TECHNOLOGY AREAS: Materials/Processes, Electronics, Weapons

ACQUISITION PROGRAM: Office of Naval Research Code 352: Electromagnetic Railgun (EMRG) INP

OBJECTIVE: Develop a flexible, compact cable or conductor capable of handling the repetitive, high magnitude, high transient, pulsed loading and flexing service required by a Naval Electromagnetic Railgun (EMRG).

DESCRIPTION: The US Navy is pursuing the development of an electromagnetic railgun for long range naval surface fire support. An electromagnetic railgun consists of two parallel electrical conductors, called rails, and a moving element, called the armature. Very high current (~5-6 mega-amps) is passed down one rail, through the armature, and back through the other rail. The armature is accelerated down the barrel due to the interaction between this magnetic field and current flow (Lorentz Force). An electromagnetic rail gun (EMRG) system will accelerate projectiles to hypersonic speeds, enabling ranges beyond 200 NM in less than 6 minutes of flight time while traversing the atmospheric spectrum (endo-exo-endo). The EMRG can address time-critical targets with a rate-of-fire of 6 to 12 rounds per minute while residual energy at target impact provides lethal effects.

A flexible power connection at the railgun breech is required to accommodate launcher recoil and train and elevate motions. This connection must deliver ~5- 6 mega-amps (MA) for 8-10 ms to the launcher at a repetition rate of 6 to 12 pulses per minute. The cable/conductor should be compact due to the limited volume near the launcher and due the limited surface area for electrical connections at the launcher. Because a compact conductor will have less cross-sectional area, significant heating is expected and a means to reduce or mitigate this heating will be required. The required high voltage insulation further impedes the removal of heat. The cable/conductor must also contain the magnetic fields generated within the cable/conductor and withstand the associated electro-magnetic forces between conductors.

Because high current is present throughout the EMRG pulsed power system, this conductor may have use in other parts of the system.

PHASE I: Develop a flexible power conductor design that meets the Naval EMRG requirements and substantiate the design through analysis, simulations and scaled testing as appropriate. Demonstrate how the proposed technology could scale up to current and power levels required for a full scale EMRG.

PHASE II: Fabricate representative section of full-scale design and demonstrate operation. Deliver representative conductors to the Navy for integration and testing in prototype EMRG pulsed power systems.

PHASE III: Design and deliver a complete conductor system for integration into and EMRG prototype, and ultimately, into a high repetition rate shipboard or land-based test site EMRG system.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: This type of conductor is applicable to any commercial process that requires continuous-duty high-power transfer that is coupled with mechanical movement or commercial systems that suffer from excessive conductor heating but require compact conductors.

REFERENCES:
1. Fridman, B. E.; "Skin-Effect in Massive Conductors and Transients in Electrical Circuits of Pulsed Power Facilities", Magnetics Conference, 2006. INTERMAG 2006. IEEE International, 8-12 May 2006 Page(s):65 � 65.

2. Dableh, J.H.; Findlay, R.D.; Colquhoun, I.L.; Truemner, M.E.; "Cable for High Pulse Power Applications", IEEE Transactions on Power Apparatus and Systems; Volume PAS-104, Issue 8, Aug. 1985 Page(s):1963 � 1967.

3. Jamison, K.A.; Stearns, R.E.; Klug, R.B.; Ford, R.D.; "High energy cable development for pulsed power applications", Magnetics, IEEE Transactions on, Volume 27, Issue 1, Jan 1991 Page(s):374 � 379.

4. Kerrisk, J.; "Railgun conductor heating from multiple current pulses", Magnetics, IEEE Transactions on, Volume 22, Issue 6, Nov 1986 Page(s):1561 � 1566.

5. Lombardi, A.; Donazzi, F.; Taralli, C.; Tencer, C.; Lima, A.J.O.; "Heat transfer in forced cooled cables", Power Delivery, IEEE Transactions on; Volume 5, Issue 1, Jan. 1990 Page(s):8 � 13.

6. Carpenter, C.J.; "Action-reaction forces between current-carrying conductors", Science, Measurement and Technology, IEE Proceedings - Volume 153, Issue 2, 9 March 2006 Page(s):73 � 80.

KEYWORDS: Electromagnetic launcher; railgun; cable; high power; flexible; conductor; pulsed power

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