Rail Guns

Ashutosh Kumar Rai

Roll-86

B. Tech. Part-IV

What is a Rail Gun?• Simply put, a rail gun is a gun that launches shells

(projectiles) using magnetic fields and current instead of consumed fuel.• Railgun theory is based on the Lorenz force

phenomenon.

History• In 1944, using batteries as his

power source, Joachim Hänsler created the first working railgun, which was able to propel a 10 g mass to speeds of about 1mile/s.

• 1964-MB Associates used a 28kJ Capacitor to accelerate 5 and 31 mg nylon cubes with a plasma arc as the armature with speeds of 5-6 mile/s.

Components

Two Rails Power Supply Armature Firing Circuitry Shell Breach

THE RAILS

• Material:

The best rail material will depend on specific design. Important characteristics of a good rail material are high conductivity, high strength, high machinability, resistance to corrosion, high melting point, availability, compatibility with slug material, and finally price.

• Shape• The contact patch between rail and shell. • Dependent on shape and type of shell.• The structural rigidity of the rail in the horizontal plane

(in plane with but perpendicular to projectile motion). • The shape and size of shell determine the speeds that

can be achieved by it.

ARMATURE

• The armature, which drives the shell, closes the electromagnetic loop between the rails and is forced along their length at extremely high speed.

Different types– Solid piece of conductive metal

(Conductive sabot housing a dart or sub-calibre penetrator)

– Metallic plasma for very high velocity shots

ARMATURE (cont.)The Sabot (proposed design)

• Benefits

• optimum current carrying capacity and heat dissipation.

• projectile itself may be designed for more stability and less drag.

• Speeds up to 10mile/s.

The Power Supply and Firing Circuit Components• Rail guns require tremendous currents to fire a projectile

at great speed. Typically, the current used in medium-large calibre rail guns is in the millions of amperes, while the duration will be less than 10ms. Maintaining a high current as long as possible increases the amount of energy input to the projectile.

• AC Source • Transformers• Capacitors• Inductors• Switches

Working• It can be shown from the Biot-Savart law that the magnetic

field at a given distance s from an infinite current-carrying wire is given by:

• So, in the space between two infinite wires separated by a distance, d, the magnitude of the field is:

• To obtain an approximate expression for the average magnetic field on a rail gun armature, we assume that the rail radius r is small compared with the rail separation d and, by assuming that the rail gun rails can be modelled as a pair of semi-infinite conductors, we compute the following integral:

• By the Lorentz force law, the magnetic force on a current-carrying wire is given by IdB, so since the width of the conductive projectile is d, we have (assuming l>3d):

• a(acceleration)=IdB/M(mass of shell)

• So, Acceleration directly proportional to charge flow (I).

Problems• Repulsion• Each rail in a rail gun carries a current anti-parallel to the

current in the other rail. The laws of physics show that two anti-parallel currents repel each other. Since the currents in a rail gun are large the repulsion between the two rails is very large. Rail guns thus have the tendency to break after a few uses, which makes them not very cost effective.

• F = q . (v X B)

• High TemperaturesBecause the rails in a rail gun are not super conductors they

have a resistance. Since the current that must go into a rail gun is so massive the amount of heat that is produced this way is very high and thus may fuse the projectile to the rails which will either render the rail gun useless or slow down the acceleration of the projectile. A solution to this problem is to make the rails in a rail gun super conductors.

Benefits• Extremely Fast• hold the record for fastest object

accelerated of a significant mass, for the 16000m/s firing of a .1 gram object

• Can propel large masses• 32Megajoule gun fires a

1.6kilogram projectile at 3300m/s • Extremely Accurate

Applications• Military Applications• Tanks• Battleships• Star Wars• Destroying Asteroids and

meteorites• Destroying planes (Anti

aircraft warfare).

Peaceful applications• Peaceful Applications• Electric Trains: Using magnetic levitation and linear

motors for building fast locos.• Space launch: In place of shell rockets, satellites can be

launched from appropriate carriers.• Nuclear Fusion is triggered by very high temperature and

pressure at the core: -- Lasers, usually over 100, to concurrently strike a

fuel pellet, creating a symmetrical compressive pressure. -- Rail guns may be able to trigger fusion by firing

energetic plasma from multiple directions.

Latest ExperimentsSeven-pound bullet emerged from a truck-sized contraption at seven times the speed of sound and sent a visible shockwave through the air before crashing into a metal bunker filled with sand. With 10.6 mega joules of kinetic energy, this aluminium slug was propelled not by explosives but by an electric field,

making this the most powerful

electromagnetic rail gun ever fired.

The device is part of the US navy’s

rail gun development program.

Showing launch of rail gun at US naval warfare center

• US Navy.

Showing the shell

Comparison

• Normal Guns (Naval guns)

• Range of 20 miles• Speed: Subsonic. Less than

Mach 1.• Explosives have limit upto

which they can provide speed to the shell.

• Rail Gun• Range of 200 miles and above.• Speed: Mach 7-8 (Hypersonic)• No such speed limit.

The capabilities of Rail gun are even greater than that of cruise missiles like TomaHawk and BrahMos.

References• http://members.tm.net/lapointe/EMGuns.html• http://home.insightbb.com/~jmengel4/rail/rail-rails.html• http://www.powerlabs.org/railgun.htm• Junya Kitamura,” Formation And Analysis of Dense Boron Carbide

Coatings with A Low Porosity Formed by Electomagnetically Accelerated Plasma Sprying,” August 6,2001,pp.632-635.

• http://www.rit.edu/~dih0658/apps.html• http://www.dstl.gov.uk/pr/science_spot/off_the_rails3.htm• http://members.tm.net/lapointe/EMGuns.html