Cartridge containing plasma source for accelerating a projectile

A projectile is accelerated through a gun barrel bore by a cartridge containing a high temperature, high pressure plasma jet source. The cartridge has a geometry enabling it to be loaded into a breech bore of the gun. The plasma jet is supplied to the rear of the projectile and is derived by a tube having an interior wall forming a capillary passage. A discharge voltage applied between spaced regions along the capillary passage ionizes a dielectric to form a plasma. First and second ends of the passage are respectively open and blocked to enable and prevent the flow of plasma through them. The blocked end closes the breech bore.

RELATION TO CO-PENDING APPLICATION 
The present application is related to commonly assigned, co-pending 
application, Ser. No. 471,215, filed Mar. 1,1983, now U.S. Pat. No. 
4,590,842. 
TECHNICAL FIELD 
The present invention relates generally to guns and more particularly to a 
gun for receiving a cartridge that includes a capillary passage and a 
dielectric ionizable substance which, when ionized, supplies a high 
temperature, high pressure, plasma jet to the rear of a projectile in a 
barrel bore of the gun. 
BACKGROUND ART 
Presently used guns generally depend on high energy, high density 
exothermic, chemical propellants to provide high pressure gasses in a 
chamber and barrel to accelerate a projectile in the chamber through the 
barrel. Such guns are efficient reliable devices for projectile devices 
below about 1.5 kilometers per second. However, sound speed limitations of 
two phase mixtures incorporated in burning propellant grains and gasseous 
combustion products cause a rapid decline in gun efficiencies for higher 
projectile velocities. In the hypervelocity range, above 1.5 kilometers 
per second, it is desirable to use other energy sources to heat 
conveniently packaged low atomic weight propellants inside of a gun. It 
appears to be quite attractive to use an electrical source located outside 
of the gun to supply energy to heat the low atomic weight propellants 
inside of the gun. 
It is, accordingly, an object of the present invention to provide a new and 
improved apparatus for enabling a gun to accelerate projectiles 
efficiently to the hypervelocity range. 
Another object of the invention is to provide a new and improved 
hypervelocity gun that employs electrical energy generated outside of the 
gun to heat low atomic weight propellants located inside of the gun. 
DISCLOSURE OF INVENTION 
In accordance with one aspect of the present invention, a projectile is 
accelerated from a gun having a barrel with a bore adapted to receive the 
projectile and a breech block having a bore aligned with the barrel bore. 
A cartridge in the breech block bore includes means for supplying a high 
temperature high pressure plasma jet to the rear of the projectile in the 
barrel bore. The plasma jet source includes a tube having an interior wall 
forming a capillary passage. A discharge voltage is supplied by a suitable 
source between spaced regions along the length of the interior wall while 
a dielectric ionizable substance is between the regions. The dielectric 
ionizable substance includes at least one element that is ionized to form 
a plasma in response to the discharge voltage being applied between the 
spaced regions. The passage has a diametric length that is short relative 
to the distance between the spaced regions to form the capillary passage. 
First and second ends of the passage are respectively open and blocked to 
enable and prevent the flow of plasma through them. The blocked end closes 
the breech bore. The plasma forms an electric discharge channel between 
the spaced regions. Ohmic dissipation occurs in the electric discharge 
channel to produce a high pressure in the passage to cause the plasma in 
the passage to flow longitudinally in the passage through the first end to 
form the plasma jet which accelerates the projectile through the barrel 
bore. 
In the preferred embodiment, the interior wall of the tube forming the 
capillary passage is solid and includes the dielectric ionizable 
substance. The element is ablated and ionized from the solid to form the 
plasma. 
In the preferred embodiment, the voltage is supplied to the spaced regions 
by a first electrode forming the first end and a second electrode that 
plugs the second end. The first electrode extends longitudinally of the 
tube toward the gun barrel from adjacent the blocked breech end and abuts 
against an edge of the tube remote from the blocked breech end and 
adjacent the barrel bore. The second electrode comprises a metal plate 
positioned and mounted to block the breech bore. 
The capillary passage preferably includes an outwardly flared nozzle 
through which the jet is injected into the barrel so the jet expands, 
causing cooling of the jet as it enters the barrel. Thereby, the barrel is 
not subjected to the very high temperature plasma that is within the 
capillary passage, to preserve the barrel life. 
It is a further object of the invention to provide a cartridge adapted to 
be inserted into a gun breech bore, which cartridge includes a plasma 
source for supplying high pressure to a projectile in a barrel bore of the 
gun, to accelerate the projectile to the hypervelocity range. 
A further object of the invention is to provide a new and improved plasma 
source for accelerating projectiles in gun barrels, wherein the plasma 
source includes materials that dissociate into low atomic weight 
constituents thereby generating material with a high sound speed, so that 
the material flows rapidly out of a capillary tube in which it is located. 
A further object of the invention is to provide a reusable cartridge 
containing a plasma source capable of supplying a high pressure, high 
velocity jet to a projectile in a gun barrel, to accelerate the projectile 
to hypervelocities. 
It is preferable for the capillary geometry to have a relatively high 
resistance, such as one-tenth of an ohm. In such a situation, there is an 
efficient energy transfer by ohmic dissipation from a power supply into 
the plasma, which in turn streams out of the nozzle with a high velocity, 
directed flow. Simultaneously, plasma is replenished by radiative ablation 
of the dielectric wall confining the discharge, to maintain the jet. Such 
ohmic dissipation in the capillary discharge transfers energy from the 
electric energy source into the plasma with an efficiency approaching 
one-hundred percent since the capillary plasma discharge functions as a 
simple resistor in a circuit energized by the electric energy source. As 
plasma is ejected through the nozzle at the end of the tube remote from 
the end of the breech and adjacent the barrel bore the energy is 
partitioned between plasma pressure, dissociation, ionization energy, and 
streaming kinetic energy. In response to energy being coupled to the 
interior wall of the capillary passage, principally by radiation derived 
from the plasma, the dielectric is ablated from the wall. Thereby, 
additional plasma is added to the plasma originally formed by the 
discharge in the passage to assist in maintaining the discharge. The 
dielectric tube forming the capillary passage can be provided with 
ablatable large surface area fillers to increase the amount of plasma 
produced and increase the resistance of the electrical channel formed 
between the spaced regions. Typically, the filler is many small powder 
spheres together having a total surface area of 100 to 1000 times the 
surface area of the cylinder where the filler is located. Because the 
fillers have an inertial mass much greater than that of the plasma (e.g., 
100 times) the plasma quickly flows through the filler and is cooled 
thereby to assist in preventing ablation of the channel and gun barrel. 
Alternatively, the filler is water confined in a plastic bag. 
The above and still further objects, features and advantages of the present 
invention will become apparent upon consideration of the following 
detailed description of several specific embodiments thereof, especially 
when taken in conjunction with the accompanying drawing.

BEST MODE FOR CARRYING OUT THE INVENTION 
Reference is now made to FIG. 1 of the drawing wherein gun 11 is 
illustrated as including elongated barrel 12, containing rifled or smooth 
bore 13. Gun 11 includes a breech 14 in which is located cartridge 15. 
Cartridge 15 contains projectile or bullet 16. High voltage power supply 
17 selectively supplies high voltage, high current electric pulses by way 
of leads 19 and 20 to a plasma source in cartridge 15 when switch 121 is 
closed; typically the current and voltage are approximately a few hundred 
kiloamperes and a few tens of kilovolts. 
In response to the electric energy supplied to cartridge 15 by power supply 
17, the cartridge supplies a high temperature, high pressure plasma jet to 
the rear of projectile 16 which is located in barrel bore 13. The plasma 
jet is derived from a dielectric tube in cartridge 15. The tube has an 
interior wall that forms a capillary passage. When switch 21 is closed, a 
discharge voltage is applied between spaced electrodes at opposite ends of 
the tube so that an ionizable dielectric substance on the tube walls is 
ionized to form a plasma. The diameter of the tube interior across the 
passage is relatively short compared to the distance between the 
electrodes to form the capillary passage. The end of the capillary passage 
adjacent projectile 16 is flared to form a nozzle through which the jet is 
injected into barrel 13 at the rear of projectile 16. The jet expands and 
cools as it flows through the outwardly flared nozzle as it enters bore 
13. The blocked end of the capillary tube passage closes the bore in 
breech 14 in which cartridge 15 is located. The plasma in the capillary 
passage between the electrodes forms an electric discharge channel in 
which ohmic dissipation occurs to produce a high pressure. The high 
pressure in the capillary causes the plasma in the passage to flow 
longitudinally in the passage and through the open end of the passage to 
accelerate projectile 16. 
The energy of supply 17 necessary to form the plasma can be obtained from 
several different sources, such as an inductor, a capacitor bank, a 
homopolar generator, a magneto hydrodynamic power source driven by 
explosives, or a compulsator, i.e., rotating flux compressor. The electric 
energy from supply 17 heats the dielectric in the plasma source of 
cartridge 15 to a temperature in the range of 3,000.degree. K. to 
500,000.degree. K.; this is to be contrasted with the temperatures of no 
greater than 3,000.degree. Kelvin achieved with chemical explosives. 
Typical chemical explosives in cartridges contain nitrogen, oxygen, carbon 
and hydrogen. In contrast, the plasma source of cartridge 15 uses ions of 
carbon, hydrogen and electrons thereof. Due to the combination of high 
temperature and low atomic weight elements, the pressure of the plasma 
generated in the cartridge of FIG. 1 contains a large fraction of the 
plasma energy and the plasma energy is very efficiently transferred to 
kinetic energy that is applied to projectile 16. Projectile 16 is chased 
by the plasma as the plasma accelerates through barrel 13 because the 
sound speed of the plasma of these low atomic weight elements is 
relatively high compared with that for chemical charge guns. The energy 
supplied by the plasma typically exerts a pressure in the range of 100 
bars to approximately a few hundred kilobars on projectile 16. 
Reference is now made to FIG. 2 of the drawing wherein a cross-sectional 
view of cartridge 15 is illustrated as including dielectric tube 21 having 
an internal bore that forms cylindrical capillary passage 22. Dielectric 
tube 21 is formed from a dielectric ionizable substance including at least 
one element that is ionized in response to a discharge voltage from power 
supply 17. Preferably the ionizable substance is formed as an ablatable 
filler having many small, individual powder spheres 69. Spheres 69 are 
packed in tube 21 between inner and outer thin, easily ruptured 
dielectric, e.g., a copolymer of vinyl chloride and vinyl acetate, 
cylindrical walls 70 and 72 and end faces 65. The spheres 69 have a 
combined surface of 100 to 1000 times the surface area of wall 70. 
Typically the spheres 69 have an inertial mass much greater, e.g., 100 
times, than that of the plasma. The plasma quickly flows through the 
spheres and is cooled by them to help prevent ablation of the walls of 
bore 13 of barrel 12 by the plasma. Alternatively, as illustrated in FIG. 
2a, a confined water mass 81, in liquid or solid form, can be loaded in 
plastic bag 82 to provide the same result as is attained by spheres 69. 
The voltage from supply 17 is supplied across electrode assemblies 23 and 
24 having carbon segments 25 and 26 at open and closed ends of passage 22, 
respectively. Segment 26 is formed as a generally cylindrical stud having 
an outer edge that engages the interior wall of tube 21 and extends 
longitudinally into passage 22. Electrode segment 25 is formed as a carbon 
ring that abuts against planar end 55 of tube 21, to assist in holding the 
tube in situ. Ring 25 is dimensioned so that a portion of face 56 thereof 
closest to the axis of tube 21 abuts against the portion of the planar 
rear face of projectile 16 farthest from the axis of tube 21. Projectile 
16 is thereby maintained by ring 25 and collar 37 in situ in cartridge 15, 
at the breech end of barrel bore 13 and the open flared end 27 of tube 21. 
Tube 21 is flared at end 27 to form a nozzle for the plasma jet formed in 
capillary passage 22. The plasma jet flowing through outwardly flared 
nozzle 27 is injected against the back face of projectile 16 and into 
barrel bore 13, so that the jet expands and cools as it enters the barrel 
bore. 
Electrode 24, at the closed end of passage 22, includes a cylindrical metal 
segment 28 from which stub segment 26 extends. Cylindrical segment 28 is 
coaxial with stub segment 26, and has a longitudinal axis coincident with 
the longitudinal axis of tube 21 and a radius equal to the radius of wall 
72. Cylindrical segment 28 includes a threaded portion 29 which extends 
axially in the direction opposite from that of stub segment 26. Segment 29 
is threaded into a threaded bore on metal plate 31; plate 31 has a 
circular cross-section with a radius considerably greater than the common 
radii of tube 21 and cylindrical segment 28. Thus, electrode 24 is formed 
of stub segment 26, cylindrical segment 28 and metal plate 31 which block 
passage 22 at the end of dielectric tube 21 proximate the bore of breech 
14 and remote from barrel bore 13. Lead 20 is connected to plate 31 by a 
suitable connector which can fit about the circular periphery and exposed 
face of plate 31, to provide a low impedance path between power supply 17 
and electrode 24 while switch 121 is closed. 
A low impedance connection from lead 19 to carbon ring 25 of electrode 
assembly 23 is established by metal plate 32 that extends radially from 
cartridge 15 and the common axes of tube 21, and the remaining elements 
forming electrode 24, i.e., stub segment 26, cylindrical segment 28 and 
plate 31. Metal plate 32 abuts against and is fixedly connected to the 
periphery of copper sleeve 33 at the end of the sleeve remote from collar 
37. Sleeve 33 is concentric with tube 21 and the elements of electrode 24. 
Sleeve 33 is electrically insulated from tube 21 by dielectric tube 34 
that is coaxial with tube 21 and extends between plate 31 and carbon ring 
25. 
The exterior wall 70 of tube 21 and the cylindrical wall of electrode 
segment 28 abut against the interior wall of tube 34, which assists in 
holding tube 21 and electrode assembly 24 in situ. The exterior wall of 
tube 34 abuts against the interior wall of tube 33; the exterior wall of 
tube 33 abuts against the wall of the bore in breech 14 when cartridge 15 
is inserted into the breech. This construction enables sleeve 33 and tube 
34 to withstand the very high pressure which is generated in bore 22 when 
the dielectric on the interior wall of tube 21 is ionized in response to 
the application of a voltage pulse from power supply 17. 
To conduct current flowing in plate 32 and sleeve 33 to carbon ring 25, 
copper ring 36 is positioned and held in place between the inner diameter 
of sleeve 33 and the outer diameter of ring 25, so that ring 36 abuts 
against the face of tube 34 that is aligned with planar end wall 65 of 
tube 21. Ring 36 is held in situ by cylindrical collar 37 having 
longitudinally extending threaded bores into which screws 38 are threaded. 
Collar 37 is integrally formed with sleeve 39, having an interior bore 41 
that is aligned with bores 22 and 13; bore 41 has the same diameter as 
bore 13 of gun barrel 12. The diameter of bore 41 and the diameter of 
flared nozzle 27 where it intersects face 56 are approximately the same. 
Carbon ring 25, however, has a radius less than that of bore 41, so that 
the carbon ring provides a seat for projectile 16, whereby the projectile 
is positioned at the open end of the capillary passage formed by passage 
22. When cartridge 15 is loaded into breech 14 of gun 11, the periphery of 
collar 37 engages the interior cylindrical wall of the breech bore. The 
exterior co-planar faces of collar 37 and tube 39, along edge 61, engage 
forward wall 63 of the breech, between the wall of rifle bore 13 and the 
exterior of gun 11. Forward edge 62 of sleeve 33 engages corresponding 
face 64 in breech block 14. 
To electrically insulate plates 31 and 32 from each other and provide 
sufficient strength for cartridge 15 to withstand the high pressures 
generated in passage 22, plates 31 and 32 are spaced from each other by 
dielectric face plate 42, formed of a material able to withstand high 
pressure shocks, such as polyethylene. Metal plate 32 is bonded to one 
face of plate 42. The other face of plate 42 is bonded to polyethylene 
film 43. Plate 31 and film 43 are fixedly mounted on plate 42 by screws 44 
which extend through threaded bores in plates 31 and 42. 
O-rings 45 and 46 assist in holding the entire assembly in place. O-ring 45 
has inner and outer diameters approximately equal to the outer diameter of 
stub cylinder 26 and the diameter of the inner wall of tube 34, 
respectively. O-ring 45 fits between end face 65 of tube 21 remote from 
barrel 12 and shoulder 66 on cylindrical segment 28 and bears against the 
inner diameter of sleeve 34. O-ring 46 fits in peripheral, circular groove 
67 about the periphery of tube 34, and has an outer portion that bears 
against the inner diameter of annular plate 42. 
To initiate the discharge under the initial atmospheric conditions which 
exist in cartridge 15 and gun 11, electrode 24 includes an elongated 
carbon rod 71 that extends longitudinally from the tip of stub cylinder 26 
along the axis or inner wall of passage 22 into proximity with ring 25. In 
response to a pulse being supplied by supply 17 to cartridge 15, current 
flows between rod 71 and ring 25 via discharge space between the rod and 
ring. The rod is consumed by the current but the discharge between ring 25 
and cylinder 26 continues. Other types of atmospheric discharge initiators 
can be used; for example a thin carbon coating can line passage 22. 
Alternatively, for multiple shot cartridges wherein spheres 69 are 
replaced by a solid dielectric or the spheres are in containers, only one 
of which is spent with each shot, a re-usable spark plug type structure 
can be located between ring 25 and cylinder 26 and supplied with a very 
high voltage breakdown pulse immediately before switch 121 is closed. The 
breakdown caused by the spark plug type structure is occurring between 
ring 25 and cylinder 26 at the time when energy from supply 17 is 
initially applied between ring 25 and cylinder 26. 
While the discharge between electrodes 24 and 25 is occurring the energy 
from supply 17 is applied between electrodes 24 and 25 by closing switch 
121. The energy from supply 17 maintains the discharge between electrodes 
24 and 25 to cause a plasma to flow longitudinally in passage 22 to form 
an electric discharge channel between stub cylinder 26 and carbon ring 25. 
The resistance of the electric discharge channel is on the order of 
one-tenth of an ohm, which is considerably higher than any other 
resistance in the circuit between the terminals of power supply 17. 
Thereby, virtually all of the energy from power supply 17 is dissipated in 
the discharge channel formed in passage 22. The plasma formed in passage 
22 is highly ionized and very hot, with temperatures ranging from 
3,000.degree. Kelvin to as high as 500,000.degree. Kelvin. Because of the 
capillary nature of passage 22, i.e., the fact that the length to diameter 
ratio of the passage is at least ten to one, a high pressure is produced 
in the passage to cause the plasma in the capillary to flow longitudinally 
into nozzle 27. 
The breakdown between stub cylinder segment 26 and carbon ring 25 is 
initiated along inner dielectric wall 70 of dielectric tube 21 and spreads 
to dielectric spheres 69 in tube 21. Once breakdown along inner wall 70 
and of spheres 69 occurs, plasma from the inner wall and spheres rapidly 
expands radially into passage 22 to fill the capillary passage defined by 
the passage. In response to the plasma filling passage 22, there is formed 
an electric discharge channel which is effectively a resistor between 
electrodes 24 and 25. The resistance of the discharge channel can be 
expressed as: 
##EQU1## 
where R=the resistance between electrodes 24 and 25, 
l=the length of sleeve 21 between electrodes 24 and 25, 
.alpha.=exterior radius of sleeve 21, and 
.sigma.=the conductivity of the plasma in the thus formed duct. 
In response to current flowing through the plasma between electrodes 24 and 
25 ohmic dissipation in the plasma transfers energy efficiently from high 
voltage supply 17 into the plasma. Simultaneously, radiation emission and 
thermal conduction transport energy from the plasma in passage 22 to 
spheres 69, to ablate additional plasma from the spheres and replace 
plasma ejected through nozzle 27. During the period while the plasma flows 
thru passage 22, spheres 69 remain approximately in situ even though they 
are not physically confined because the plasma sweeps through the passage 
at such a high speed and with such a high pressure. Thereby, material in 
tube 21 is consumed as fuel and ejected as plasma in response to the 
electric energy provided by high voltage supply 17 when switch 121 is 
closed. 
The resulting high plasma pressure in passage 22 causes plasma in the 
passage to flow longitudinally along the passage and rapidly out of nozzle 
27. Because the other end of passage 22 is blocked by electrode 24, plasma 
can flow only out of nozzle 27. 
The length, l, radius, .alpha., and atomic species, typically hydrogen and 
carbon, in the plasma on the interior diameter of tube 21 are chosen such 
that the discharge resistance R is relatively large, such as 0.10 ohm, so 
that it considerably exceeds the sum of the resistance of power supply 17, 
leads 19 and 20, and electrodes 24 and 25. 
If cartridge 15 is to be re-usable the materials forming the cartridge must 
be able to withstand the high pressure in passage 22 accompanying a 
discharge voltage being applied between electrodes 24 and 25. If cartridge 
15 is of the single shot type, the pressure pulse formed in passage 22 and 
the materials of cartridge 15 can be such that dielectric tube 34 ripples 
and deforms in response to the pressure pulse established by the discharge 
in passage 22. The system, however, can operate satisfactorily for certain 
applications even if cartridge 15 is destroyed because barrel 12 can be 
fabricated in such a manner that it is not adversely affected by the high 
pressure generated in passage 22. In particular, if barrel 12 is 
fabricated of stainless steel with an inner tungsten liner 51, it is 
capable of withstanding a 20 kilobar pressure which can be established by 
the plasma jet. 
The material and structure of dielectric tube 21 provide the necessary low 
atomic weight elemental material, high temperature and high pressure 
necessary to achieve the desired plasma jet against the rear of projectile 
16. The high pressure is needed to accelerate projectile 16 to 
hypervelocities to provide for efficient transfer of energy from the gas 
in the plasma to projectile 16 with low losses in bore 13 of barrel 12. 
The low atomic number of the elements in spheres 69 of dielectric tube 21 
and the high temperature created by the plasma together cause the plasma 
sound speed to be very high, so that the plasma can chase projectile 16 as 
the projectile moves at high speeds in barrel bore 13. The high 
temperature of the plasma also enables a large fraction, approximately 
50%, of the plasma energy to be contained in pressure kinetic energy, 
rather than internal states of the molecules, such as ionization or 
excited atomic states. The large fraction of kinetic energy enables the 
device to be a highly efficient accelerator for converting the electrical 
energy of power supply 17 to kinetic energy of projectile 16. The specific 
cartridge structure can be scaled according to the velocity to be achieved 
for projectiles having differing masses. 
While there has been described and illustrated one specific embodiment of 
the invention, it will be clear that variations in the details of the 
embodiment specifically illustrated and described may be made without 
departing from the true spirit and scope of the invention as defined in 
the appended claims.