Coilgun A coilgun is a type of projectile accelerator consisting of one or more coils used as electromagnet s in the configuration of a linear motor that accelerate a ferromagnetic or conducting projectile to high velocity . In almost all coilgun configurations , the coils and the gun barrel are arranged on a common axis . The name Gauss gun is sometimes used for such devices in reference to Carl Friedrich Gauss , who formulated mathematical descriptions of the magnetic effect used by magnetic accelerators . Coilguns generally consist of one or more coils arranged along a barrel , so the path of the accelerating projectile lies along the central axis of the coils . The coils are switched on and off in a precisely timed sequence , causing the projectile to be accelerated quickly along the barrel via magnetic forces . Coilguns are distinct from railgun s , as the direction of acceleration in a railgun is at right angles to the central axis of the current loop formed by the conducting rails . Also , railguns usually require the use of sliding contacts to pass a large current through the projectile or sabot but coilguns do not necessarily require sliding contacts . Whilst some simple coilgun concepts can use ferromagnetic projectiles or even permanent magnet projectiles , most designs for high velocities actually incorporate a coupled coil as part of the projectile . The first operational coilgun was developed and patented by Norwegian physicist Kristian Birkeland . In 1934 , an American inventor developed a machine gun similar in concept to the coilgun . Except for a photo in a few publications , very little is known about it . Construction . There are two main types or setups of a coilgun : single - stage and multistage . A single - stage coilgun uses one electromagnet to propel a projectile . A multistage coilgun uses several electromagnets in succession to progressively increase the speed of the projectile . Coilguns for ferromagnetic projectiles . For ferromagnetic projectiles , a single stage coilgun can be formed by a coil of wire , an electromagnet , with a ferromagnetic projectile placed at one of its ends . This type of coilgun is formed like the solenoid used in an electromechanical relay , i . e . a current - carrying coil which will draw a ferromagnetic object through its center . A large current is pulsed through the coil of wire and a strong magnetic field forms , pulling the projectile to the center of the coil . When the projectile nears this point the electromagnet must be switched off , to prevent the projectile from becoming arrested at the center of the electromagnet . In a multistage design , further electromagnets are then used to repeat this process , progressively accelerating the projectile . In common coilgun designs , the " barrel " of the gun is made up of a track that the projectile rides on , with the driver into the magnetic coils around the track . Power is supplied to the electromagnet from some sort of fast discharge storage device , typically a battery or high - capacity high voltage capacitor s designed for fast energy discharge . A diode is used to protect polarity sensitive components ( such as semiconductors or electrolytic capacitors ) from damage due to inverse polarity of the voltage after turning off the coil . Many hobbyists use low - cost rudimentary designs to experiment with coilguns , for example using photoflash capacitor s from a disposable camera , or a capacitor from a standard cathode - ray tube television as the energy source , and a low inductance coil to propel the projectile forward . Some designs have non - ferromagnetic projectiles , of such as aluminum or copper , with the armature of the projectile acting as an electromagnet with internal current induced by pulses of the acceleration coils . A superconducting coilgun called a " quench gun " could be created by successively quenching a line of adjacent coaxial superconducting coils forming a gun barrel , generating a wave of magnetic field gradient traveling at any desired speed . A traveling superconducting coil might be made to ride this wave like a surfboard . The device would be a mass driver or linear synchronous motor with the propulsion energy stored directly in the drive coils . Another method would have non - superconducting acceleration coils and propulsion energy stored outside of them but a projectile with superconducting magnets . Though the cost of power switching and other factors can limit projectile energy , a notable benefit of some coilgun designs over simpler railguns is avoiding an intrinsic velocity limit from hypervelocity physical contact and erosion . By having the projectile pulled towards or levitated within the center of the coils as it is accelerated , no physical friction with the walls of the bore occurs . If the bore is a total vacuum ( such as a tube with a plasma window ) there is no friction at all which helps prolonged reusability . Switching . One main obstacle in coilgun design is switching the power through the coils . There are several common solutions — the simplest ( and probably least effective ) is the spark gap , which releases the stored energy through the coil when the voltage reaches a certain threshold . A better option is to use solid - state switches ; these include IGBT s or power MOSFET s ( which can be switched off mid - pulse ) and SCRs ( which release all stored energy before turning off ) . A quick - and - dirty method for switching , especially for those using a flash camera for the main components , is to use the flash tube itself as a switch . By wiring it in series with the coil , it can silently and non - destructively ( assuming that the energy in the capacitor is kept below the tube ' s safe operating limits ) allow a large amount of current to pass through to the coil . Like any flash tube , ionizing the gas in the tube with a high voltage triggers it . However , a large amount of the energy will be dissipated as heat and light , and , due to the tube being a spark gap , the tube will stop conducting once the voltage across it drops sufficiently , leaving some charge remaining on the capacitor . Resistance . The electrical resistance of the coils and the equivalent series resistance ( ESR ) of the current source are among other limits to the efficiency of a coilgun . The magnetic circuit . Ideally , 100 % of the magnetic flux generated by the coil would be delivered to and act on the projectile , but this is often far from the case due to the common air - core solenoid construction of most coilguns , which are usually relatively simple and inefficient designs made by hobbyists . With a simple air - cored solenoid , the majority of the magnetic flux is not coupled into the projectile because of the magnetic circuit ' s high reluctance . The uncoupled flux generates a magnetic field that stores energy in the surrounding air . The energy that is stored in this field does not simply disappear from the magnetic circuit once the capacitor finishes discharging , instead returning to the coilgun ' s electric circuit . Because the coilgun ' s electric circuit is inherently analogous to an LC oscillator , the unused energy returns in the reverse direction ( ' ringing ' ) , which can seriously damage polarized capacitors such as electrolytic capacitor s . Reverse charging can be prevented by a diode connected in reverse - parallel across the capacitor terminals ; as a result , the current keeps flowing until the diode and the coil ' s resistance dissipate the field energy as heat . While this is a simple and frequently utilized solution , it requires an additional expensive high - power diode and a well - designed coil with enough thermal mass and heat dissipation capability in order to prevent component failure . Some designs attempt to recover the energy stored in the magnetic field by using a pair of diodes . These diodes , instead of being forced to dissipate the remaining energy , recharge the capacitors with the right polarity for the next discharge cycle . This will also avoid the need to fully recharge the capacitors , thus significantly reducing charge times . However , the practicality of this solution is limited by the resulting high recharge current through the equivalent series resistance ( ESR ) of the capacitors ; the ESR will dissipate some of the recharge current , generating heat within the capacitors and potentially shortening their lifetime . To reduce component size , weight , durability requirements , and most importantly , cost , the magnetic circuit must be optimized to deliver more energy to the projectile for a given energy input . This has been addressed to some extent by the use of back iron and end iron , which are pieces of magnetic material that enclose the coil and create paths of lower reluctance in order to improve the amount of magnetic flux coupled into the projectile . Results can vary widely , depending on the materials used ; hobbyist designs may use , for example , materials ranging anywhere from magnetic steel ( more effective , lower reluctance ) to video tape ( little improvement in reluctance ) . Moreover , the additional pieces of magnetic material in the magnetic circuit can potentially exacerbate the possibility of flux saturation and other magnetic losses . Ferromagnetic projectile saturation . Another significant limitation of the coilgun is the occurrence of magnetic saturation in the ferromagnetic projectile . When the flux in the projectile lies in the linear portion of its material ' s B ( H ) curve , the force applied to the core is proportional to the square of coil current ( I ) — the field ( H ) is linearly dependent on I , B is linearly dependent on H and force is linearly dependent on the product BI . This relationship continues until the core is saturated ; once this happens B will only increase marginally with H ( and thus with I ) , so force gain is linear . Since losses are proportional to I , increasing current beyond this point eventually decreases efficiency although it may increase the force . This puts an absolute limit on how much a given projectile can be accelerated with a single stage at acceptable efficiency . Projectile magnetization and reaction time . Apart from saturation , the B ( H ) dependency often contains a hysteresis loop and the reaction time of the projectile material may be significant . The hysteresis means that the projectile becomes permanently magnetized and some energy will be lost as a permanent magnetic field of the projectile . The projectile reaction time , on the other hand , makes the projectile reluctant to respond to abrupt B changes ; the flux will not rise as fast as desired while current is applied and a B tail will occur after the coil field has disappeared . This delay decreases the force , which would be maximized if the H and B were in phase . Induction coilguns . Most of the work to develop coilguns as hyper - velocity launchers has used " air - cored " systems to get around the limitations associated with ferromagnetic projectiles . In these systems , the projectile is accelerated by a moving coil " armature " . If the armature is configured as one or more " shorted turns " then induced currents will result as a consequence of the time variation of the current in the static launcher coil ( or coils ) . In principle , coilguns can also be constructed in which the moving coils are fed with current via sliding contacts . However , the practical construction of such arrangements requires the provision of reliable high speed sliding contacts . Although feeding current to a multi - turn coil armature might not require currents as large as those required in a railgun , the elimination of the need for high speed sliding contacts is an obvious potential advantage of the induction coilgun relative to the railgun . Air cored systems also introduce the penalty that much higher currents may be needed than in an " iron cored " system . Ultimately though , subject to the provision of appropriately rated power supplies , air cored systems can operate with much greater magnetic field strengths than " iron cored " systems , so that , ultimately , much higher accelerations and forces should be possible . Potential uses . Small coilguns are recreationally made by hobbyists , typically up to several joules to tens of joules projectile energy ( the latter comparable muzzle energy to a typical air gun and an order of magnitude less than a firearm ) while ranging from under one percent to several percent efficiency . Much higher efficiency and energy can be obtained with designs of greater expense and sophistication . In 1978 , Bondaletov in the USSR achieved record acceleration with a single stage by sending a 2 - gram ring to 5000 m / s in 1 cm of length , but the most efficient modern designs tend to involve many stages . Above 90 % efficiency is estimated for some vastly larger superconducting concepts for space launch . An experimental 45 - stage DARPA coilgun mortar design is 22 % efficient , with 1 . 6 megajoule s KE delivered to a round . Though facing the challenge of competitiveness versus conventional guns ( and sometimes railgun alternatives ) , coilguns are being researched for weaponry . The DARPA Electromagnetic Mortar program is an example of potential benefits , if practical challenges like sufficiently low weight can be managed . The coilgun would be relatively silent with no smoke giving away its position , though a coilgun projectile would still create a sonic boom if supersonic . Adjustable yet smooth acceleration of the projectile throughout the barrel can allow somewhat higher velocity , with a predicted range increase of 30 % for a 120mm EM mortar over the conventional version of similar length . With no separate propellant charges to load , the researchers envision the firing rate to approximately double . In 2006 , a 120mm prototype was under construction for evaluation , though time before reaching field deployment , if such occurs , was estimated then as 5 to 10 + years by Sandia National Laboratories . In 2011 , development was proposed of an 81mm coilgun mortar to operate with a hybrid - electric version of the future Joint Light Tactical Vehicle . Electromagnetic aircraft catapults are planned , including on board future U . S . Gerald R . Ford class aircraft carrier s . An experimental induction coilgun version of an Electromagnetic Missile Launcher ( EMML ) has been tested for launching Tomahawk missiles . A coilgun - based active defense system for tanks is under development at HIT in China . Coilgun potential has been perceived as extending beyond military applications . Challenging and corresponding to a magnitude of capital investment that few entities could readily fund , gigantic coilguns with projectile mass and velocity on the scale of gigajoule s of kinetic energy ( as opposed to megajoule s or less ) have not been developed so far , but such have been proposed as launchers from the Moon or from Earth :