Railgun

src: nationalinterest.org

railgun is a device that uses electromagnetic force to launch high speed projectiles, using accelerated sliding armatures along a pair of conductive rails. These are usually built as weapons and projectiles usually do not contain explosives, depending on the projectile high speed to inflict damage. The railgun uses a pair of parallel conductors, or rails, in which a sliding armature is accelerated by the electromagnetic effect of the current flowing down one rail, into the armature and then back along the other rails. It is based on a principle similar to that of a homopolar motor.

In 2014 railgun is being researched as a weapon that uses electromagnetic forces to provide very high kinetic energy to projectiles (eg APFSDS) rather than using conventional propellants. While explosive-powered military weapons can not easily reach a muzzle velocity of more than 2 km/sec, the railgun can easily exceed 3 km/sec. For the same projectile, the range of railgun can exceed conventional weapons. The destructive strength of the projectile depends on its kinetic energy at the point of impact and because of the large relief speeds the projectile launches, its destructive force may be much larger than the conventionally launched projectile of the same size. The absence of explosives or explosive warheads for storing and dealing, as well as low-cost projectiles compared to conventional weaponry, comes as an added advantage.

Apart from the above advantages, the railgun is still very much at the research stage in 2014, and it remains to be seen whether railgun will ever be deployed as a practical military weapon. Any trade-off analysis between the electromagnetic propulsion (EM) system and chemical propellant for weapon applications should also take into consideration the novelty and complexity of the pulsed electrical supply required for the electromagnetic launcher system.

In addition to military applications, NASA has proposed to use railgun to launch "wedge-shaped planes with scramjets" to an altitude at Mach 10, where they will then fire a small charge into orbit using conventional rocket propulsion. The extreme g-force involved with direct ground-rail launch into space can limit usage only to the strongest load. Alternatively, very long rail systems can be used to reduce the required launch acceleration.

Video Railgun

Basics

In its simplest (and most commonly used) form, a different railgun of an unused traditional electric motor is made of additional field windings (or permanent magnets). This basic configuration is formed by a current loop and thus requires a high current (for example, from a one million ampere order) to produce sufficient acceleration (and muzzle velocity). The relatively common variant of this configuration is the expanded railgun in which the driving current is routed through an additional pair of parallel conductors, arranged to increase ("add") the magnetic field experienced by the mobile armature. This setting reduces the flow required for the given acceleration. In terms of electric motors, the added railgun is usually a series-wound configuration. Some railguns also use a strong Neodymium magnet with a field perpendicular to the current flow to improve the force on the projectile.

Armature can be an integral part of projectiles, but can also be configured to speed up separate, isolated or non-conducting projectiles. Solid, metallic shear conductor is often the preferred form of armature railgun but "plasma" or "hybrid" armatures can also be used. A plasma armature is formed by an ionized gas arc used to drive a solid, non-conductive charge in a manner similar to the propellant gas pressure in a conventional weapon. A hybrid armature uses a pair of "plasma" contacts to connect the metal armature to the rifle rail. Solid fleets can also "transition" into hybrid armatures, usually after certain speed thresholds have been exceeded.

Railgun requires a pulsating DC power supply. For potential military applications, railguns are usually attractive because they can reach much larger muzzle velocities than guns driven by conventional chemical propellants. Increased muzzle velocity with better aerodynamic projectiles can convey the benefits of increased temporary range of shooting, in terms of target effects, terminal speed increases can allow the use of kinetic energy spins that incorporate a hit-to-kill guide, in lieu of for explosive shells. Therefore, a typical military railgun design aims for a muzzle velocity in the range 2000-3500 m/s with a 5-50 Megajoules (MJ) snout energy. In comparison, 50MJ is equivalent to the kinetic energy of a school bus weighing 5 metric tons, with a speed of 509 km/h (316 mph). For a single-loop railgun, this mission requirement requires a rollout of several million amperes, so a typical railgun power supply may be designed to deliver 5 MA launch currents for several milliseconds. Since the magnetic field strength required for such launches is usually about 10 tesla (100 kilogauss), most contemporary railgun designs are effectively "air-core", that is, they do not use ferromagnetic materials such as iron to increase magnetic flux. However, if the barrel is made of a magnet permeable material, the strength of the magnetic field increases as the permeability increases (? = ₀ * ? _r , where is an effective permeability, ₀ is a constant permeability and ? _r is the relative permeability of the barrel). This automatically increases the power.

The railgun speed is generally within the range that two-stage gas firearms can attain; However, the latter is generally only considered suitable for laboratory use, while railgun is rated to offer some potential prospects for development as a military weapon. Another light gas gun, Combustion Light Gas Gun in the form of 155 mm prototype is projected to reach 2500 m/s with a caliber of.70 caliber. In some hypervelocity research projects, the projectile is "pre-injected" into the railgun, to avoid the need to stand up, and both two-stage gas firearms and conventional gun powder have been used for this role. In principle, if railgun power supply technology can be developed to provide a unit that is safe, compact, reliable, opponent, and lightweight, the total volume of system and mass required to accommodate such a supply and the main fuel can be less than required. total volume and mass for the equivalent number of missions of conventional propellant and explosive ammunition. It is possible that such technology has matured with the introduction of the Electromagnetic Aircraft Launch System (EMALS) (although railgun requires much higher system power, since nearly the same energy must be transmitted in milliseconds, compared to a few seconds). Such developments would then provide further military benefits because the removal of explosives from military weapon platforms would reduce its vulnerability to enemy fire.

Maps Railgun

History

The earliest electromagnetic gun developed was a coil gun. Its development was reportedly commenced in 1845. The first patent was awarded to Prof. Kristian Birkeland of the University of Kristiania (today Oslo). He speeds up a 500 g projectile to 50 m/s.

In 1918, the French inventor Louis Octave Fauchon-Villeplee invented the electric cannon. He filed a US patent on April 1, 1919, issued in July 1922 as patent no. 1,421,435 "Electrical Appliances to Encourage the Project". In the device, two parallel busbars are connected by projectile wings, and the entire equipment is surrounded by a magnetic field. By passing the current through the busbar and projectile, an induced force drives the projectile along the bus-bar and flies.

In 1944, during World War II, Joachim HÃÆ'¤nsler of the German's Ordnance Office filed the theoretical first railgun. By the end of 1944, the theory behind his anti-aircraft gun had been enough to enable the Luftwaffe's Flak Command to issue a specification, which demanded a muzzle speed of 2,000 m/s (6,600 ft/s) and the projectile contained 0.5 kg (1.1 pounds) of explosives. The weapons had to be installed in a six-shot twelve-inch revolutions per minute, and that was to match the 12.8 cm FlaK 40 mount. It was never built. When details were discovered after the war, it aroused interest and a more detailed study was conducted, culminating with a 1947 report that concluded that it was theoretically viable, but each weapon would require enough strength to illuminate half of Chicago.

During the year 1950, Sir Mark Oliphant, an Australian physicist and first director of the School of Physical Sciences Research at the new Australian National University, embarked on the design and construction of the largest homopolar generator (500 megajoules) in the world. It operated from 1962 and was later used to power a large scale railgun that was used as a scientific experiment.

Since 1993, the British and American governments have collaborated on a railgun project at the Dundrennan Arms Testing Center which culminated in a 2010 test in which BAE Systems fired a 3.2 kg (7 lb) projectile at 33 megajoules.

In 1994, the Development of DRDO Research and Development Armaments of India developed a railgun with 240 kJ, a low inductance capacitor bank operating at 5 kV power can launch 3-3.5 g heavy projectiles up to speeds over 2.00 km/sec.

In 2010, the United States Navy tested the BAE Systems compact railgun designed for ship emplacement that accelerates 0.2 kg (7-pound) to hypersonic projectiles of approximately 2.4 kilometers per second (8,600 km/h), or around Mach 7, with 33 megajoules of kinetic energy. This is the first time in history that such performance levels are achieved. They gave the motto project "Velocitas Eradico", Latin for "I, [who] fast, eradicate" - or in ordinary language, "Speed ​​of Killing". The previous railgun with the same design (32-megajoules) was at the Dundrennan Arms Testing Center in England.

Low power, small-scale railgun has also made popular lecture and amateur projects. Some amateurs actively conduct research on railgun; examples can be found on YouTube.

src: i.ytimg.com

Design

Theory

The railgun consists of two parallel metal rails (hence the name). At one end, these rails are connected to an electrical power supply, to form a puncture tip. Then, if a conductive projectile is inserted between the rails (eg by inserting into the breech), it completes the circuit. The electrons flow from the negative terminal of the power supply go up the negative rail, cross the projectile, and down the positive rail, back to the power supply.

This current makes the railgun behave as an electromagnet, creating a magnetic field inside the loop formed by the length of the rail to the armature position. In accordance with the rule of the right hand, the magnetic field circulates around each conductor. Since the current is in the opposite direction along each rail, the net magnetic field between the rails ( B ) is directed at right angles to the plane formed by the central axis of the rail and armature. In combination with the current ( I ) in the armature, this produces a Lorentz force that accelerates the projectile along the rails, always out of the loop (apart from the polarity supply) and away from the power supply, toward the end of the ridge muzzle. There are also Lorentz troops working on the tracks and trying to separate them, but because the rails are fitted firmly, they can not move.

By definition, if a current current flows in a pair of infinite parallel conductors separated by a distance of one meter, then the magnitude of force in each conductor meter will be exactly 0.2 micro-Newton. Furthermore, in general, the force will be proportional to the square of the current magnitude and inversely proportional to the distance between the conductors. It also follows that, for a railgun with a projectile mass of several kg and a barrel length of several m, a very large current would be required to accelerate the projectile at a speed of 1000 m/s.

The enormous power supply, providing on the order of a million current amperes, will create tremendous power on the projectiles, accelerating to speeds of many kilometers per second (km/s). Although this speed is possible, the heat generated from object propulsion is sufficient to rapidly erode rails. Under high usage conditions, current railgun will require frequent rail replacement, or use heat resistant materials sufficiently conductive to produce the same effect. At this time, it is generally recognized that this will require a major breakthrough in materials science and related discipline to produce a high-powered railgun capable of firing more than a few shots from a set of rails. The barrel must withstand this condition for several revolutions per minute for thousands of shots without significant failure or degradation. This parameter is far beyond the state of the art in materials science.

Mathematical formula

This section presents some basic analyzes of fundamental theoretical electromagnetic principles governing railgun mechanics.

Jika railgun adalah untuk menyediakan medan magnet yang seragam dari kekuatan ${\ displaystyle B}  ÂÂ$ , berorientasi pada sudut kanan ke kedua angker dan sumbu bore, kemudian, dengan arus jangkar ${\ displaystyle I}  ÂÂ$ dan panjang armature ${\ displaystyle {\ boldsymbol {\ ell}}}  ÂÂ$ , gaya ${\ displaystyle F}  ÂÂ$ mempercepat proyektil akan diberikan oleh rumus:

${\ displaystyle {\ boldsymbol {F}} = I {\ boldsymbol {\ ell}} \ kali {\ boldsymbol {B}}}  ÂÂ$

Here the force, the current and the field are all treated as vectors, so that the cross-product of the above vectors gives a force directed along the bore axis, which works on the current in the armature, as a consequence of the magnetic field.

In most simple railgun, the magnetic field ${\ displaystyle B}$ is only provided by the current that flows on the rails, which is behind the armature. Therefore the magnetic field will not become constant or uniform spatially. Therefore, in practice, force must be calculated after making allowances due to the spatial variation of the magnetic field above the armature volume.

To illustrate the principles involved, it can be useful to consider rails and armature as thin cable or "filament". With this approach, the force vector size can be determined from Biot-Savart's legal form and the result of Lorentz's style. Styles may be mathematically derived in terms of permeability constant ( ${\ displaystyle \ mu _ {0}}$ $$ ), the radius of the rails (which are assumed to circulate in a cross section) ( ${\ displaystyle r}$ ${\ displaystyle d}$ ) and the stream ( ${\ displaystyle I}$) as described below.

Pertama, dapat ditunjukkan dari hukum Biot-Savart yang pada salah satu ujung kabel pembawa arus semi tak hingga, medan magnet pada jarak tegak lurus yang diberikan ( ${\ displaystyle s}  ÂÂ$ ) dari ujung kabel diberikan oleh

${\ displaystyle \ mathbf {B} (s) = {\ frac {\ mu_ {0} I} {4 \ pi s}} {\ widehat {\ varphi} }}  ÂÂ$

Perhatikan ini jika kawat berjalan dari lokasi armatur mis. dari x = 0 kembali ke ${\ displaystyle x = - \ infty}  ÂÂ$ dan ${\ displaystyle s}  ÂÂ$ diukur relatif terhadap sumbu kawat.

Jadi, jika angker menghubungkan ujung dua kabel semi-tak berhingga seperti yang dipisahkan oleh jarak, ${\ displaystyle d}  ÂÂ$ , pendekatan yang cukup bagus dengan asumsi panjang kabel jauh lebih besar dari ${\ displaystyle d}  ÂÂ$ , bidang total dari kedua kabel pada titik mana pun di armatur adalah:

${\ displaystyle \ mathbf {B} (s) = {\ frac {\ mu_ {0} I} {4 \ pi}} \ kiri ({\ frac {1 } {s}} {\ frac {1} {ds}} \ right) {\ widehat {z}}}  ÂÂ$

di mana ${\ displaystyle s}  ÂÂ$ adalah jarak tegak lurus dari titik pada armatur ke sumbu salah satu kabel.

Perhatikan bahwa ${\ displaystyle {\ widehat {\ varphi}}}  ÂÂ$ di antara rel adalah ${\ displaystyle {\ widehat {z}}}  ÂÂ$ mengasumsikan rel tergeletak di bidang xy dan berjalan dari x = 0 kembali ke ${\ displaystyle x = - \ infty}  ÂÂ$ seperti yang disarankan di atas.

Selanjutnya, untuk mengevaluasi gaya pada armatur, ekspresi di atas untuk medan magnet pada armatur dapat digunakan bersama dengan Hukum Kekuatan Lorentz,

${\ displaystyle \ mathbf {F} = I \ int \ mathrm {d} {\ boldsymbol {\ ell}} \ times \ mathbf {B} (s)}  ÂÂ$

Untuk memberi kekuatan sebagai

${\ displaystyle \ mathbf {F} = I \ int _ {r} ^ {dr} \ mathrm {d} {\ boldsymbol {\ ell}} \ kali {\ frac {\ mu_ {0} I} {4 \ pi}} \ kiri ({\ frac {1} {s}} {\ frac {1} {ds}} \ right) {\ widehat {z}} = {\ frac {\ mu_ {0} I ^ {2}} {2 \ pi}} \ ln \ left ({\ frac {dr} {r}} \ right) {\ widehat {x}}}  ÂÂ$

Ini menunjukkan bahwa gaya akan sebanding dengan produk ${\ displaystyle \ mu _ {0}}  ÂÂ$ dan kuadrat arus, ${\ displaystyle I}  ÂÂ$ . Karena nilai ? ₀ kecil ( 4 ? ÃÆ' - 10 ^-7 H/m ) maka railgun yang kuat membutuhkan arus pengendaraan yang besar.

Rumus di atas didasarkan pada asumsi bahwa jarak ( ${\ displaystyle l}  ÂÂ$ ) antara titik di mana gaya ( ${\ displaystyle F}  ÂÂ$ ) diukur dan permulaan rel lebih besar dari pemisahan rel ( ${\ displaystyle d}  ÂÂ$ ) dengan faktor sekitar 3 atau 4 ( ${\ displaystyle l & gt; 3d}  ÂÂ$ ). Beberapa asumsi penyederhanaan lain juga telah dibuat; untuk menggambarkan gaya lebih akurat, geometri rel dan proyektil harus dipertimbangkan.

With the most practical railgun geometry, it is not easy to produce electromagnetic expressions for a simple and fairly accurate railgun style. For a more workable simple model, a useful alternative is to use a truncated circuit model, to illustrate the relationship between the driving current and the railgun style.

Dalam model ini railgun dimodelkan pada sirkuit listrik dan kekuatan pendorong dapat ditentukan dari aliran energi di sirkuit. Tegangan pada breech railgun diberikan oleh

${\ displaystyle V = {\ frac {{\ text {d}} (LI)} {{\ text {d}} t}} IR}  ÂÂ$

Jadi total daya yang mengalir ke railgun kemudian hanya produk ${\ displaystyle VI}  ÂÂ$ . Kekuatan ini mewakili aliran energi menjadi tiga bentuk utama: energi kinetik dalam proyektil dan armatur, energi yang tersimpan di medan magnet, ${\ displaystyle B}  ÂÂ$ dan energi hilang melalui pemanasan hambatan listrik dari rel (dan angker).

When the projectile runs along the barrel, the distance from the breech to the armature increases. Therefore, the resistance and inductance of the barrel also increases. For a simple model, barrel resistance and inductance can be assumed to vary as a linear function of the projectile position, ${\ displaystyle x}$ , so this number is modeled as

${\ displaystyle R = R'x}$

${\ displaystyle L = L'x}$

di mana ${\ displaystyle {{\ text {d}} x}/{{\ text {d}} t}}  ÂÂ$ adalah kecepatan proaktif yang sangat penting, ${\ displaystyle v}  ÂÂ$ . Kemudian

${\ displaystyle V = IL'v L'x {\ frac {{\ text {d}} I} {{\ text {d}} t}} IR 'x = I (L'v R'x) L'x {\ frac {{\ text {d}} I} {{\ text {d}} t}}}  ÂÂ$

Sekarang, jika arus penggerak tetap konstan, ${\ displaystyle {{\ text {d}} I}/{{\ text {d}} t}}  ÂÂ$ akan menjadi nol. Resistive losses sekarang berhubungan dengan aliran daya ${\ displaystyle I ^ {2} R'x}  ÂÂ$ , sementara aliran daya ${\ displaystyle I ^ {2} L'v}  ÂÂ$ mewakili pekerjaan elektromagnetik yang dilakukan.

Model sederhana ini memprediksi bahwa setengah dari pekerjaan elektromagnetik akan digunakan untuk menyimpan energi di medan magnet sepanjang laras, ${\ displaystyle L'xI ^ {2}/2}  ÂÂ$ , saat panjang loop saat ini meningkat.

The other half of electromagnetic work represents a more useful power flow - into the kinetic energy of the pro

Source of the article : Wikipedia