Gauss rifle

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The Gauss rifle , also known under the English names Coilgun or Gaussrifle (from English coil  = ' coil ', gun  = ' cannon ', rifle  = ' rifle '), is an electromagnetic accelerator for mass bullets , which - unlike the one - is also magnetic working railgun  -  coils are used to generate the magnetic fields. In principle, the coil gun principle is similar to the linear motor , which also drives the magnetic levitation train . The namesake is the German mathematician and physicist Carl Friedrich Gauß or the unit named after him for the magnetic flux density . Gauss himself only dealt with the basics of magnetism.

Animated representation of a three-stage Gauss rifle

Applications

A large number of private projects, school projects and demonstration devices deal with the variants of the principle.

In addition to the related railgun , research and development departments of armaments companies also deal with the principles of Gauss rifles. As a weapon, however, the Gauss rifle never got beyond the experimental stage.

For a similar concept only with a linear motor see: electromagnetic catapult

functionality

The Gauss rifle accelerates ballistic projectiles , the effect of which only unfolds in the target through their kinetic energy . In principle, there are two fundamentally different methods of accelerating a projectile with an arrangement of coils:

Ferromagnetic Gaussian cannon

In a ferromagnetic Gaußkanone ( English Reluctance Coil Gun ) there is a weapon comprising a ferromagnetic accelerated projectile by means of electromagnetic forces. To accelerate, electric current is passed through a coil located in front of the projectile . The magnetic field generated in the process attracts the projectile and accelerates it into the center of the coil. The magnetic field must be switched off in good time before the bullet reaches the center, otherwise it has a braking effect (imagine an arrow that remains attached to the bowstring). The sequential activation of several coils placed one behind the other enables higher and higher speeds to be achieved (so-called multi-stage coil gun ).

The short and very powerful current pulse required for this is mostly generated with the help of capacitors that are short-circuited via the coil and thus suddenly discharged. The problem is that the coil is switched off at the precise time and the saturation magnetization of the projectile. Constructions that switch off the coil current in a controlled manner when the projectile has reached a certain point have sensors and signal feedback ( closed-loop ). In systems in which the current flows through the coils until the energy store is exhausted, the location of the projectile is not detected, there is no signal feedback ( open-loop ). Such systems only work if the projectile mass is precisely matched to the electrical circuits. The ferromagnetic material from which the bullet is made also influences the magnetic fields of the coils in a non-linear manner, which makes calculations difficult.

If the electrical conductivity of the material from which the projectile is made is too high, eddy currents will be generated in the projectile due to the changing magnetic field . These not only have a braking effect on the projectile, but also heat it up through inductive heating . As soon as the temperature of the projectile exceeds the Curie temperature of its material ( 768 ° C for iron ), it ceases to be ferromagnetic. As a result, the propulsive force from the magnetic field disappears, while the braking force remains effective due to the eddy currents. This can be remedied by using ferrites with low electrical conductivity or laminated or wound dynamo sheet . Alternatively, electrically conductive material can be accelerated further after reaching the Curie point according to the principle of the inductive Gaussian gun.

Inductive Gaussian cannon

This type uses non-magnetic, electrically conductive projectiles (mostly made of copper or aluminum ). With this type, a very strong and rapidly changing magnetic field is generated in the coils. This causes a repulsive force on the projectile through eddy current or the field displacement caused by its magnetic field and accelerates it away from the coil (also known as the Thomson effect ). Here, too, the magnetic field can advantageously be generated with a capacitor that is discharged into a coil - a damped oscillation is created. The voltage of the capacitor is typically several kV so that the rate of current rise in the coil is high and strong eddy currents arise. With this method, the current pulse is usually shorter than with the ferromagnetic model. The electrical pulse does not have to be switched off at a certain point in time, which simplifies the construction. The absence of iron allows a further increase in the effect even with magnetic fields via its saturation induction - the maximum strength is essentially only limited by the mechanical strength of the coil. The projectiles usually have a ring shape, which has an advantageous effect on the induced currents and represents a compromise between the lowest possible air resistance and a large cross-sectional area.

The process is also used for material forming , see Magnetic Forming .

A special case of the inductive Gauss cannon is the plasma cannon invented by Andrei Dmitrijewitsch Sakharov in 1953 . A Type 2 Magnet Cumulative Generator (MK-2), also known as a flux compression generator , generates a magnetic field pulse of 2 million Gauss, or 200 Tesla , which induces a current of 100 million amperes. Characterized by the induced eddy currents to a 100 a small aluminum ring km / s accelerated plasma - torus evaporated. The plasma is enclosed and compressed by the magnetic field of the ring current flowing in the plasma torus ( pinch effect ). The plasma torus maintains its speed in a vacuum .

An eddy current accelerator is an arrangement in which a flat coil accelerates a conductive aluminum disc (sabot). In the middle of the disk lies a projectile (steel ball) which, due to the transmission of impulses, has a significantly higher speed (almost the speed of sound) than the disk.

advantages

Conventional weapons propelled by propellant charges are limited in their maximum muzzle velocity. The theoretically maximum achievable speed of a conventionally accelerated projectile is equal to the expansion speed of the propellant gas produced when the propellant charge burns.

A Gauss rifle, on the other hand, can theoretically reach the aerodynamic limits of the projectile that apply to all projectile weapons.

It is conceivable to align the trajectory of a bullet with a magnetic field in the muzzle area much more finely than is possible by straightening and traversing a traditional barrel. This enables fast firing sequences in which the trajectory of the previous projectile is evaluated and the next projectile is tracked in the finest range.

In fact, the exit speed that can be achieved with both methods is extremely high (several km / s) - the kinetic energy of the projectile and the resulting penetration performance are correspondingly high.

The weapons would presumably be much quieter than conventional firearms and produce less smoke that betrays the position. Since only one or a few propellant charges would be stored, the risks associated with the storage of ammunition are largely eliminated.

disadvantage

A Gauss rifle requires a lot of electrical energy to operate. So far there has been no way to store this energy in a compact and quickly accessible manner. On tanks and warships, a Gauss rifle can be connected to their power supply - but an additional, voluminous energy storage device (usually capacitors) is required, which can deliver a very high instantaneous power ( MW to GW) for a short period of time .

Due to the way Gauss rifles work, the designs are difficult to implement. In addition to the problems that occur with other magnetic weapons (weight, power supply, etc.), there are other complications:

  • High speeds can be achieved with Gauss rifles - the energy increases by the square of the speed - but the air resistance also increases by the square. This can lead to thermal destruction of the projectile, which is already heated strongly when it is launched.
  • With the currently low levels of efficiency, enormous amounts of heat are released in the weapon itself.
  • With the so-called multistage coil guns , the contribution of the front coils is decreasing due to the increasing speed of the projectile, as the action or switch-on time decreases.

literature

Individual evidence

  1. ↑ Rapp Instruments: Eddy Current Accelerator
  2. ↑ https://www.lrt.mw.tum.de/index.php?id=109 Eddy current accelerator at the Technical University of Munich