Ian R. McNab

Pulsed power for electric guns

Pulsed power requirements for electric guns are described and preferred technologies for energy storage and pulse compression are discussed. Primary approaches are rotating machines and capacitor based, pulse-forming networks, but alternative technologies that may offer some operational benefits are also discussed. These include linear magnetic flux compressors, cryogenically cooled, high-temperature superconducting inductors, novel dielectrics for energy storage, and pulsed magnetohydrodynamic (MHD) generators.

Launch to space with an electromagnetic railgun

Many advances in electromagnetic (EM) railgun and power supply technology have been made in recent years. Laboratory experiments with railguns have demonstrated muzzle velocities of 2-3 km/s and muzzle energies >8 MJ. The extension of this technology to the muzzle velocities (/spl ges/7500 m/s) and energies (/spl ges/10 GJ) needed for the direct launch of payloads into orbit is very challenging, but may not be impossible. For launch to orbit, even long launchers (>1000 m) would need to operate at accelerations >1000 gees to reach the required velocities, so that it would only be possible to launch rugged payloads, such as fuel, water, and material. A railgun system concept is described here and technology development issues are identified. Estimated launch costs could be attractively low (

Parameters for an electromagnetic naval railgun

20 000/kg), provided that acceptable launch rates can be achieved. Further evaluations are needed to establish the technical and economic feasibility with confidence.

A long-range naval railgun

The United States Navy is considering the electromagnetic (EM) railgun as a future candidate for long-range shore bombardment missions. This brief study evaluates the gun and the pulsed power supply for this application. Approximate parameters are derived for a notional system that includes the projectile, launch package, railgun, and pulsed power components.

Developments in pulsed power technology

The U.S. Navy is considering developing an electromagnetic railgun for use on future ships for long-range shore bombardment missions. The goals are to provide support for ground forces in a timely fashion, increase the ship-to-shore standoff distance, and improve ship survivability in combat situations. This paper describes the parameters of a notional railgun design that may be capable of supporting the Navys needs. The Naval Surface Fire Support mission requires a railgun capable of firing high-energy projectiles for ranges of 300-500 km with a firing rate of up to 12 rounds per minute. The notional system described here is intended to meet these requirements while providing the ability to take advantage of the integrated electric drive architecture to be used on the next generation destroyer. Several important technology issues will need to be addressed before the feasibility of such a system can be demonstrated. These issues are identified and discussed.

IAT Armature Development

The size, weight, power rating, availability and reliability of electrical power systems are important for future weapons systems. Applications could include: advanced vehicles and systems; potential new weapons; and man-portable or alternative power. Over twenty R&D studies in pulsed power have been initiated by IAT for the US Army over the last three years. Highlights of some developments in rotating machines and pulse-forming network (PFN) components are described.

Large-Scale Pulsed Power Opportunities and Challenges

This paper provides a brief overview of railgun armature development undertaken at the Institute for Advanced Technology (IAT) and elsewhere over the last decade. The fundamental physics issues that govern the armature requirements are described. These include the operating requirements, minimum parasitic mass, material action limits, contact interface pressures, electromagnetic skin effects and current nonuniformities, magnetic sawing, launch package interactions, material surface treatments, melt lubrication, gouging, and transition to arcing contact. Different bore geometries-square, rectangular, round, augmented, -turn-are also described and require matching armature and launch package designs. Novel designs are discussed, including forward tabs, magnetic obturators, splined armatures, fiber contacts, pseudoliquid armatures, plasma, and hybrid armatures.

Magnetic blow-off in armature transition

Pulsed power applications are widespread, ranging from microscopic devices up to systems that are major installations and cost many millions of dollars. This paper describes some of the approaches used for the larger systems that have been built and discusses their engineering challenges. Basic energy storage approaches include electrostatic (capacitors), magnetic (inductors), inertial (flywheels), electrochemical (batteries), and fuel or explosives. Systems based on these approaches each have their own requirements and challenges but also have many common components. An example of one potential future large-scale opportunity-launch to space-is given and the need to develop more competitive economic approaches is discussed.

Experiments with the Green Farm electric gun facility

Magnetic blow-off forces play an important role in arcing and failure of electrical joints and contacts in electrical systems under high current fault conditions. Magnetic blow-off forces arise from concentration of current in the contact interface and tend to blow the contacts apart, causing separation and arcing. Simple models have been developed to predict the magnitude of these forces and permit the design of joints and contacts that can successfully resist the forces. In this paper, the role of magnetic blow-off in railgun armature contacts is explored. It is shown that magnetic blow-off forces are important and may be the final step in a series of events that ultimately leads to transition. Models that predict the conditions under which blow-off will occur are developed, and supporting experimental data is described.

Present and Future Naval Applications for Pulsed Power

The design and construction of a major electric gun facility at Green Farm in San Diego is described. The facility is driven by an 11 kV 32 MJ capacitor bank, arranged in 4 MJ modules that can be independently triggered to provide a choice of pulse shapes. The bank has powered a variety of EM and ET guns, including an 8-meter Single Shot Rail gun and a modified 5-inch Naval gun. World record high energy and high velocity shots have been achieved. The highest rail gun muzzle energy was 8.6 MJ and the highest muzzle velocity was 4.3 km/s with a plasma driven projectile of 0.64 kg, corresponding to a muzzle energy of 6 MJ. Intact projectile launch and flight was confirmed by high speed (8000 frames/sec.) photography and flash X-rays. >