United States Patent (19) 11 4,343,223 Hawke Et Al
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United States Patent (19) 11 4,343,223 Hawke et al. 45) Aug. 10, 1982 54 MULTIPLESTAGE RAILGUN UCRL-52778, (7/6/79). Hawke. 75 Inventors: Ronald S. Hawke, Livermore; UCRL-82296, (10/2/79) Hawke et al. Jonathan K. Scudder, Pleasanton; Accel. Macropart, & Hypervel. EM Accelerator, Bar Kristian Aaland, Livermore, all of ber (3/72) Australian National Univ., Canberra ACT Calif. pp. 71,90–93. LA-8000-G (8/79) pp. 128, 135-137, 140, 144, 145 73) Assignee: The United States of America as (Marshall pp. 156-161 (Muller et al). represented by the United States Department of Energy, Washington, Primary Examiner-Sal Cangialosi D.C. Attorney, Agent, or Firm-L. E. Carnahan; Roger S. Gaither; Richard G. Besha . - (21) Appl. No.: 153,365 57 ABSTRACT 22 Filed: May 23, 1980 A multiple stage magnetic railgun accelerator (10) for 51) Int. Cl........................... F41F1/00; F41F 1/02; accelerating a projectile (15) by movement of a plasma F41F 7/00 arc (13) along the rails (11,12). The railgun (10) is di 52 U.S. Cl. ....................................... ... 89/8; 376/100; vided into a plurality of successive rail stages (10a-n) - 124/3 which are sequentially energized by separate energy 58) Field of Search .................... 89/8; 124/3; 310/12; sources (14a-n) as the projectile (15) moves through the 73/12; 376/100 bore (17) of the railgun (10). Propagation of energy from an energized rail stage back towards the breech 56) References Cited end (29) of the railgun (10) can be prevented by connec U.S. PATENT DOCUMENTS tion of the energy sources (14a-n) to the rails (11,12) 2,783,684 3/1957 Yoler ...r. 89/8 through isolation diodes (34a-n). Propagation of energy 2,790,354 4/1957 Yoler et al. ............................... 89/8 from an energized rail stage back towards the breech 3,279,320 10/1966 Rosebrock ................................ 89/8 end of the railgun can also be prevented by dividing the 3,417,273, 12/1968 Gates et al. ............................... 89/8 rails (11,12) into electrically isolated rail sections 3,613,499 10/1971 Hubbard et al. (11a-n, 12a-n). In such case means (55a-n) are used to 4,010,396 3/1977 Ress et al. ....... extinguish the arc at the end of each energized stage and a fuse (31) or laser device (61) is used to initiate a new OTHER PUBLICATIONS plasma arc in the next energized rail stage. UCRL-82677, (5/25/79). Hawke et al. UCRL-82762, (7/10/79) Hawke. 9 Claims, 13 Drawing Figures U.S. Patent Aug. 10, 1982 Sheet 1 of 4 4,343,223 (AR/OA. AA7 ) 2 23 22 A/G 5 (PRIOR ART) U.S. Patent Aug. 10, 1982 Sheet 2 of 4 4,343,223 DZI 2 D/2 2/4 U.S. Patent Aug. 10, 1982 Sheet 3 of 4 4,343,223 O 6 p/ IOa - Q 62 63 15 /Ob I- SNSSKNX%U CSA - Ib 12a ". ZZZZZZZ ZZZZZYZZZZZZZZZZZZZZZ - -- 52 (f) (f) XSE H. CD CO 2 -5 L us s t E 1. O O2 O.4 O6 O.8 O RAIL FRACTION CfO of I.O 9 O8 - O6 2 O4 Z u O2 2 5 O. 2 4 6 8 O 2O 4O6O IOO EQUAL-LENGTH ACCELERATOR STAGES A/G /O U.S. Patent Aug. 10, 1982 Sheet 4 of 4 4,343,223 OO A/G // REQUIRED ENERGY FOR -, IO-, AND OO-SAGE RAILGUNS 5 O A/G /2 IOO-STAGE ACCELERATOR WITH EQUAL-LENGTH STAGES PROJECTLE VELOCITY-km/S 6 O O 4. O O 2 O O O 2O 4O 6O 8O OO STAGE - in 2OO IOOO ENERGY REQUIRED 8OO 6OO-- ENERGY A/G /3 OO-STAGE ACCELERATOR WITH EQUAL TRANST 4OO -- TME STAGES 4,343,223 1. 2 and 30. Rails 11 and 12 are electrically connected to MULTIPLESTAGE RAILGUN busbars 28 and 30, respectively. As the shuttle switch 26 moves across the breech end of the rail gun, out of The invention described herein arose at the Law contact with busbar 28 and into contact with busbar 29, rence Livermore Laboratory under, or in the course of, fusible wire 31, connected between the rails 11 and 12 Contract No. W-7.404-ENG-48 between the United will initially conduct current but will quickly vaporize States Department of Energy and the University of and establish the plasma arc. (If the PESD is a capacitor California. bank, busbars 27 and 30 are shorted together and shuttle switch 26 is not needed). TECHNICAL FIELD O The plasma arc 13 and projectile 15 will then acceler This invention relates to magnetic railgun accelera ate along the rails 11 and 12. Prior to the arc exiting the tors. discharge end 32 of the railgun, crowbar switch 33 is closed to extinguish the plasma arc and avoid spurious BACKGROUND ART arcing. The promise of abundant energy has inspired many 15 The use of a plasma arc as an armature 13 for acceler approaches to controlled thermonuclear fusion. Pellets, ating the projectile has several advantages over a slid ignited one per second, could be the energy source for ing metallic conductor. First, the plasma arc easily power plants producing billions of watts of electrical maintains contact with the rails. Secondly, a conducting power. To achieve ignition, one would have to deliver metallic armature resistively melts. Thirdly, a sliding about 1 megajoule (MJ) of energy to a deuterium 20 metal contact experiences a large erosive drag force. tritium (DT) pellet in about 10 nanoseconds (ns). Candi date igniters have included laser, electron, and heavy Acceleration, a, of the projectile 15 is given by and light-ion beams. Another approach would be to ignite a DT pellet X B LP with the impact of a projectile weighing about 0.1 gram. 25 2n Such a projectile could be accelerated to hyperveloicty (150 km/s or more) by a magnetic, accelerator. The where I is the current in the arc, w is the rail spacing, B advantage of the use of a projectile is that the energy is the magnetic-field intensity in the region of the arc, m would be concentrated into a small volume. If the pro is the mass of the projectile, and L1 is the inductance per jectile moves rapidly enough to contain the energy, 30 unit length of the rail gun. then it would be easy to deliver the energy in the re quired 10 ns by making the projectile short enough. The projectile velocity, v, is given by The present invention relates to an electromagnetic railgun as a projectile launch device. In order to better understand the present invention, 35 whereint is time, and the projectile position z, is given the operating principles and limitations of a prior art by electromagnetic railgun system, as exemplified in FIGS. 1-3, should first be considered. z= widt. A railgun accelerator 10, as shown in FIG. 1, is a linear dc motor consisting of a pair of rigid, electrically At high current density, the plasma-arc voltage, VA, and field-conducting rails 11 and 12 and a movable is nearly independent of the arc current and is equal to conducting armature 13. Basically, the armature 13 is about 200 v. accelerated along the rails as a result of the Lorentz The voltage, VI, resulting from the time variation of force produced by the current, I, from a primary ener the current and inductance, L, of the railgun, is given by gy-storage device (PESD) 14, in the armature 13 inter 45 acting with the magnetic field B produced by the cur rent in the rails 11 and 12. The armature 13 acts upon the rear of projectile 15 to accelerate it down the rails 11 and 12. Preferably, a plasma arc is used as the armature 13, 50 Since L = L1z, then (dL/dt)=Liv. the arc being produced between the rails by the PESD The voltage, VR, along the two rails is given by 14. Typically, a rail gun assembly may be as shown in FIG. 2, with a dielectric 16 serving to maintain the rail position, to form with rails 11 and 12 the bore 17 of the railgun, and to confine the plasma arc armature 13 be 55 where R is the resistance of each rail. hind the projectile 15. A jacket 18, of steel for example, Using Kirchhoff's law, serves as the supporting barrel of the railgun. A typical rail gun system, as shown in FIG. 3, func tions as follows. A PESD 14, such as a capacitor bank IR + L-E- + IR + I-I- + L-E- + V = O, or homopolar generator, is used to generate a current in the storage inductor 21 after switch 22 is closed. When from which the current and voltages are calculated. the desired, usually maximum, current is established in (Stray circuit resistance and inductance are included in inductor 21, switch 24 is closed to isolate the PESD 14 Ro and Lo of resistance 23 and inductance 21, respec from the circuit. At this time, and if the PESD 14 is a tively. homopolar generator, shuttle switch 26, such as a slid 65 The following equation may be used to calculate the ing multifingered conductor initially bridging between distribution of energy throughout the projectile's accel the two busbars 27 and 28, is moved across the breech eration. The instananeous energy, Ec, in the storage coil end 29 of the railgun 10 to bridge between busbars 28 21 is 4,343,223 4. where the total voltage appears.