DC powered hybrid coil gun employing superconducting elements

A device and apparatus, consisting of a standard barrel, a superconductive magnet winding wrapped around the barrel, a large mass piston and a projectile. This device is a direct-current powered hybrid coil gun which operates to accelerate projectiles to high velocity without the requirement of gigawatt power pulses. The device also lowers the cost of power required per shot and makes possible extended life of the individual parts of the apparatus.

FIELD OF THE INVENTION 
My present invention relates to direct-current powered hybrid coil guns 
employing superconducting coils, and to a method of operating same. 
BACKGROUND OF THE INVENTION 
The history of guns and projectiles dates back at least several thousand 
years to the original discovery of gunpowder in China. Gunpowder is 
essentially a mixture of solid chemicals comprised of an oxidizing agent 
plus reducing agents capable of being oxidized. If gunpowder is confined 
in a small space in conjunction with a projectile, i.e. a "bullet", and is 
then detonated, chemical energy changes the solids to hot gases almost 
instantaneously, and the chemical energy is converted to kinetic energy, 
causing the projectile to accelerate. 
In yet another version of a gun, the projectile is accelerated by the use 
of coils situated on a barrel in such a manner that the the coils can be 
energized in turn to produce an electromagnetic field and thereby 
accelerate the the projectile. 
Electromagnetic and coil guns of prior art designs require gigawatt 
electric power supplies to operate. The weight and the complexity of these 
power supplies severely limits the potential use of these guns. It is 
prohibitive to use these guns for systems which require low weight such as 
space borne weapons or mobile systems. 
The development of electromagnetic guns has also been hindered by the 
factor of severe rail erosion. It is not clear after many year of 
development whether such problems can be overcome. The most advanced rails 
developed to date are limited to a few shots. Yet weapon systems employing 
electromagnetic and coil guns require that at least a few hundred shots be 
delivered without barrel replacement to be satisfactory. 
OBJECTS OF THE INVENTION 
It is an object of the invention to provide an improved electromagnetic gun 
which eliminates the need for a gigawatt power supply. 
I have also to provide a system in which barrel erosion and rail damage is 
considerably lessened and/or nearly completely eliminated, so much so that 
the usage of said electromagnetic and coil guns become feasible as a 
weapon system. 
It is a further object to provide a coil gun which does not require the 
usage of inordinate amounts of powder. 
SUMMARY OF THE INVENTION 
These objects are attained in accordance with the invention in a hybrid 
coil gun which comprises: 
a projectile formed with at least one closed-loop electromagnet winding; 
a piston formed with at least one closed-loop electromagnet winding; 
means defining at least one barrel receiving the projectile and from which 
the projectile can be electromagnetically propelled; 
coil means on the barrel having at least a portion magnetically coupling to 
the closed-loop winding of the projectile for magnetically propelling the 
projectile from the barrel, the coil means comprising a closed-loop 
portion generating an external field and magnetically coupling to the 
closed-loop winding of the piston to decelerate the piston and generate by 
induction a current pulse for magnetically propelling the projectile; and 
means for applying a chemical propellant to the piston to drive the piston 
through the closed-loop portion of the coil means and the external field, 
whereby the current pulse is induced, the closed-loop portion generating 
an external field of axially tapering field strength. 
The discovery of high critical temperature ceramic compositions having 
superconducting properties is of recent origin. Originally, 
superconductivity was observed in mercury at 4 K. by the Dutch scientist, 
Heike Onnes. 
The term, superconductivity, refers to the property wherein a normally 
resistive conductor abruptly loses all resistance to electrical flow at a 
specific temperature to, called the critical temperature T.sub.c. At this 
point, the resistivity of the normal conductor becomes zero, and to 
conductor becomes superconducting. In more recent times, niobium metal 
alloys have been used in superconducting coils at temperatures up to 23 K. 
It had previously been believed that superconductivity above 23 K. was not 
possible. This belief was based on the theoretical work of Bardeen, Cooper 
and Schieffer (BCS theory-1946) which predicted such a limit. Several 
theoretical proposals were presented in the 1970's, suggesting that the 
critical temperature for superconductivity could be increased. However, 
the lack of any early discoveries of superconductivity above 23 K. 
solidified the belief that indeed this temperature could not be exceeded. 
Thus, in November, 1987, when Bednorz and Muller announced the discovery of 
a new ceramic superconducting compound based on lanthanum, barium, and 
copper oxides, whose critical temperature for superconductivity was close 
to 35 K., (G. Bednorz and A. Muller, Z. Phys., B64 189 (1986)), the 
declaration was greeted with considerable scepticism. Nevertheless, by the 
following month, the critical temperature T.sub.c, for the onset of 
superconductivity was raised to nearly 80 K. by C.W. Chu and coworkers (M. 
K. Wu, J.R. Ashburn, C.J. Tang, P.H. Hor, R.L. Meng, L. Gao, Z. J. Huang, 
Y. Q. Wang and C. W. Chu, Phys. Rev. Lett. 58 908 (1987)). This was 
achieved by changing the composition to yttrium barium copper oxide, 
approximated by the formula: 
EQU Y.sub.1.0 Ba.sub.1.8 Cu.sub.3.0 O.sub.6.3 
This formula, determined experimentally, is not exactly stoichiometric. It 
is believed that this lack of specific nonstoichiometry contributes most 
to the onset of superconductivity. The so-called 1:2:3 compound, composed 
of Y-Ba-Cu-O atoms, is prepared by the solid state reaction of the 
requisite oxides, vis: 
EQU Y.sub.2 O.sub.3 +2BaO+3 CuO=2 YBa.sub.2 Cu.sub.3 O.sub.6.5. 
It is now established (C.N.Rao et al, Nature, 327 185 (1987)) that high 
T.sub.c superconductivity in the Y-Ba-Cu-O system originates from a 
compound of stoichiometry: YBa.sub.2 Cu.sub.3 O.sub.7- , where " " is a 
value less than 1.0. This compound has the structure of the ideal 
perovskite, YBa.sub.2 Cu.sub.3 O.sub.9. Thus, the superconductor YBa.sub.2 
Cu.sub.3 O.sub.7- has about 25% fewer oxygen atoms present in the lattice 
as compared to the idealized cubic perovskite structure. This massive 
oxygen deficiency means that instead of the conventional three-dimensional 
crystalline cubic-stacking array of the perovskite, a unique layered 
structure results. A loss of even more oxygen atoms in this structure 
gives rise to the semiconductor YBa.sub.2 Cu.sub.3 O.sub.6. The chain of 
copper atoms associated with a chain of oxygen atoms is believed to be the 
key to superconducting behavior. Yet the above description is an idealized 
one and the actual distinct structural conformation has not yet been 
delineated. Note that there appear to be extra oxygen atoms in the 
superconducting unit cell, compared to that of the semiconductor. 
To date, most of the high-T.sub.c superconducting ceramic compositions 
announced to date are based on cuprate compounds having Cu-O.sub.2 layers 
as part of the structure. Some of these have included: 
Bismuth Strontium Calcium Copper Oxide : 
______________________________________ 
Bi.sub.2 Sr.sub.3-x Ca.sub.x Cu.sub.2 O .sub.8+y 
T.sub.c = 114 K. 
______________________________________ 
Thallium Calcium (Barium) Copper Oxide: 
______________________________________ 
T1 Ba.sub.2 Ca Cu.sub.2 O.sub.7 
T1 Ba.sub.2 Ca.sub.2 Cu.sub.3 O.sub.9 
T1 Ba.sub.2 Ca.sub.3 Cu.sub.4 O.sub.11 
T1 Ba.sub.2 Ca.sub.4 Cu.sub.5 O.sub.13 
T.sub.c = 120 K. 
______________________________________ 
Lead Strontium Lanthanide Copper Oxide 
______________________________________ 
Pb.sub.2 Sr.sub.2 (Nd.sub.0.76 Sr.sub.0.24)Cu.sub.3 O.sub.8+x 
T.sub.c = 77 K. 
______________________________________ 
In the last compound given, the CuO.sub.2 - sheets are present but there is 
also a PbO-Cu-OPb sandwich as well, not observed in ceramic 
superconductors prior thereto. The copper ions in this sandwich are 
monovalent and each is coordinated, above and below, to two oxygen atoms 
in the PbO layers. The copper atoms in the CuO.sub.2 sheets have an 
average valence of about 2.25, which is consistent with previously 
discovered cuprate compounds, given above. However, the presence of 
Cu.sup.+ atoms lowers the average valence of copper ions in the new 
structure to below 2.0, which is atypical. Indeed, preparation conditions 
needed to prepare these compounds includes a mildly reducing atmosphere so 
as not to oxidize Pb.sup.2+ to Pb.sup.4+. 
There have also been some compositions announced, based on a copper-free 
composition, vis: 
EQU BaO- K.sub.2 O - Bi.sub.2 O.sub.3 
This compound is said to become superconducting at about 30 K. While 
copper-oxide superconductors exhibit layered structures that carry current 
efficiently only along certain planes, this new material is a 
three-dimensional network of bismuth and oxygen with properties that are 
much less sensitive to crystallographic direction. It is hoped that 
compositions will be discovered in this system with temperature properties 
that rival those of copper-bearing compounds. 
The main advantage to superconducting compositions with higher T.sub.c 
values is that they can operate at liquid nitrogen temperatures (78 K.), 
thus avoiding the need to use liquid helium. Superconducting ceramic 
compositions are normally prepared by weighing out specific quantities of 
selected oxides. The combination is thoroughly mixed by conventional means 
and then fired at elevated temperatures above about 950 C. The induced 
solid state reaction causes the formation of the desired ceramic 
composition and structure. Further annealing in an oxygen atmosphere has 
been found to improve the superconducting properties of the Y-Ba-Cu-O 
compound. The produced powder is then processed by conventional means to 
form a bar (by compaction) which is then used as the superconducting 
medium. 
I have found that my new invention employing high critical temperature 
superconducting ceramics to form the superconducting coils of the instant 
invention eliminates many of the problems associated with the design of 
electromagnetic and coil guns of the prior art. 
The DC powered hybrid coil gun consists of a standard barrel, a magnet 
winding wrapped around the barrel, a large mass piston and a projectile. A 
conventional gun can be modified to operate as a direct-current powered 
hybrid-coil gun to accelerate projectiles to high velocities and 
frequencies which cannot otherwise be achieved. The gun arrangement of the 
instant invention facilitates collision between the large mass piston and 
a small mass projectile, thereby resulting in velocity amplification. Said 
collision is accomplished through the magnetic field interaction between 
the piston and an external field, between the projectile and the external 
winding, and between the piston and the projectile. The use of high 
critical temperature superconducting coils eliminates the need for using 
liquid helium. The external field is charged prior to firing of the gun, 
using a DC power supply. The external field decay during firing has been 
found to be negligible and multiple shots can be fired, facilitated by the 
presence of the superconductive external field winding. 
The main components of the direct-current powered hybrid-coil gun are: the 
gun barrel, the external magnet windings, the piston, and the projectile. 
The barrel has a standard conventional winding which is tapered in the 
combustion region. It is only subject to gaseous pressure and not to 
magnetic forces. The barrel wall can thus be made thin if the gaseous 
pressure is reduced. 
The magnet design consists of a selected superconducting winding which 
produces an axially tapered field. It can be made from conducting 
materials such as metals, coated with a selected superconductor. Low 
current and low voltage is acceptable to charge the magnet if charging is 
done over a sufficiently long time. 
The piston has a conductive winding which is thermally insulated from the 
high temperature combustion products. This can be achieved by embedding a 
metallic winding in a ceramic matrix. The piston also has a conductive 
windings and requires no insulation since it is not in contact with the 
combustion products. 
Propellants or explosives are used to power the gun and the following 
sequence of events takes place during operation: 
(a) The piston is accelerated by the high pressure gas generated in the 
barrel. 
(b) The piston, reaching a certain velocity, approaches the external 
solenoid region. The piston is thus subjected to a positive field gradient 
and is thus subject to a decelerating magnetic force. 
(c) Current is induced in the piston windings as it moves in the external 
magnetic field. Initially, the current in the piston will be in the 
opposite direction to the current in the external windings. The external 
magnet current also increases. 
(d) The increase in the solenoid current induces current in the projectile 
windings. The projectile is placed in a low field gradient region near the 
center of the magnet windings, so as to have sufficient time for charging 
its coil. 
(e) The currents induced in the piston and the projectile windings are 
initially in the same direction. The current in the external winding flows 
in the opposite direction. 
(f) The projectile is initially placed in a negative field gradient 
producing accelerating magnetic forces. 
The operation described above is equivalent to the collision of two objects 
and is defined here as magnetic collision. This will result in velocity 
multiplication and projectile velocities in excess of 4 km/s. Such system 
is also suitable for space launching. 
The application of high critical temperature superconductors makes the use 
of the direct-current powered hybrid-coil gun of my new invention 
practical since no liquid helium will be required. It is preferred, but 
not necessary, to use a superconducting winding for the piston, and/or the 
projectile, since they carry current for a short time. 
In the operation of my new invention, current in the piston windings 
decreases as the piston moves away from the positive field gradient region 
into the negative field gradient region. The piston is first accelerated 
and is then decelerated as the current reverses. A switch is opened when 
the velocity reaches zero so that said piston can be retrieved and 
repetitively used. 
Simultaneous multiple firing is also possible . The external solenoid 
winding decelerating the piston is used to charge a number of solenoids. 
These solenoids are used to simultaneously accelerate the multiple 
projectiles.

SPECIFIC DESCRIPTION 
FIG. 1 shows a hybrid coil gun according to the invention in which the 
barrel a of a nonmagnetic material which can be a ceramic or a metal 
having low magnetic susceptibility is surrounded by three coils d 
respectively represented at 1, 2 and 3 to generate, along the barrel a 
generally tapered field strength characteristic of the type shown in FIG. 
3A in which the field strength is plotted as a function of distance along 
the barrel. 
A projectile b is received within the barrel downstream from a propellant 
mass 4 which can be ignited by an igniter 5. In general, the mass 4 can be 
gun powder or the like ignited by a spark from the igniter 5, although any 
other selectively detonatable means for producing propellant gases can be 
used. 
Located specifically downstream of the midpoint of the field strength 
characteristic is a projectile c which can be magnetically propelled as 
will be described in greater detail hereinafter. The coils 1-3 can be 
energized by a direct-current source 6 which charges these coils. The 
coils are composed of wire, film, bands or the like of one of the 
high-temperature superconductive materials previously described. 
The portion receiving the coil means 1, 2, 3 can be enclosed in a chamber 7 
which can be supplied with nitrogen or some other coolant, e.g. from a 
tank 8, the latter representing cooling means for bringing the coil 
temperature to superconductivity temperature, i.e. a temperature below the 
critical temperature T.sub.c of the superconductor. The cooling means 7, 
of course, also serves to cool the piston b and the projectile c to the 
critical temperature T.sub.c of their respective superconductor windings 
described in connection with FIGS. 2A and 2B. 
The projectile can be, for example, a satellite to be launched by the 
motion into space or any other projectile. 
In operation, with the coil means 1, 2, 3 charged to create a magnetic 
field as shown in FIG. 3A, the firing of the propellant mass will generate 
propellant gases to drive the piston b to the right. The tapering magnetic 
field encountered by the coil of the winding of the piston induces a 
current flow therein and the resulting magnetic field induces a current 
pulse in the coil means which is superimposed upon the direct-current 
field thereof and induces a magnetic pulse which drives the projectile c 
to the right with amplified velocity and without, of course, any direct 
contact between the piston and the projectile. 
Switch means represented diagrammatically at 9 can be actuated to 
deenergize the coils 1-3 or to quench the superconductor, or field 
reversal may be generated to draw the piston b back into its original 
position for the firing of another projectile and a fresh mass of 
propellant material can be introduced through a breach in the barrel (now 
shown) or by any other means. 
As can be seen from FIG. 2A, the piston b can comprise a body (e.g. of 
ceramic) 10 formed with a closed-loop winding 11 composed of one of the 
high-temperature superconductors previously described whereas the 
projectile c of FIG. 2B is likewise composed of a body 12 (e.g. of 
ceramic) and a closed-loop superconductor winding 13. 
As can be seen from FIG. 4, the coil means need not comprise the coil 
assembly shown in FIG. 1 in which tapered fields tapered in opposite 
directions lie on opposite sides of a median plane, but can comprise 
spaced-apart coils. For example, here the barrel means is formed by two 
barrels 20 and 21, respectively receiving the piston b and the projectile 
c. 
The barrel 20 is surrounded by the coil 22 composed of a superconductor and 
series connected with a coil 23 surrounding the barrel 21 so that the 
current pulse generated by propellant of the piston is transmitted by 
conductors 24 to the coil 23 to propel the projectile. The means for 
charging the coils 22 and 23, namely, a direct-current source, and for 
cooling the gun to a temperature below the critical temperature T.sub.c of 
the superconductors may be the same as has been illustrated in FIG. 1. The 
downstream portion of the barrel faces in a direction opposite a direction 
in which the upstream portion faces and the upstream and downstream 
portions can be mechanically connected together to minimize recoil. 
The principle of FIG. 4 is also applicable to the firing of a plurality of 
projectiles. Here the barrel means comprises a piston barrel 30 and 
projectile barrels 31, 32. The piston b, driven by a propellant as 
previously described but not illustrated in this Figure, cooperates with 
the magnetic field of coil 33 to generate the current pulse which is 
applied by the conductors 34 and 35 to the coils 36 and 37, respectively, 
surrounding the barrel portions 31 and 32 to magnetically propel the 
projectile c within these barrels to the right. The closed-loop portion of 
the coil means is here connected electrically in parallel to a plurality 
of further windings on respective downstream portions of the means 
defining the barrel for propelling respective projectiles therefrom.