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I'm interested in the technical feasibility of a rifle that fires a lightning bolt.

Typical lightning requires a large difference in electrical potential, and something that prevents equalizing this difference. In lightning storms the ground and clouds (in normal cloud-to-ground scenarios) the "polarities" of our difference in charge. The air itself insulates the exchange of electricity to balance out these charges.

Lightning produces "leaders" prior to the actual flash of electrical discharge we see. Leaders are Channels of ionized air that effectively seek out shortest path (and produce the zig-zag pattern of the bolts).

Wikipedia's article on Lightning tells us that normal negative lightning contains "carries an electric current of 30,000 amperes (30 kA), and transfers 15 coulombs of electric charge and 500 megajoules of energy" it also mentions that positive lightning is about 10 times this powerful.

Questions the rifle needs to overcome:
The rifle would have a difficult time producing an opposite charge in the target, as opposed to just holding a huge capacitive type charge. Will this matter?

Would the rifle be able to use a short range "laser" that would produce a straight channel of ionized air to the target?

Would this channel be sufficient to keep the lightning on track to hit the target instead of jumping to other nearby grounding sources?

Given the absolute best capacitors/batteries/etc. can a rifle sized/weight object contain the energy of a negative bolt? Positive bolt? I'm assuming cost is no problem here but feel free to ball park a cost.

Could this rifle switch between negative/positive bolts like the weapons in sci-fi movies (i.e. "set your lasers to stun")?

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    $\begingroup$ I think a lightening rifle would be more dangerous to the wielder, than anything, unless it's like a taser. $\endgroup$ – bowlturner Aug 11 '15 at 16:43
  • $\begingroup$ Just don't wear steel-toed boots! $\endgroup$ – Serban Tanasa Aug 11 '15 at 16:53
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    $\begingroup$ Forgot to ask for best lightning rifle name in my question! Zeus, Thor... so many possibilities =D $\endgroup$ – Culyx Aug 11 '15 at 18:11
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The US has already done it.

At the moment, the gun shoots lightning down a laser beam. Essentially, what it does is it uses a laser to carve an electromagnetic pathway through the air, so that the high voltage beam will use it.

A very very very short pulse of laser that's high intensity will be shot, and that creates an electromagnetic field around itself so powerful that it rips out the electrons from the air, creating a pathway of plasma.

Since plasma is a better medium than the air around it, the lightning travels through that instead.

However, this is not a very feasible weapon. Not only is a ton of hardware required for it, the shelf life likely isn't very long. Compared to a normal gun, which has bullets that fire straight, easy maintenance and long shelf life, this gun is likely to melt itself after a while, and would be hard to maintain.

I couldn't find the actual technical aspects of the US designed weapon (I doubt they'd release those to the public anyways), but I'll try to answer your requirements anyways.

The rifle would have a difficult time producing an opposite charge in the target, as opposed to just holding a huge capacitive type charge. Will this matter?

It won't matter since you don't need to produce a charge in the target. You just provide a path.

Would the rifle be able to use a short range "laser" that would produce a straight channel of ionized air to the target?

Yes. That's exactly how it's done.

Would this channel be sufficient to keep the lightning on track to hit the target instead of jumping to other nearby grounding sources?

Yes.

Given the absolute best capacitors/batteries/etc. can a rifle sized/weight object contain the energy of a negative bolt? Positive bolt? I'm assuming cost is no problem here but feel free to ball park a cost.

It's been done, so with enough hardware, yes, either the negative or positive, but I'm not sure which - I'm pretty sure lightning is just... lightning. Also, very very expensive.

Could this rifle switch between negative/positive bolts like the weapons in sci-fi movies (i.e. "set your lasers to stun")?

Probably not. Lightning the way you described it will never be able to "stun" (Too much power involved) - you're always going to be in kill mode, regardless of negative/positive mode, so why bother swapping to a more expensive mode?

It's been noted that this weapon is easily disrupted by insulation. To that, I point towards Samuel's answer for a more effective version of the gun which provides it's own grounding path.

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  • $\begingroup$ I didn't so much mean stun as dial the power up or down from one type of lightning to the other (check wikipedia on positive and negative lightning) but from the sounds of things that is completely doable with this technology. $\endgroup$ – Culyx Aug 11 '15 at 17:44
  • $\begingroup$ @Culyx I guess you have your answer then. Although the way you described it (one from source -> ground, the other from ground -> source) would imply that one of the types requires a connection from target -> gun which is probably impossible. $\endgroup$ – Aify Aug 11 '15 at 17:46
  • $\begingroup$ I think its a semantic issue in my question; "ground" in this case meaning actual earth ground not "grounded" in the electrical sense, the current also goes negative to positive of course, but the position of the negative charge (whether in the clouds or accumulating in the earth) is the big difference $\endgroup$ – Culyx Aug 11 '15 at 18:10
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    $\begingroup$ So I stand by my comment then. Positive lightning happens to be more powerful because it bridges a larger gap. Nothing innately about "positive" or "negative" makes it more powerful. $\endgroup$ – Tim B Aug 12 '15 at 19:41
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    $\begingroup$ @Aify Oh well, if you think that that's proper formatting (a wall of two liners and unformatted lists) then take a downvote for lack of readability. $\endgroup$ – David Mulder Aug 18 '15 at 0:54
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The basis for this technology already exists, it is called an Electrolaser and it works as follows:

You fire a laser into the air, and take advantage of the fact that lasers diffuse in air by stripping electrons free of any atoms that they come into contact with. This creates a directed channel of free electrons, also known as Plasma, which is one of the best electrical conductors in existence. You then create a surge of electricity at one end of the plasma channel, which conducts down said channel like it was a live wire.

Applied Energistics is the primary US contractor working on this technology, and they are currently working on designs for everything from portal denial (a stationary system that can remotely shock people trying to pass through a door) to a handheld variant. Another company working on the same sort of thing is HSV Technologies.

The voltage requirements to replicate lightning with this system are well known, and are currently around $10^8$ to $10^9$ volts. Right now, this is a tremendous amount of power, but can be obtained by using step-up transformers to trade current for voltage. (Ideal 'stun gun' uses high voltage low amperage anyway) Seeing as lightning has a typical voltage of only $10^8$ volts, this is to be expected. However, you can dial back to only ten to twenty thousand volts if you are aiming it at a person with intent to stun, not kill. That's easy, we put that in hand-held stun guns all the time.

The challenge remaining is not so much 'can we produce a strong enough voltage to drop someone.' Plasma is a reasonably good conductor with very low resistance. Much of the energy released into the beam will strike the target. The challenge is 'can we power a strong enough laser to create the plasma channel.' Again, the answer is 'yes.' The power of the laser would dictate the range it could fire before completely falling apart, but you could throw a strong enough laser for a 'pistol-range' shot pretty easily. You aren't trying to burn anyone with the laser, just ionize the air. It doesn't take too much to do that.

To address a few of your other questions.

There would be a small amount of scattering, but electricity prefers to follow the path of least resistance...and plasma is an awesome conductor.

There is no such thing as 'positive' or 'negative' electricity. Electricity which is the movement of electrons, which only carry a negative charge. If you want something that behaves like electricity but has a positive charge, you need positrons. But then you are playing with antimatter, thus boom. If you want to vary the lethality of the bolt, adjust the voltage or amperage (an amperage between 100 and 200 mA will stop your heart). It's the same way you can taze someone to disable them, or electric-chair someone to kill them.

A few notes of caution...

Be careful using such a weapon during a storm, as the Plasma Channel created is very friendly to natural lightning, and may invite a bolt to jump down into the channel.

Be careful using this weapon near high voltage power lines, the presence of such a strong conductor may cause power to arc out of the lines and jump into the plasma channel.

Ensure the weapon is well insulated so that it cannot ground itself out through you, and must ground itself through the target.

Ensure proper timing of the laser/electrical pulse, otherwise the beam may not have sufficiently ionized the air, and the surge of electricity will behave according to physics (and might jump back at the gunner).

All that taken into consideration, here are a few other things an Electrolaser is capable of.

Burning out electronics, including the ignition and alternator systems of an automobile. To control natural lightning strikes: there are designs out there for firing a high power laser through a thunderhead to 'aim' natural lightning strikes at targets.

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  • $\begingroup$ Negative and Postive lighting are indeed both lightning, the difference is in their origin. Negative lightning starts at the bottoms of clouds and jumps to near ground targets (which accumulate under the storm), positive lightning is a large positive charge in the tops of large storm clouds that jumps to negative ground targets. The main difference just being the energy differential and the "direction" negative-to-positive that the bolt travels. $\endgroup$ – Culyx Aug 11 '15 at 17:42
  • $\begingroup$ @Culyx Point. However, that is a question of how the electrical differential is formed. You are still moving electrons around, which are always negative in charge. That's...what electricity is. I edited my post to clarify that. That said, the 'can I use positive lightning to stun someone and negative to kill them' remains impossible. $\endgroup$ – guildsbounty Aug 11 '15 at 17:54
  • $\begingroup$ I used "stun" since they only ever mention that in stuff like Star Trek, I was under the same impression you are; the two settings are kill and super kill. =P $\endgroup$ – Culyx Aug 11 '15 at 18:08
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    $\begingroup$ @Culyx The 'settings' are, as I mentioned, determined by voltage and amperage. You can 'turn the gun down' to make it not hit them as hard so that it could range from 'disciplinary shock' to 'smells like burnt ham.' $\endgroup$ – guildsbounty Aug 11 '15 at 18:16
  • $\begingroup$ Aside: Electricity is electrons moving around? Not quite. Yes, current requires the movement of charged particles, which tends to be electrons because they are so much lighter and more mobile than heavy positively charged ions – though ions are important charge carriers in chemistry and esp. biochemistry. Nevertheless, electrons are surprisingly slow – on the orders of millimetres per hour in an ordinary wire. A more useful model: signals and power are transmitted along via electric fields which propagate near the speed of light, not through individual electrons. $\endgroup$ – amon Aug 11 '15 at 21:34
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You need to provide a grounding path.

The other answers are on the right track. However, they're missing an important component. They rely on generating a path from the gun to the target and the return path through the ground. This is folly, because all the person needs to do is insulate themselves from the ground. The obvious answer and addition my answer brings to to create two plasma paths with the lightning gun.

Call it the Double Tap.

If you create two paths from the gun to the target you have effectively created a complete circuit with the target. You can now send variable currents up one path, through the target, and down the return path. You also have the option still to use both paths for sending current and using the ground as a return path or you can use one to the target and one as a return path aimed at the ground further away from you.

The rifle would have a difficult time producing an opposite charge in the target, as opposed to just holding a huge capacitive type charge. Will this matter?

This doesn't matter. The target is simply a part of the complete circuit. You don't need to rely on them providing a charge.

Would the rifle be able to use a short range "laser" that would produce a straight channel of ionized air to the target?

This rifle would use two lasers to create a complete circuit with the target through the air.

Would this channel be sufficient to keep the lightning on track to hit the target instead of jumping to other nearby grounding sources?

No grounding source required! You provide the grounding path.

Given the absolute best capacitors/batteries/etc. Can a rifle sized/weight object contain the energy of a negative bolt? Positive bolt? I'm assuming cost is no problem here but feel free to ball park a cost.

You would use capacitors for this, but they can only contain the energy, you'll need to increase the voltage after it leaves the capacitors. There are no capacitors which can contain both the energy and the high voltage. This is because a very high voltage requires a significant amount of insulation between plates. You can fit more surface area inside a capacitor when it has much thinner plates (lower voltage).

Could this rifle switch between negative/positive bolts like the weapons in sci-fi movies (i.e. "set your lasers to stun")?

Yes, though there is no difference to the target. A positive bolt vs a negative bolt just describes the origin of the bolt from clouds to Earth and in this case the direction a charge flow through the target. It doesn't matter which direction a few amps goes through a person, it does the same damage. This particular gun, because it supplies the return path can therefore adjust the current through the gun and target from a lethal bolt to a stunning shock.

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  • $\begingroup$ You've... described a Taser? $\endgroup$ – mskfisher Aug 11 '15 at 20:00
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    $\begingroup$ @mskfisher The one difference being that a TASER electroshock gun shoots two wires into the victim, while this makes two air ion channels. $\endgroup$ – Damian Yerrick Aug 11 '15 at 21:15
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    $\begingroup$ @mskfisher Indeed, it's a TASER that creates its own conduction paths at light speed (no wires required). $\endgroup$ – Samuel Aug 11 '15 at 21:33
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    $\begingroup$ Hmm, you have a problem here - no insulation between the channels and the tiny air gap between them is unlikely to be enough. There is a high likelihood that it will just jump between them and straight back into your gun. $\endgroup$ – Tim B Aug 12 '15 at 19:01
  • $\begingroup$ @TimB Why make it tiny? You get 33 kV/cm for air. It's excellent insulation. Put 10 cm between the lasers and we can charge to 330,000 volts without worrying about dielectric breakdown in the air. Though the current we'd have to throw down those two very low resistance channels would have to be insane to get the voltage that high. $\endgroup$ – Samuel Aug 12 '15 at 19:08

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