Abstract:
An electromagnetic railgun ( 10 ) comprising at least two elongated high voltage rails ( 11 ), a sliding armature ( 50 ) making electrical contact with each high voltage rail ( 11 ), at least two elongated metal support beams ( 14 ) adapted to provide mechanical strength to the railgun ( 10 ), said support beams ( 14 ) being substantially parallel to the high voltage rails ( 11 ), and a plurality of metal support plates ( 30 ) aligned circumferentially around the support beams ( 14 ) and along the length of the railgun ( 10 ), said support plates ( 30 ) adapted to provide additional mechanical strength to the railgun ( 10 ); wherein the support plates ( 30 ) are electrically isolated from each other and from the support beams ( 14 ).

Description:
RELATED PATENT APPLICATIONS 
     This patent application is a continuation-in-part of commonly-owned U.S. patent application Ser. No. 12/537,482 filed Aug. 7, 2009, entitled “Railgun System”; and additionally claims the benefit of the following four commonly-owned U.S. provisional patent applications: U.S. patent application 61/283,868 filed Dec. 10, 2009, entitled “Railgun with External Rails to the Gun Bore”, U.S. patent application 61/339,328 filed Mar. 2, 2010, entitled “Railgun with Inductive and Direct Drive Options”, U.S. patent application 61/342,163, filed Apr. 8, 2010, entitled “Railgun with Rails External to the Gun Bore—Part B”, and U.S. patent application 61/404,214 filed Sep. 28, 2010, entitled “Railgun with Steel Encased Bore”, all five of which patent applications are hereby incorporated by reference in their entireties into the present patent application. 
    
    
     TECHNICAL FIELD 
     This patent application pertains generally to the field of electromagnetic launchers, and specifically to railguns. 
     BACKGROUND ART 
     The background art will be discussed in conjunction with the following numbered references:
     Reference 1. Kerrisk, J. F., “Electrical and Thermal Modeling of Railguns”,  IEEE Transactions on Magnetics , Vol. MAG-20, No. 2, March 1984, pp. 399-402.   Reference 2. Leuer, J. A., “Electromagnetic Modeling of Complex Railgun Geometries”,  IEEE Transactions on Magnetics , Vol. MAG-22, No. 6, November 1986, pp. 1584-1590.   Reference 3. Bacon, J. L., Laughlin, R. L., and Price, J. H., U.S. Pat. No. 5,454,289, Oct. 3, 1995, “Lightweight High L′ Electromagnetic Launcher”.   Reference 4. Bernardes, J. S., Stumborg, M. F., and Jean, T. E., “Analysis of a Capacitor-Based Pulsed-Power System for Driving Long-Range Electromagnetic Guns”,  IEEE Transactions on Magnetics , Vol. 39, No. 1, January 2003, pp. 486-490.   Reference 5. Ellis, R. L., Poynor, J. C., McGlasson, B. T., and Smith, A. N., “Influence of Bore and Rail Geometry on an Electromagnetic Naval Railgun System”,  IEEE Transactions on Magnetics , Vol. 41, 2004, pp. 43-48.   Reference 6. QuickField Version 5.7, Finite Analysis System, Tera Analysis, Ltd., Svendborg, Denmark, 2009, http://quickfield.com (last downloaded Nov. 1, 2010). QuickField is a finite element analysis system designed for a personal computer and is used to solve steady state and transient electromagnetic field problems defined in two dimensions.   Reference 7. Landen, D. and Satapathy, S., “Eddy Current Effects in the Laminated Containment Structure of Railguns,”  IEEE Transactions on Magnetics , Vol. 43, No. 1, January 2007.   

     Electromagnetic launchers, such as railguns, have received considerable interest due to their ability to accelerate projectiles without the use of explosives. A railgun uses the magnetic field between a pair of current-carrying high voltage rails to accelerate a current-carrying armature. Railguns are a promising non-explosive projectile launcher and have many potential applications, including weaponry and blasting holes in the earth during mining operations. For widespread use, a railgun must be economical, powerful, and durable. 
     One problem that has remained unsolved for many years has been the inability to properly confine the high voltage rails within the gun bore at power levels of interest and for useful lifetimes. During armature launch, the current in each of the rails results in a mutually repulsive force. The currents, one flowing from the gun base, or breech, and the other returning to the breech, repel each other due to standard principles of magnetism. Theoretical work published in the mid-1980s (References 1 and 2) argued that an electrically conducting containment vessel, such as a cylindrical barrel, should not be used to confine the high voltage rails. The papers showed that such a conducting cylinder could work only if the cylinder diameter was large compared to the separation distance between the rails. However, in that case, the intervening volume would need to be filled with dielectric material, and the resulting gun would be too heavy for practical use. If the conducting cylinder diameter was approximately equal to the distance between the high voltage rails, these papers indicated that the ability to convert rail current efficiently into magnetic propulsion of the armature would become vanishingly small. As a result of this, the conversion efficiency of electrical energy to kinetic energy of the projectile would be very poor. Numerous additional computer simulations have since shown this to be the case for the conditions outlined in the published papers. 
     As a result, many low power railguns are constructed using dielectric materials to mechanically constrain the rails. Many of these railguns have been used for test purposes with modest currents where rail containment with dielectric materials alone is feasible. For very powerful railguns operating at mega-ampere levels, however, some amount of rail containment using metals is required, as the tensile strength of dielectric materials is too low to adequately constrain the rails by themselves. Typically, the metal used for these guns is high strength steel. The use of some amount of metal in the confinement structure is possible, as has been shown by extensive work by the University of Texas (Reference 3) that if there is no electrical conduction of the confinement vessel along the gun bore axis, metal constraints can be used. These metal constraints conduct current in the circumferential direction only. In this case, a series of metal rings are placed around the rails from one end of the rail gun to the other. Each of the rings is electrically insulated from the other with use of electrical insulators between each pair of metal rings. Use of a large number of such steel rings can result in an effective means to prevent the rails from expanding in the lateral direction during the armature launch. This is described in Reference 3. 
     However, and because the remainder of the railgun containment is constructed of dielectrics, there remains a serious problem of gun barrel droop. The current-carrying high voltage rails must be made of a highly conductive material such as copper, or more commonly a copper alloy, and cannot contribute to railgun stiffness along the bore axis, because copper is a relatively soft and ductile metal. Dielectric materials generally have insufficient tensile strength to produce railgun stiffness for a long gun bore. Therefore, the gun barrel must be made relatively short. As a consequence of this and to achieve a desired exit velocity for the projectile, the acceleration rate is correspondingly increased, which severely burdens other railgun systems, such as the electrical power source and the rails, given the commensurately higher rail currents that are now required. In addition, in pulsed mode of railgun powering, there remains considerable uncertainty that the remaining dielectric materials will have the reliability and lifetime to provide a practical solution, especially given that these materials are used in tension. 
     The parent U.S utility patent application, entitled “Railgun System”, focuses on lowering the sliding contact resistance between the armature and the rail of an electromagnetic railgun, using thermal energy to break apart the surface aluminum oxide layer residing on the rail surface. The armature nominally makes light mechanical surface contact with the rail surface so as to minimize rail surface damage due to gouging. The back armature surface is made flat for this purpose. 
     In said parent patent application, a second set of mechanical guide rails is used for guiding the armature and projectile. However, these guide rails are embedded into the surrounding dielectric material. Dielectric material is relatively weak mechanically and is limited in its ability to support these mechanical guide rails for a large number of launches without degradation of the underlying dielectric material. 
     The present invention remedies these and other problems associated with the prior art. 
     DISCLOSURE OF INVENTION 
     An electromagnetic railgun ( 10 ) comprising at least two elongated high voltage rails ( 11 ), a sliding armature ( 50 ) making electrical contact with each high voltage rail ( 11 ), at least two elongated metal support beams ( 14 ) adapted to provide mechanical strength to the railgun ( 10 ), said support beams ( 14 ) being substantially parallel to the high voltage rails ( 11 ), and a plurality of electrically conductive support plates ( 30 ) aligned circumferentially around the support beams ( 14 ) and along the length of the railgun ( 10 ), said support plates ( 30 ) adapted to provide additional mechanical strength to the railgun ( 10 ); wherein the support plates ( 30 ) are electrically isolated from each other and from the support beams ( 14 ). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other more detailed and specific objects and features of the present invention are more fully disclosed in the following specification, reference being had to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of an electromagnetic railgun  10  of the present invention. 
         FIG. 2  is a perspective view of the railgun  10  of  FIG. 1  showing a removable set of components comprising a high voltage rail  11 , an electrical insulator  12 , and a backing plate  13 . 
         FIG. 3   a  is an embodiment of the present invention showing circumferential confinement plates  30 . 
         FIG. 3   b  illustrates a single confinement plate  30 . 
         FIG. 4  illustrates further detail of a confinement plate  30 . 
         FIG. 5  is a perspective view of an embodiment of the present invention showing armature  50  positioned in a pair of guide rails  15 . 
         FIG. 6  is a perspective view of an embodiment of the present invention showing lubrication receptacles  16  and a convex curvature of a high voltage rail  11 . 
         FIG. 7  is a perspective view of an armature  50  suitable for use in the present invention. 
         FIG. 8  is a perspective view of an embodiment of the present invention comprising a tapered support beam  84 . 
         FIG. 9  is a perspective view of a railgun  10  of the present invention mounted onto a base  20 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The railgun  10  comprises a breech  17 , a muzzle  19 , and a bore  18 . An armature  50  propels a projectile (not illustrated) along the gun bore  18  between high voltage rails  11 . There is a support beam  14  associated with each high voltage rail  11 . A two-rail  11  system is illustrated herein, but this invention is not limited to two-rail  11  systems; any discrete number of rails  11  greater than or equal to two can be used. Each support beam  14  is proximate the back (outside) of each high voltage rail  11 , as shown in  FIG. 1 . 
     Each high voltage rail  11  is electrically isolated from its respective support beam  14  by being mounted onto an electrical insulator  12 . Preferably, the electrical insulator  12  is made of a ceramic material. Insulator  12  can generally be any electrical insulator operable up to approximately 30 kV that is also mechanically robust, such as G 10 . Each electrical insulator  12  can be directly attached to a corresponding support beam  14 . Preferably, however, each high voltage rail  11  and its associated electrical insulator  12  are together attached to a high strength (typically steel) backing plate  13 . In this preferred embodiment, the backing plate  13  is then attached to the support beam  14 , thus advantageously making it possible for the assembly  11 ,  12 ,  13  to be removable from the support beam  14  for maintenance or replacement of the high voltage rail  11 . This embodiment is shown in  FIG. 2 . In either embodiment, the electrical insulator  12  is under compression during all states of operation of the railgun  10 . 
     Each support beam  14  is made from metal, preferably high strength steel. Tensile strength in the approximate range of 800 MPa is desirable. While tensile strengths as high as 1600 MPa are possible, steels with such high tensile strength are typically used for cutting tools, and are not useful for this application. High strength steels with yield strength of approximately 800 MPa retain sufficient flexibility for this application. 
     For smaller and lighter weight railguns  10 , titanium is the preferred metal for the support beams  14 , backing plate  13 , and confinement plates  30  (see  FIG. 3   a ). The yield strength of titanium is approximately 50% that of steel. 
     The support beams  14  are placed proximate the rails  11  and extend along the full length of the railgun bore  18  from the breech  17  to the muzzle  19 . 
     The support beams  14  are physically attached to the gun base  20  (see  FIG. 9 ), which can be a turret or other mounting structure, but are not electrically grounded to the base  20 . The support beams  14  are not electrically connected to each other. Similarly, the backing plates  13  are not electrically connected to the base  20 , nor are they electrically connected to each other. The electrical insulation of the support beams  14  with respect to the rails  11 ; the electrical insulation of the support beams  14  with respect to the confinement plates  30 ; the electrical isolation of the support beams  14  with respect to each other and to the base  20 ; and the electrical insulation of the confinement plates  30  with respect to each other and to other parts of the railgun  10  allow for the railgun  10  to be fully enclosed in a confinement system made of metal (preferably steel), and to remain fully functional, with high electric to kinetic energy and power conversion efficiency. 
     Though in electrical isolation with respect to the high voltage rails  11 , the support beams  14  make a secure mechanical confinement to the rails  11  all along the length of the gun bore  18 . A primary purpose of the support beams  14  is to maintain planarity and parallelism between the rails  11  over the full length of bore  18 . In this way, the bore  18  length can be extended compared with what is possible with the prior art. 
     The Figures illustrate a preferred open architecture in which the support beams  14  do not form a continuous electrical path circumferentially at any point along the bore  18 . To maintain a high electric to kinetic energy and power conversion efficiency, it is preferred that the open architecture defined by the support beams  14  generally approximates that of the high voltage rails  11 , as is shown in  FIG. 1 . In other words, the openings between the support beams  14  are proximate the openings between the rails  11 . 
     On occasion and with enclosed gun bores of the prior art, a plasma arc will strike just behind the moving armature. It is generally assumed that the fast acceleration of the tight fitting armature around the gun bore and the creation of a partial vacuum in part create conditions for plasma arc formation. Because this is a lower impedance path than that of the armature, the arc superheats the surrounding gas and produces a pressure burst that can fracture the dielectric containment vessel walls of such existing railgun designs. In this embodiment of the present invention, on the other hand, the gun bore  18  is open to the atmosphere, thus preventing the formation of a partial vacuum behind the armature  50 . Should a plasma arc form, any over-pressure is immediately vented to the atmosphere through the large openings in bore  18  all along its length. 
     While being substantial in size and strength, the support beams  14  may be insufficient by themselves to keep the high voltage rails  11  from being forced apart during normal operation of the railgun  10 . In many applications, the force of repulsion between the two high voltage rails (e.g., when the current flow is in the mega-ampere range) deflects the support beams  14  away from each other to the point of permanent damage unless there are additional mechanical restraints. Shown in  FIG. 3   a  are several circumferential confinement plates  30  encircling the assembly comprising the support beams  14 , rails  11 , and insulators  12 . A number of the confinement plates  30  have been removed from railgun  10  in  FIG. 3   a  to more clearly show detail. One plate  30  is called out for detail in  FIG. 3   b . The confinement plates  30  keep the support beams  14 , and therefore the high voltage rails  11 , in place during an armature  50  and projectile launch. 
     Each confinement plate  30  consists of a continuous plate of metal (preferably steel) cut out in the center, with an insulator  32  fitted continuously along the inner surface of the cutout. This is shown in the detail of  FIGS. 3   a  and  4 . The confinement plates  30  are electrically insulated from all other electrically conductive parts  11 ,  14 ,  15  in the railgun  10 . Insulator  32  is preferably ceramic, is under compression, and makes physical contact with other parts  14  of the rail assembly  10 . While the Figures show the confinement plates  30  as having a non-square rectangular shape, other geometries, such as square, circular or elliptical, can be used. 
     The plate  30  thickness should be a small fraction of the plate  30  height and width. Also, the confinement plates  30  should be spaced apart sufficiently that the plate  30  thickness is a small fraction of the distance between adjacent plates  30 . Both requirements are to insure that the confinement plates  30  interfere only slightly with the magnetic field lines generated by the flow of current down one rail  11  and back along the other rail  11 . This is to insure that the inductance, and more precisely the inductance per unit length of the current flow in the high voltage rails  11 , not be significantly reduced. As the volume defined by the space between any two confinement plates  30  becomes a smaller fraction of the volume occupied by any one of the confinement plates  30 , the high voltage rail  11  inductance per unit length (L′) becomes smaller. The metric L′ is a key parameter for defining the conversion efficiency of electrical energy from the power generator to kinetic energy in the armature  50  and its associated projectile; Reference 4. 
     At the same time, the confinement plates  30  must do their part to hold the support beams  14  and high voltage rails  11  in place during the armature  50  and projectile launch. Therefore, the cross-section of the support plates  30  cannot be arbitrarily small. For example, consider the railgun under development by the United States Navy; Reference 5. This represents a particularly powerful railgun and is thus an extreme example. In this case, the requirement is to launch a projectile using approximately 6 mega-amps of current. Using a commercially available computer code (Reference 6) for calculating the magnetic fields for a given rail  11  geometry, and using a set of high voltage rails  11  that are 30 cm high and 30 cm apart, the confinement plates  30  must be able to counter an expansion force of 1.9×10 7  Newtons/meter, which is the amount of force exerted on the rail  11  per meter of length along the axis of the gun bore  18 . This is equivalent to 1.1×10 2  kilo-pounds/in 2  per inch along the length of the gun bore  18 . Assuming an inter-support plate  30  spacing of 12 inches, each steel support plate  30  must support 1.1×10 2  kpsi×12=1.32×10 3  kpsi. For high strength steel with a yield strength of 800 MPa, or approximately 120 kilo-pounds/in 2  (kpsi), applying a factor of 2× for safety (i.e., using 400 MPa or 60 kpsi) results in a required cross-sectional area of 2.2×10 1  in 2  or 1.42×10 2  cm 2 . The confinement plate  30  has an upper and lower side to confine the expansion force, so that the plate  30  cross-section need be only of this result, or 70 cm 2 . A plate  30  width of 2 cm and height of 10 cm more than suffices to meet this confinement requirement. A 2 cm thick plate  30  with an inter-plate spacing of 30 cm represents a filling factor of approximately 7%. Therefore, the reduction in the inductance should be no worse than this amount. In fact, it is considerably less than this, as the magnetic flux is determined primarily by the volume between the two high voltage rails  11 , and the flux is for the most part diverted around these confinement plates  30 . 
     While Reference 3 shows confinement rings, what has not been appreciated prior to this invention is the great advantage of using a longitudinal support beam  14  in conjunction with circumferential confinement plates  30 , under the appropriate operating conditions. It has been widely believed in the field for approximately 25 years that the use of metal conductors that confine the high voltage rails  11  in both the longitudinal and circumferential directions simultaneously would result in poor electrical efficiency. Leading lines of research continue with development of confinement rings only (Reference 7), which continues to teach away from the present invention. Therefore, practitioners in the art have used metal confinement devices in the circumferential direction only to address the serious problem of high voltage rail repulsion. The issue of gun bore droop has been tentatively resolved by designing railguns with short bore lengths and accommodating for this with sometimes exceedingly demanding requirements in other parts of the railgun system. 
     The reason that practitioners believed that support beams  14  and confinement plates  30  could not be used together was the result of the previously-cited theoretical papers published in the scientific literature in the mid-1980s; References 1 and 2. These papers taught, and rightly so, that a single electrically conducting confinement tube brought into close proximity to the high voltage rails of a railgun would result in a railgun of poor electrical efficiency. What was shown in these papers and with detailed mathematics was that it was the combination of the confinement tube&#39;s electrical conductivity in the circumferential direction together with its simultaneous conductivity in the longitudinal direction that leads to the poor efficiency. 
     What was not recognized until this invention, however, was that: (1) by separating the electrical conductivity in the circumferential direction from that in the longitudinal direction using a mechanical confinement structure  30 ,  14  made of metal, (2) by insuring that each element  30 ,  14  of the confinement structure be electrically isolated from each other element  30 ,  14 , and (3) by introducing into the confinement structure large open gaps between adjacent confinement plates  30  in conjunction with a wide gap in both the top and bottom regions between the support beams  14  to allow for unimpeded passage of the magnetic flux generated from the high voltage rail  11  current to pass, a full metal enclosure of the railgun  10  can be accomplished in a highly efficient and elegant manner. 
     Guide Rails  15   
     Practitioners in the art have reported substantial problems with vibration of the armature during acceleration. This is understandable, as acceleration to supersonic velocities for this application is often required. Today, all railguns are designed so that high voltage rails are used to conduct current across the armature while simultaneously acting as mechanical guide rails for the armature and projectile. The present invention recognizes that it is easier to suppress vibrations when the weight and guidance of the armature  50  and projectile are carried on separate rails  15  from those  11  of the electric power flow to and from the armature  50 . 
     In this invention, the support beams  14  are placed just behind their associated high voltage rails  11 , and by judicious design serve the dual function of mechanical support for the high voltage rails  11  and mechanical guides for the armature  50  and projectile. This is shown in  FIG. 5 . The guide rails  15  are used to support the weight of the armature  50  and the projectile, and to guide the armature  50  and the projectile down the gun bore  18  during launch. Each high voltage rail  11  is used to supply current to and from the conducting plate  73  portion of the armature  50 . 
     The weight bearing rails  15 , which are typically made of steel, are designed for weight loading and wear resistance. In this invention, these two functions are separated and optimized by the different types of rails  11 ,  15 . To further minimize the potential for vibration, each mechanical rail  15  can be integrated directly into the support beam  14 , as shown in  FIG. 5 . Alternatively, each mechanical rail  15  can be a separate entity attached to a support beam  14 . Instead of making direct contact, one or more armature attachments  74  can ride on a fluid or gas layer between the attachment  74  and its respective guide rail  15 . 
     Convex High Voltage Rails  11   
     Shown in  FIG. 6  is an example of a high voltage rail  11  with a convex curve on its front surface (i.e., the surface facing armature  50 ). Practitioners in the art today employ either flat or concave curvatures only. Flat high voltage rails have been used extensively for research purposes at low power where mechanical guidance has not been of primary concern. At high power and velocity, concave rail cross sections have been employed to aid in armature mechanical support and guidance in the gun bore. However, this runs counter to the magnetic field shaping that is natural to the railgun  10 . Near the edges of the rails for the concave rail-type gun are flux line concentrations, which are the result of surface current concentrations at the high voltage rail edges. As a result of this excessive rail edge heating, deformation and early rail wearout occur. 
     The present invention preferably uses high voltage rails  11  having a convex front surface, i.e., the surface making contact with armature  50 , so that the surface current density near the rail  11  edge can be managed more easily. By adjusting the radius of curvature, which can vary from center to edge while overall being convex, the surface current density can be managed quite well. 
     Lubrication Receptacles  16   
     Also shown in  FIG. 6  are lubrication receptacles  16 . Preferably, receptacles  16  are part of a removable backing plate  13 , and therefore easily removable along with the high voltage rail  11 . Receptacles  16  can be located on both sides of a rail  11 , and capture a lubricant, such as liquid aluminum, that is produced at the sliding electrical contact  73 , which is preferably made from aluminum alloy. Each receptacle  16  preferably extends from the breech  17  to the muzzle  19 , and is part of the backing plate  13  itself. The receptacle  16  typically contains a material with enhanced surface area to volume ratio. Such an architecture can efficiently collect, trap, and hold the incident lubricant after it has solidified. Preferably, the material comprising receptacle  16  is a honeycomb of steel or stainless steel with a highly roughened surface which is replaceable within the receptacle  16 . In operation of the railgun  10 , hot liquid aluminum or another lubricant is jetted at generally right angles to the direction of armature  50  motion along the sliding contact  73  region. The lubrication receptacles  16  are designed in conjunction with the convex nature of the high voltage rails  11 , so that the jetted lubrication is incident on the openings of the receptacle  16 . 
     As is shown in  FIG. 6 , the receptacle  16  is designed with a large number of cells. Preferably, each cell has cell walls that come to a sharp edge at the forwardmost point of the cell, i.e., the part of the cell closest to the muzzle  19 . 
     These receptacles  16  serve the same purpose as the liquid aluminum sump described in the parent patent applications. 
     In a preferred embodiment, the materials in receptacles  16  are designed with a large surface area to be able to hold a large amount of solidified aluminum before need of replacement. The knife edge design of the forwardmost edges is designed to prevent backsplash of the incident liquid aluminum. The materials in the receptacles  16  are made as separate parts to the backing plate  13  and fabricated into sections so as to accommodate thermal expansion and contraction effects. 
     Armature  50  Design 
       FIG. 7  shows a perspective view of the armature  50 . There are three layers to the armature  50 . The first, which is forward-most (closest to the muzzle  19 ), is the armature base  71 . This part is preferably made of steel. The armature base  71  is connected to a set of armature attachments  74 . Just behind the armature base  71  and mechanically attached thereto is a continuous plate  72  of electrically insulating material. Preferably, this material is ceramic, and is under compression. The electrically insulating plate  72  insures that all of the current from one high voltage rail  11  is conducted solely to the second high voltage rail  11 . The third layer (which faces the breech  17 ) is a low resistivity electrically conducting plate  73  that conducts current from one high voltage rail  11  to the other  11  as the armature  50  slides along the bore  18 . This plate  73  is preferably made of aluminum or aluminum alloy, and is electrically insulated from all parts in the railgun  10  except for the high voltage rails  11 . 
     Preferably, armature  50  has at least one attachment  74  on each side that fits into a guide rail  15 . Each attachment  74  makes sliding contact with at least part of its respective guide rail  15  surface. The attachment  74  can ride on a fluid or gas layer between the attachment  74  and the guide rail  15 . Attachments  74  are mechanically secured to the remainder of the armature  50 , but electrically insulated from the armature base  71  by means of insulators  75 . 
     Tapered Railgun  80   
     In the embodiment of this invention illustrated in  FIG. 8 , the support beams  84  are tapered from the breech  81  to the muzzle  82 , with the widest portions of the tapered support beams  84  at the breech  81 . In this embodiment, each of the confinement plates  30  is replaced with a pair of external clamps  88  that are independent of each other. Each clamp  88  is electrically insulated from the tapered support beams  84 , from all other clamps  88 , and from every other metal part in the railgun  80 . At the inner edges of each clamp  88  is an electrical insulator (not illustrated) which makes physical contact with the tapered support beams  84 . The preferred material for the electrical insulator is ceramic, and the electrical insulator is under compression. 
     When the support beams  84  are cantilevered at the gun base  81 , the gun  80  length can be extended further, compared with a non-cantilevered design. This can be of further benefit in lengthening the gun barrel (bore)  83  and being able to either achieve a higher exit velocity for the projectile for a given set of input parameters, or, alternatively, to be able to reduce the input parameters to achieve a fixed output specification. 
     Due to the extension of metal from the support beam  84  further from the rail  11 , the inductance per unit length (L′) varies along the length of the gun  80 . L′ is lowest near the gun breech  81  and is highest near the muzzle  82 . With all else, and especially the drive current, being held fixed, the armature  50  acceleration continues to increase along the gun barrel  83  with the tapered design. 
     Base  20   
       FIG. 9  illustrates railgun  10  mounted on a support base  20 , and shows that the support beams  14  (including their extensions  94 ) are insulated from all of the metal (usually steel) components  91 ,  92 ,  96 ,  97 ,  98  of base  20 . 
     In this embodiment, support beams  14  are extended in a horizontal direction near the breech  17 , forming extended support beams  94 , which provide additional mechanical support. In this embodiment, base  20  is a pivoting turret, but other types of bases  20 , such as fixed bases and shoulder mounted bases, can be employed. In this illustrated embodiment, a fixed portion  98  of the base is mounted to a surface of a ship, tank, or other large object. Wheels  97  allow railgun  10  to pivot with respect to the fixed portion  98 . Top brackets  91  and top plates  92  are used to mechanically secure extended support beams  94  to the breech  17  end of turret  20  via insulators  93 . Similarly, insulators  95  electrically isolate support beams  14 ,  94  from the railgun portion  96  of turret  20 . Railgun portion  96  provides additional mechanical support. 
     Insulators  93 ,  95  are preferably fabricated of ceramic, and are under compression. Ceramic, including fracture toughened ceramic, has a compressive strength of around 2,100 to 2,400 Mpa, as noted in various engineering journals. As noted previously, the tensile strength of steel is typically quoted as around 800 Mpa. Therefore, there is a need for approximately 40% less ceramic area  95  under compression than the cross-sectional area of the support beams  14  under tension. A considerable engineering margin, by several factors, has thus been incorporated in the embodiment illustrated in  FIG. 9 . 
     Steel bolts (not illustrated) within each top bracket  91  can be run through the adjacent ceramic insulator  93  and directly into the adjacent steel extended support beam  94  In extended support beam  94 , the bolt can be run through an insulated hole, which is typically lined with ceramic, and terminated with a set of steel and ceramic washers. In this way, there is no direct electrical path through the bolt from one set of steel parts  91 ,  92  to another  94 . In this embodiment, the ceramic washers are under compression. 
     The above description is included to illustrate the operation of the preferred embodiments, and is not meant to limit the scope of the invention. The scope of the invention is to be limited only by the following claims. From the above discussion, many variations will be apparent to one skilled in the art that would yet be encompassed by the spirit and scope of the prevent invention.