. It will be understood that conventional structural features may be fitted to the exterior and interior of housing  5  so as to allow for the mounting of ramjet  1  on or within a vehicle  20 , e.g., an aircraft, a missile, a rocket, torpedo, or the like vehicle. The various known metals that are normally used in aircraft construction may be used to fabricate housing  5 , e.g., aluminum, titanium, tungsten, and their alloys, as well as, carbon fiber composite materials.  
         [0021]    Positron source  7 , transfer conduit  8 , and reaction vessel  9  are housed within a diffuser housing  18  of the type normally employed in conventional ramjets. The leading portion  15  of diffuser housing  18  (positioned within first open end  17  of housing  5 ) is sized so as to fully enclose and support positron source  7 , and the trailing portion  16  of diffuser housing  18  is substantially cylindrical so as to enclose and support transfer conduit  8  and reaction vessel  9 . Leading portion  15  of diffuser housing  18  is conventionally shaped so as to reduce the airspeed, and hence the kinetic energy, of air streaming through first open end  17 . Such a leading portion of diffuser housing  18  will effect the transfer of air stream kinetic energy into a nearly equal increase in potential energy in the form of increased air pressure within interior chamber  14 . Diffuser housing  18  is formed from the group of metals and composite materials known to those skilled in the art for their structural integrity and durability when subjected to ultra-high velocity fluids (greater than 700 miles per hour) and ultra-high temperatures (greater than 1,000° K), e.g., tungsten, titanium, molybdenum, and their well known alloys.  
         [0022]    First open end  17  and second open end  19  are in fluid communication, via interior chamber  14 , such that a fluid passageway is defined through housing  5 . First open end  17  serves as an inlet port for fluids, such as air, to enter ramjet  1  and second open end  19  serves as an exhaust port. Second open end  19  may be configured as a thrust direction and orifice adjustable nozzle of the type that is familiar to those of ordinary skill in the art.  
         [0023]    Referring to FIGS. 3 and 4, positron source  7  is positioned within leading portion  15  of diffuser housing  18 , and may comprise an antimatter penning trap  21  that is suitable for storing a plurality of positrons, e.g., several hundred micrograms of positrons. Positrons may exist for a time in the form of a positronium atom which is the bound state of an positron and its antiparticle the electron. Positronium atoms may also be stored in positron source  7 , and utilized in connection with the present invention. Antimatter penning traps often comprise a highly evacuated, cryostatic magnetic “bottle” of the type well known in the art. For example, U.S. Pat. Nos.: 4,867,939; 4,982,088; 4,990,856; 5,248,883; 5,977,554; and 6,160,263, teach such penning traps and their operation, and are hereby incorporated herein by reference.  
         [0024]    For example, penning traps are well known to include a series of coaxially arranged and spaced-apart electrically conductive rings  22  (FIG. 3) that are cooled to about four degrees above absolute zero (minus two hundred and sixty-nine degrees Celsius) during operation. Such temperatures are often achieved through the immersion of the device in liquid helium. Rings  22  are located within a very strong (six Tesla) magnetic field that is directed along the direction of the central axis of the rings, with each ring  22  being interconnected with a source of varying electric potential, via cables or the like  24 . Such magnetic fields may be supplied, for example, by the inclusion of magnets  23  formed from super-conducting materials, and cooled with a portion of the liquid helium in which positron source  7  is immersed. Conductive rings  22  are positioned within an enclosure  25  which is evacuated to about 10 −13  torr, and cooled to about four degrees above absolute zero. Appropriate insulation materials (not shown) may be packed around positron source  7  within leading portion  15  of diffuser  18  to aid in the maintenance of the interior of enclosure  25  at cryogenic temperatures. Vacuum and/or cryogenic conduits  29  may also be interconnected to enclosure  25  so as to help regulate the vacuum and temperature levels of penning trap  21 .  
         [0025]    A static potential is often applied between rings  22  which generates a static potential well along a vertical axis. At the same time, a repulsive potential along a horizontal plane is generated which is overcome by superimposing a static, a very strong (six Tesla) magnetic field along a vertical axis. The horizontal motion of the trapped positrons (or positronium atoms) is a composite of circular cyclotron orbits primarily due to the magnetic field and a circular drift magnetron motion in response to the cross product of the electric field and the magnetic field vectors, i.e., E×B about the vertical axis. The positrons are thus confined in the space defined by the ring electrodes. Penning traps can provide long term confinement of a plurality of positrons or positronium atoms for several days or even weeks.  
         [0026]    The positron mass required to be stored in positron source  7  (for a 250 kW power input to ramjet  1 , and 10 4  second, 2.8 hr flight) is determined by the following relationship: N=(2.5×10 5 ×10 4 ×1)J×1 microgram/180×10 6  J, or about 13.9 micrograms of positrons supplied from positron source  7 .  
         [0027]    Alternatively, a specialized “atom-chip” container that utilizes quantum wire and quantum dot technology to store hundreds of micrograms of positronium atoms, may be employed as positron source  7 , substantially indefinitely.  
         [0028]    Positron source  7  is positioned within leading portion  15  of diffuser  18  so as to be adjacent to first open end  17 . A cylindrical container that is about 13 cm in diameter and 100 cm long would provide adequate space for a penning trap  21  or other suitable receptacle of positrons or source of positronium atoms. An exit port  26  is formed on a trailing end of positron source  7  that opens into transfer conduit  8 . Suitable structures, e.g., struts, beams, brackets  28 , electrical cables  24 , and vacuum and cyrogenic conduits  29  are provided for supporting and servicing positron source  7  and the entire structure of diffuser  18 . These struts, beams, and brackets  28 , electrical cables  24 , and vacuum and cryogenic conduits  29  are of the type that are regularly used for supporting, positioning and servicing precision electronic components and cooled systems in aircraft and aircraft engine environments.  
         [0029]    Transfer conduit  8  preferably comprises a tube having an open proximal end  31 , a closed distal end  33 , and an internal passageway  35 . Reaction vessel  9  is typically coextensive with transfer conduit  8 , and is bounded by closed distal end  33 . Transfer conduit  8  extends from positron source  7  into interior chamber  14 , with internal passageway  35  being in fluid communication with exit port  26 . Positrons or positronium atoms (shown representationally at referenced numeral  37  in FIG. 4) that are discharged into internal passageway  35  from positron source  7  are both confined and urged through transfer conduit  8  by an electrostatic lens assembly  40  within passageway  35 .  
         [0030]    Electrostatic lens assembly  40  is adapted to be sealingly mounted to positron source  7 , via exit port  26 , and may take several forms. For example, electrostatic lens assembly  40  may comprise a plurality coaxially aligned, cylindrical tubes  43  that are formed from a highly conductive metal, e.g., copper or its alloys. Tubes  43  are individually interconnected to a source of variable high voltage electrical potential (not shown) in a manner well known to those of ordinary skill in the aircraft design arts. Tubes  43  are sized so as to fit within transfer conduit  8  with gaps  47  defined between predetermined groups of tubes  43  so as to form strong electric field gradients adjacent to the edge portions of the tubes that are positioned on either side of a gap  47 .  
         [0031]    Electrostatic lens assembly  40  normally does not extend into reaction vessel  9 , although it may do so, as needed, for a particular design purpose. Both transfer conduit  8  and reaction vessel  9  are maintained at a similar evacuated state, i.e., internal pressure, as positron source  7 . Electrons are generally available within reaction vessel  9  for interaction with, and annihilation of positrons  37  entering reaction vessel  9  from transfer conduit  8 . In the case of positronium atoms, an electron will already be paired with a positron so that once the paired structure decays an annihilation will occur. It will be understood that for each positron/electron annihilation that occurs within reaction vessel  9 , two 0.511 Mev (million electron-volt) gamma rays will be created which will move away from the locus of annihilation in opposite directions (shown schematically at reference numeral  38  in FIG. 4).  
         [0032]    Gamma ray absorption assembly  11  is positioned in substantially surrounding relation to reaction vessel  9 , i.e., substantially surrounding relation to trailing portion  16  of diffuser housing  18  which is a locus of positron-electron annihilations. Gamma ray absorption assembly  11  comprises a structure, e.g., material type and/or density (e.g., a graduated radial or longitudinal density) or physical shape, spacing or graded thickness, that provides a predetermined rate of absorption of gamma rays so as to provide for a uniform distributed absorption of the gamma rays throughout the assembly. This uniformly distributed absorption of gamma rays  38  results in a uniform heating across absorption assembly  11 . Rate of absorption of gamma rays by absorption assembly  11  means the rate at which gamma rays are captured by the atoms that constitute the structure of the device. This is an intrinsic characteristic of gamma ray absorption assembly  11 . Temperatures in the range of from about 2000° K to 3500° K, or more (i.e., temperatures sufficient to sustain ramjet operation at supersonic airspeeds) can be easily achieved, maintained, and controlled in gamma ray absorption assembly  11 . Of course, lower or higher temperatures are easily achievable, e.g., in the range from about 1,000° K to about 4500° K, as needed, to obtain efficient ramjet operation in the present invention.  
         [0033]    More particularly, a gamma ray absorption assembly  11  formed in accordance with the present invention will exhibit a rate of absorption of 0.511 Mev gamma rays  38  emanating from the positron/electron annihilations occurring in reaction vessel  9 , that yields a uniform radial heating of the structure. One example of a gamma ray absorption assembly  11  that has been identified as performing adequately is one or more substantially cylindrical shells  60  assembled so as to be in substantially concentric coaxial relation with one another, with reaction vessel  9  within interior chamber  14  (FIGS.  2 - 5 ). Shells  60  may be formed from a suitable metal having a high gamma ray absorption cross-section, e.g., tungsten or its alloys, or a carbon material, such as silicon carbide or its equivalents.  
         [0034]    Although a single shell comprising a radially graded density, i.e. a density that increases with radial distance from a source of gamma rays  38  will function according to the invention, a plurality of concentric shells  60  of varying thickness and radial distance from reaction vessel  9  are often employed since this arrangement improves the fluid flow characteristics within ramjet  1 . Additionally, plurality of concentric shells  60  may be coated with an appropriate material, e.g., boron nitride, to help ameliorate tungsten oxidation and burning at low temperatures. Each of concentric shells  60  may be constructed and arranged so as to be at differing radial offsets from reaction vessel  9 , and are supported by struts, beams, brackets  28 , as needed for structural integrity. Also, each individual shell  60  may have one or more different structural or material characteristics as compared to other ones of shells  60 , e.g., thinner or thicker, round leading or trailing edges, more or less dense, coated or uncoated, etc.  
         [0035]    Many other structures may also be used in connection with gamma ray absorption assembly  11  (FIGS.  6 - 8 ). By way of example only, and not limitation, an assembly of one or more rods  62 , honeycomb  64 , mesh  66 , tubes (hollow rods) as well as other fluid flow compatible, aerodynamically shaped solid or porous bodies, or combinations thereof will work adequately with ramjet  1 , as long as each of these alternatives are arranged and selected so that the resulting “convection chamber” structure provides a maximized gamma ray absorption gradient yielding a uniform heating of the structure.  
         [0036]    Ramjet  1  operates by first causing a high velocity (normally supersonic) air stream to enter first open end  17  of housing  5  where leading portion  15  of diffuser housing  18  acts to reduce the air speed and hence kinetic energy of the air as it passes through open end  17 . The acceleration to supersonic airspeeds is normally accomplished by conventional, chemically fueled engines that are attached to vehicle  20 . At supersonic speeds, a shock compression of the air flow will occur depending upon the free stream Mach number. The location of this shock will vary. To avoid the shock from entering convection chamber  11 , leading end  15  of diffuser  18  may be movable, forwardly or rearwardly relative to housing  5 , by the inclusion of electromechanical drive means of the type known in the art. The reduction in kinetic energy of the air stream entering first open end  17 , via diffuser  18 , results in a nearly equal increase in potential energy of the air stream in the form of an increased air pressure within interior chamber  14 .  
         [0037]    This higher-pressure air enters gamma ray absorption assembly  11  where it is superheated through conductive heat transfer from, e.g., shells  60 , rods  62 , honeycomb  64 , or mesh  66 , thereby significantly increasing the gas pressure within housing  5 , i.e., significantly adding to the potential energy stored in the air stream passing through ramjet  1 . It will be understood that gamma ray absorption assembly  11  provides a convective heat transfer function within ramjet  1  that is directly analogous to the function of a conventional combustion chamber positioned within a prior art ramjet, and adapted for the burning of chemical fuels. In particular, gamma ray absorption assembly  11 , e.g., shells  60 , rods  62 , honeycomb  64 , or mesh  66 , will be uniformly heated to approximately 3,000° K by the absorption of 0.511 Mev gamma rays resulting from the continuous annihilation of positrons and electrons within reaction vessel  9 . Thus gamma ray absorption assembly  11  is generally referred to as a “convection chamber”, whether or not it takes a structural form that includes a compartment or void space defined within interior chamber  14 .  
         [0038]    As the compressed stream of gas passes over the gamma ray absorption assembly, it will be superheated through conductive contact with the surfaces of the heated material. The superheated gas is ejected rearwardly, from second open end  19  of housing  5 , thereby converting the potential energy stored in the air stream to kinetic energy in the form of an exhaust of gas traveling at a velocity that is significantly greater than the flight speed of vehicle  20  to which ramjet  1  is assembled. The efficiency of ramjet  1  in converting the energy stored within gamma ray absorption assembly  11  into kinetic energy of the air stream leaving second open end  19  depends upon the ratio of the pressure in interior chamber  14  to the ambient air pressure surrounding ramjet  1 . This pressure ratio, in turn, depends upon the flight speed of vehicle  20 , or, more exactly, upon the flight Mach number.  
         [0039]    It is to be understood that the present invention is by no means limited only to the particular constructions herein disclosed and shown in the drawings, but also comprises any modifications or equivalents within the scope of the claims.