I want to write a sci fi story where the main weapons in the setting are rayguns that shoot beams of plasma. The gun works by having a magazine filled with gas, a gas chamber, a chamber that energizes the gas and finally a barrel that closes it into a tight beam. I have a few small questions.

  1. How much kick back would it have, if any? Would the charge make any kickback?

  2. How hot would the weapon get? I had the idea of characters requiring protective gear to wield their gun.

  3. What real world material would be fitting for this gun? (I might just make something up)

  4. What would hot plasma do when it collides with the human body? I had the idea that it would melt the victim's flesh on impact.

  5. What sound would it make?

  6. How could an efficient power system be made for a handheld weapon?

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    $\begingroup$ I think the main realism issue, even with technological hand-waving is how far a small amount of plasma gas can make it through the atmosphere before dispersing. $\endgroup$ – DKNguyen Dec 21 '20 at 22:42
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    $\begingroup$ If it's a plasma beam, that's gonna be the result of a charged particle beam interacting with the atmosphere. Though a handheld CPBW might just be possible. Here are some details: projectrho.com/public_html/rocket/… $\endgroup$ – Mephistopheles Dec 21 '20 at 22:45
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    $\begingroup$ As @DKNguyen said, plasma doesn't "beam" very readily, and is fairly easily disrupted by atmospheric gases. $\endgroup$ – jdunlop Dec 21 '20 at 22:52
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    $\begingroup$ Is this the same question: worldbuilding.stackexchange.com/questions/163079/… $\endgroup$ – Willk Dec 21 '20 at 23:30
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    $\begingroup$ @Liam If you have a forcefield, use that to contain the plasma. At worst you have a plasma sword rather than a plasma gun. That's what Halo does. Personally, I do not buy Halo's magnetic bottling of plasma at long distances. $\endgroup$ – DKNguyen Dec 29 '20 at 20:39

If you want to attack someone with a gaseous weapon, there are several ways to go.

Temperature-based damage: Heating up the gas and then spraying it at someone is not practical. If you use unpressurized gas, there is no good way to spray it far enough to be useful. If you use pressurized gas, it will cool down as the pressure lowers. This is why aerosol cans of body spray feel cool, and why you can get frostbite by spraying an aerosol can on yourself for long enough, and dermatologist use it to remove warts. On the flip side, you can use high-pressure gases as a freezing weapon, although in real life these are much less effective than guns that shoot bullets.

If you spray your opponent with a flammable fluid and light it on fire, or two or more chemicals that create a chemical reaction that is highly endothermic or exothermic, you can burn, freeze, or boil them as you please. This form of weapon is effective enough that it has been used in warfare in the real world in the past: Flamethrowers and firebombs to burn enemies. Bombardier beetles release a spray of two chemicals that react to send an extremely hot spray to irritate anything that bugs them.

Chemical damage: Strong acids or bases can cause irritation or even severe injury to a person that they're sprayed on, but the ammunition is challenging to store. Poison is much more effective. All you have to do is find a poisonous or venomous plant, animal, fungus, bacteria, or other life form, mix the active ingredients into an aerosol or liquid, and shoot it at somebody you don't like. This could also be effective for non-lethal weapons. Police forces use lachrymator gases to commit war crimes against peaceful protesters for riot control. And putting a bunch of crushed-up habaneros and poison ivy in the tank of your super soaker probably won't kill someone, but they might wish it had.

Fluid weapons can be delivered with hoses or aerosols. You need some way to pressurize them, but this is not difficult. The ammunition could come pre-pressurized, like canned aerosol cheese or paintball gun CO2, or the pressure could be generated by hand like toy water guns or BB guns.

Gaseous weapons have lots of drawbacks. If you use it against somebody who is too close to you or inside a sealed building with you, you will be exposed to whatever your attacking them with. They have a shorter range than many firearms. They are harder to aim precisely. Bullets are only dangerous while they are moving quickly. The chemicals you use might linger for a long time, which means they are a bad choice for weapons to use for home defense.


Research was done many years ago in the US on a weapon like effect that might suit your purpose.

(I think the late 90's early 10's) It would take some time to dig up the papers.

Basically the researchers were looking at a laser weapon that was tuned to the specific frequencies most likely to be absorbed by air molecules (oxygen and nitrogen primarily I think). In any event this is the opposite of what most laser researchers would attempt to do but these guys were thinking a little outside the box.

The idea was that the weapon could be pointed at a target and fired. Laser light would then be absorbed along the path the laser took to the target by air molecules which would then be turned into plasma. Since plasma is electrically conductive the intent was to use the briefly functional line of plasma between the target and the weapon as the conduit for a burst of electrical current which would strike target.

If you could modulate the current correctly you might (I really don't know) be able to induce a Taser like effect on the target, possibly a lethal one. You could also potentially fry any electronics they were carrying.

Downsides? Probably short ranged and it might be possible to insulate yourself (again I don't know).

A second weapon; Looked at the possibility of striking a target (again with a laser) but this one was fired as a very short pulse designed to vaporize something on the surface of the target. The result, a small brief plasma pulse. It could be skin or clothing or any physical surface. It didn't matter. The idea was that the first pulse creates a small ball of plasma on the targets surface. Importantly the pulse itself is not particularity damaging, if you were struck in the face the outer layer of your skin would vaporize, little or no serious internal damage would be caused at all.

The key? a second, precisely timed laser pulse is fired immediately after the first one. This second shot impacts the plasma (from a human perspective the shots are effectively simultaneous) compressing the plasma into the target.

Most of the plasma, compressed under the force of photons traveling at the speed of light has no-where to go except directly towards the target. This induces a kinetic impact effect. Like the impact of a rifle bullet. All that kinetic energy has to go somewhere and in this case its into the target!

Plus side? In theory virtually any surface will serve as the target for the first pulse, the effect can't be shielded against by solid matter. Downside, complicated math, everything has to be timed to perfection for each shot at varying ranges. So you would need a complex targeting calc to be done by the weapon's targeting system as you pull the trigger.

Hope this helps with some ideas. Both would sound a bit like a sudden electrical discharge or pistol shot (I think) because both disrupt the air in passing and release their energy almost instantly.

One other big downside - the first weapon wouldn't work in a vacuum and would probably have to be 'tuned' for every new planet you went to.

Hope this helps.

  • $\begingroup$ Notice, that when you can print conducting lines into mid-air- lots of other concepts become viable. Why have clunky metal rals for a railgun? Print some glowy lines, charge and be done. $\endgroup$ – Pica Dec 22 '20 at 15:34
  • $\begingroup$ So basically, either a beam that energizes particles in the air or a combustion beam. Those both sound like ideas I'd be interested in $\endgroup$ – Liam Dec 23 '20 at 20:15
  • $\begingroup$ I think the principal is the same in both. Use a laser beam to generate plasma. In one case out of air to form a circuit. In the other a brief burst on the surface of a target. Unless you count the plasma itself as 'combustion' then neither really 'combusts' anything. In the first case electrical current may heat up/combust the target as a side effect. In the second there might also be some combustion as a side effect of the plasma 'burst/ball' being physically driven into the target by the second laser pulse but as I recall (and I could be wrong) there was also a kinetic effect as well. $\endgroup$ – Mon Dec 24 '20 at 1:03
  • $\begingroup$ One other thing about the second 'weapon' which just occurred to me. As I noted the two pulses used to generate damage are effectively simultaneous. I have no idea of the timings concerned but they could easily be in milliseconds apart (or even faster) - they have to be fast for the device to work. However there's nothing (except power constraints) stopping the weapon from firing multiple twin pulses as once. So you could say fire 20 pulses for 10 'impacts' as one round. Or 20 or 50 etc. That might well ramp up the damage because you'd get multiple strikes on the same impact location. $\endgroup$ – Mon Dec 24 '20 at 1:22
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    $\begingroup$ You could possibly combine both in one weapon. The primary weapon is the 'pulse' laser that creates a burst of plasma on the targets surface and the secondary is a backup module (attached like a grenade launcher to a modern assault rife) for use in boarding ops and such. So anyplace there is air - e.g. once your are inside you have a weapon that can stun as well as knock out electronics. $\endgroup$ – Mon Dec 24 '20 at 23:12

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