adividedworld.com 4/17/2017
U.S. naval and military planners are salivating at the possibilities of railguns. Railguns are electromagnetic artillery weapons whose projectiles have muzzle velocities not limited by the speed of propellant gasses, but are limited only by the amount of electrical current used to propel them. Traveling at hypersonic speeds in excess of mach 5, the projectiles do not require an explosive filler to effect their damage. It is simply their very high kinetic energy that gives them their killing power. Also because of their very high speeds, railguns are suitable for terminal point antimissile defense, conceivably even against Intercontinental Ballistic Missiles (ICBMs).
What a Railgun Is
I wrote briefly about railguns in conjunction with how we might defend against hypersonic glide vehicles (HGVs) being developed by Russia and China, in the post Defenses Against Hypersonic Glide Vehicles. Instead of expanding gasses inside an artillery tube propelling the projectile, a magnetic force acting on a current, often called a Lorentz force, propels the projectile. The basic idea behind the railgun is illustrated below.
Consider the figure on the far right. Two long, parallel conducting rails are in electrical contact with a sliding armature that is perpendicular to both rails. When a voltage difference is applied between the two rails at the ends labeled “+” and “-“, a current directly proportional to the voltage difference flows down one rail, shunted across the sliding armature, and then back the reverse direction along the second rail to the other pole of the potential difference. If you were to take the thumb of your right hand and point it in the direction of the current, curling your fingers around the rail, the curled fingers would point in direction of the magnetic field lines produced by the current, which are approximately circular around the conducting rail. This is called the “right hand rule,” and the magnetic field lines produced are illustrated as the blue circles surrounding the rails. Note that in the figure, this produces magnetic fields that all point upwards in-between the rails, and downwards outside the rails in the plane defined by the rails and the armature. The magnetic fields from all parts of the current loop add to each other constructively inside the current loop. Maxwell’s electromagnetic field equations tell us the amplitude of the produced magnetic field is directly proportional to the amplitude of the current.
In addition, a magnetic field produces a force on the current, the direction of which can be determined by yet another right hand rule: If you point the fingers of your right hand in the direction of the current and then curl them in the direction of the magnetic field, the thumb will point in the direction of the force, as illustrated in the figure. The rails and the power supply are clamped down so that they are not allowed to move. The armature however is allowed to slide precisely in the direction the force on it is pointing, causing it to accelerate in the parallel direction of the rails. If we attach some kind of projectile to the armature, or even better make the armature part of the projectile, such that the projectile is released when the armature reaches the end of the rails, the projectile is accelerated together with the armature to be released into free-space at the end of the rail gun. Because the magnetic field is directly proportional to the current magnitude, and the Lorentz force is directly proportional to both the magnetic field and current being accelerated, the acceleration of the projectile down the rail gun is directly proportional to the square of the current: double the current and you get four times the acceleration.
More:
http://www.adividedworld.com/security-issuses/u-s-railgun-systems-proliferate/
