# Magnetism-based weaponry

I remember seeing a show on the Science or Discovery channel about a certain type of star, maybe a magnetar, with a powerful magnetic field that would twist and wind over time. Eventually, the field would "snap", returning to a stable state and unleashing a wave of energy in the process.

While the magnetic field around a magnetar is so powerful it disrupts the electron cloud of nearby atoms, would it be possible to scale this effect down to a weapon capable of being used by a single human? Would such a weapon require so much energy for each firing it could only be used once, like an RPG, or would the weapon be useable repeatedly (albeit with a recharge/charge time), such as an AK-47? What effects would the weapon have on the target, the user, and the surrounding environment (e.g., structures, bystanders)?

Feel free to use any level of technology we can currently theorize in your answer.

Edit: Some weapons, such as the railgun, are an impressive next-generation technology, but remain an embodiment of what has made mankind the dominant species on Earth: a "rock" thrower. I am looking for something beyond the next generation of "rock" throwers. Plus, purely energy-based weapons are much more powerful and fun to watch the destruction of.

Wow, $10^8$ to $10^{11}$ tesla. That's a dense magnetic field.

If you want to weaponize this you might be making an electromagnet. We can calculate the requirements to build it.

Here is the equation to calculate the magnetic field produced by an electromagnet: $$B = {{NI\mu}\over{L}}$$

Where $N$ is the number of turns around the core, $I$ is the current through the turns, $\mu$ is the permeability of the core, and $L$ is the flux path.

It's good that you're allowing for any level of technology, because you'll need ridiculous amounts of current, it will have to be in a superconductor. The second magic material you'll need is one with incredibly high magnetic permeability. Basically, this value defines the maximum magnetic field that the material can support. To greatly simplify it, Teslas measure magnetic flux density and materials have a maximum number of flux lines per unit area. I can't give you any ideas on what material to use, permeability changes with the magnetic field strength, it's nonlinear. We don't have data for regular materials with that high of a permeability, maybe they'll figure this out in the future.

You'll also want to have some pretty significant protection if you're trying use this as a handheld weapon. Magnetic fields aren't lasers, they are closed loops. The magnetic field this is putting off is strong enough to rip you apart. That would happen while you're levitating and your brain is filled with light and sound.

Shielding yourself from the weapon would require the same magic-core material, the one with incredibly high permeability. You can't block magnetic fields, you can only redirect them. So the shielding would be guiding the magnetic field from north to south pole on its interior. If the material is too thin or has too low of a permeability, the flux will leak out. The best current man made material saturates at about 40 Tesla. Obviously that's less than the 100 trillion that you need.

Source

• Alternatively, instead of handheld, it could be a kind of very expensive grenade. – Linkyu Feb 11 '15 at 0:35
• @Samuel Do you know any materials that would contain the magnetic field within the weapon, or would these just be theoretical as well? – Frostfyre Feb 11 '15 at 1:05
• @Frostfyre See edits for shielding. – Samuel Feb 12 '15 at 22:44
• @Samuel So I'm going to need a supermagnet beyond anything we've currently developed and a lot of improbibilium to construct a reusable weapon. The weapon might be better as a kind of grenade, as Linkyu mentioned, with an accompanying launcher. The grenade could then wind up the magnetism in transit, rather than storing it next to the user until needed. – Frostfyre Feb 12 '15 at 23:02
• @Frostfyre Oh, the magnetism is generated when current is flowing, so yes don't turn it on until it's on its way. You could, of course, scale the whole thing down to less than a doomsday device. Just sayin'. – Samuel Feb 12 '15 at 23:04

Sounds like a railgun.

A railgun creates a closed electrical circuit between two rails and the projectile. Current flows up the positive rail, across the projectile, and down the negative rail causing the whole thing to behave like an electromagnet. This creates a circular magnetic field around the rails and the resulting Lorentz force propels the projectile.

Railguns have many advantages over chemically propelled (ie. gunpowder) weapons. High velocities are achieved by creating extremely high pressures behind the projectile. These high pressures are due to the very rapid expansion of gases from the heat generated by the gunpowder. The velocities are limited to how much pressure the barrel can withstand, how tight the seal is around the projectile to prevent gas leakage, and how fast your gas is expanding; at a certain point, the bullet outruns the explosion.

In contrast, a railgun does not use pressure but magnetic force. It is not limited by the speed of the explosive, pressures the barrel can withstand, nor the tolerances of the barrel and projectile. It does introduce a whole new set of problems including power delivery, your rails being bent by the magnetic force (there's as much force trying to shove the rails apart as there is shoving the projectile), and your components melting from all the electricity you're pumping through them and the friction of the projectile running along the rails.

High velocity is important in projectiles for three reasons: it increases their range, it makes it easier to aim (less drop to account for), and it makes it pack a bigger wallop. The kinetic energy of a projectile is linear with weight, but exponential with velocity. Making a bullet twice as heavy gives it twice the punch, but fire it at twice the velocity and you deliver four times the punch. Modern kinetic penetrater anti-tank rounds are built around this principle: if you fire a high density dart at something fast enough, it will slam into it with so much energy it will melt the armor so fast it will cause an explosion.

Several militaries are developing railguns. Right now they're quite large and consume a lot of power which means they're mostly for anti-ship or anti-armor purposes. The US Navy demonstrations are impressive. Many Navy ships are undergoing big upgrades to their electrical systems for the expected power requirements (also computers). The US Navy is using a similar idea to railguns to launch aircraft instead of the traditional steam catapults.

Hand held weapons are a way off. The main problem is power density. Until you can make the batteries as light and compact as a clip of ammunition, you won't see railgun battle rifles. What you might see first is a light vehicle mounted railgun-based anti-armor weapon. With the vehicle's power system or an auxiliary generator to call on, you could mount a railgun on a Humvee or Stryker. This would replace the missile systems now in use. A railgun would have a much larger range, more destructive potential, better accuracy, and can carry far more ammunition. This would give mechanized infantry the punch of a tank without the tank. Mostly it would be for bunker-busting, but if an armored vehicle shows up it would be able to destroy it at extreme range.

As an aside, what people often think of as a "railgun" is actually a coilgun. They also use electromagnetic energy to propel the projectile, but retain the barrel and accelerate the projectile using an external magnetic field. Neither the projectile nor the barrel are part of the circuit.

• While I've always enjoyed the idea of a railgun, and find them fascinating, there greatest limitation for endurance in combat comes from the need to supply ammunition. I was looking for a weapon that would rely on fundamental physical properties to do away with the need for a projectile. Still, +1 for taking the time to do the research on a truly impressive next-gen weapon. – Frostfyre Feb 11 '15 at 1:07
• @Frostfyre Much of the weight and bulk of a traditional bullet or shell is in the propellant and case. The actual projectile is small. A railgun doesn't need any propellant so you can carry a lot more ammo. I've seen sci-fi stories which don't even bother with separate bullets, you load a block of metal, the gun shaves off what it needs, and the shock of firing is so great it deforms the metal into a bullet shape, sort of like how a shaped charge works. – Schwern Feb 11 '15 at 1:14
• @Frostfyre In a lot of ways, a kinetic energy penetrator (railgun, anti-tank gun) is how you reliably transfer a lot of energy from you to an uncooperative target a long way off. It's hard to make energy go in a particular direction, it tends to want to dissipate (pesky square-cube law). Lasers work, but it's hard to keep the beam from scattering especially in atmosphere. You can ionize the air to create a circuit between you and the target, a lightning gun, but that requires a lot of power and it's a bit hard to predict. Throwing a well aimed rock has worked for 10,000 years. – Schwern Feb 11 '15 at 1:20
• Rocks and their modern equivalents have been critical to mankind's progression, but I'm looking for the next step, something beyond the next generation. While amazing, the railgun is just a glorified "rock" thrower. Pure energy may be an unstable weapon, but I can't think of anything more powerful or more fun to watch the destruction from. – Frostfyre Feb 11 '15 at 1:37
• @Frostfyre Gotcha. Would you clarify that in your question to guide future answers better? – Schwern Feb 11 '15 at 2:22