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Assume a fairly futuristic scenario where we can deal with the energy requirements of handheld laser weapons and the realistic creation of plasma ammunition etc.

From what I understand a plasma gun will shoot a ball of plasma like a projectile, which provides a little bit of kinetic energy and "burns" its target. A laser gun is just a continuous beam of energy that burns the target for as long as you fire it.

What exactly would be the advantages of one over the other?

Lasers obviously don't burn after you stop firing, but they are more "instant" (traveling at the speed of light rather than an ejected projectile). Do they burn better than plasma? They are also silent and invisible.

Also, would a plasma gun hold any advantage over regular kinetic weapons? Would they have less of a kinetic impact? Less instant kill potential? Is the burn effect worth it?

I've tried Googling a lot for comparisons from a somewhat scientific perspective, but I usually just end up finding threads about people comparing the stats of plasma vs laser guns in a specific game or something, which obviously is not what I am after - if anyone has got useful links for me to read I'd be happy about that too.

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    $\begingroup$ Related:Pros and Cons of Laser and Projectile Weaponry. Not much in there about plasma, but some good answers about laser guns. $\endgroup$ – DaaaahWhoosh Aug 11 '15 at 13:36
  • $\begingroup$ How hand-wavy and implausible of an answer are you expecting? For example, if someone "invents" a somewhat-stable moving magnetic field "bubble", maybe they could fill it with plasma and project it through air. Supposing such a thing could exist, plausibly it would have the effect essentially of vaporising (well, in fact plasma-ising) everything in its path for a certain time/distance until the bubble collapses, releasing the plasma in a final explostion. Hopefully at sufficient distance from the weapon that the user isn't too seriously inconvenienced. $\endgroup$ – Steve Jessop Aug 11 '15 at 21:07
  • $\begingroup$ ... such a weapon could be devastating (albeit not always tactically the right tool for a given job) depending on the total energy embodied in the plasma, but that's not to say plasma weapons have these properties, it means one completely made-up thing has those properties. A different made-up thing, or the best plasma weapon we could build with current plasma-generation and containment technologies, would have completely different properties as a weapon. You posit "plasma ammunition" without saying what that actually is. $\endgroup$ – Steve Jessop Aug 11 '15 at 21:09
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    $\begingroup$ Plasma weapons and laser weapons are equally poor choices relative to a chemically propelled solid slug. $\endgroup$ – Russell Borogove Aug 11 '15 at 22:35
  • $\begingroup$ I'm trying to flesh this question out a bit to avoid starting a new thread. Rick points out the issues of atmosphere. Would this be a gun that would work better in areas without atmosphere? Also, what keeps the high heat of a plasma or laser gun from igniting artificial atmosphere? O2 is combustible and anything superheated in a contained space pumped full of O2 seems like a bad idea. Patients in hospitals have lit themselves on fire (including breathing that directed fire right in through their noses) due to jones-ing for a smoke and lighting up in their rooms. $\endgroup$ – whitepawn Oct 19 '15 at 20:21
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Plasma weapons are a popular SF concept that just won't go away. They are encountered in such diverse places as the original Star Trek TV series, and the Babylon 5 TV series. They play the role of a futuristic flame-thrower.

Their main draw-back is that they won't work.

Plasma is the so-called "fourth state of matter", and is basically hot air. When we say something is hot, we're actually talking about the speed with which its individual component atoms wiggle around. Room temperature gas moves at about 500 m/s. Obviously, plasma is really really hot. That is, it is a gas heated to temperatures comparable to the interior of a star or the center of a thermonuclear explosion so that all the atoms are ionized. Unfortunately, according to the virial theorem, the plasma wants to equalize its internal pressure with the external, i.e., it wants to expand into a diffuse cloud of nothing. And since it moves really really fast, this means that after the plasmoid travels for one second, its diameter will be approximately five thousand kilometers, i.e., it has dissipated into nothing.

More cool info here

So I'd go with lasers. :) For extra oomph, make them gamma ray lasers.

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    $\begingroup$ Just like flame throwers don't work, eh? $\endgroup$ – Aron Aug 11 '15 at 13:10
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    $\begingroup$ @DaaaahWhoosh, assuming what I wrote is not enough to persuade you of unfeasability, what would it take to persuade you? $\endgroup$ – Serban Tanasa Aug 11 '15 at 21:46
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    $\begingroup$ @Andrey, if you know how to build a bullet size shield capable of holding million degree plasma, I know some fusion power people who wanna talk to you $\endgroup$ – Serban Tanasa Aug 12 '15 at 1:24
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    $\begingroup$ @DaaaahWhoosh The point of the Virial theorem is that any kinetic momentum you try to impart onto your plasma is dwarfed (factor 10000 or so) by the kinetic momentum of individual particles within the plasma. So it just goes boom. $\endgroup$ – Serban Tanasa Aug 12 '15 at 13:42
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    $\begingroup$ @Aron flamethrowers don't throw flames, they throw liquid and sticky napalm which is on fire and then keeps burning once it sticks to the target ;) Movie flamethrowers are just gas burners (for obvious safety reasons) and would be much less effective... $\endgroup$ – peufeu Nov 14 '17 at 11:34
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The open-source game UFO:AI has a plausible-sounding design for both plasma and laser weapons, and the in-game description has a very detailed hard sci-fi explanation about how they work. All the advantages and disadvantages of plasma and laser weapons are presented in detail, both in the descriptions and their in-game functionality, although the later is a little bit abstracted. A very powerful late-game weapon is actually superior to the alien's plasma rifle, as it's a normal kinetic weapon with a projectile including a very little amount of plasma, designed to burst after entering the target, working both as a shaped charge to punch through armor, and as a very advanced version of the real-life expanding bullets.

The plasma weapons involve a solid protective shell which is designed to burst after traveling for a short while. They have a small range, because despite the projectile traveling fast the plasma eats through the casing very fast, and due to its lighter weight the accuracy is also lower than of traditional firearms. What it excels at is its high stopping power. Whoever is hit, feels the pain immediately.

The laser rifle uses a type of chemical laser, has very high accuracy and a long range, no recoil, but with the added problem of having no sudden impact, therefore a lower damage, and that they require some time on the target, effectively reducing the damage due to the shooter's inaccuracy as the beam might wobble on the target.

Basically, compared with traditional firearms, the plasma and laser rifles actually represent two completely opposite directions, instead of being almost interchangeable with each other compared to the traditional firearms.

I'm not suggesting to completely copy these designs from the game I mentioned, but it might be worth taking a look at, as the developers obviously put a lot of though and research into it.

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  • $\begingroup$ "normal kinetic weapon with a projectile including a very little amount of plasma" actually sounds like the very real RPG 29 rounds used in modern warfare. It is one ofthe few munitions capable of penetrating the front armor oft he M1 series tanks. $\endgroup$ – pojo-guy May 23 '17 at 1:39
  • $\begingroup$ @pojo-guy : isn't the RPG more about molten copper than actual plasma? Nevertheless, the example given is not a shoulder-launched RPG, but a normal rifle round. $\endgroup$ – vsz May 23 '17 at 18:21
  • $\begingroup$ You are correct, showing the importance of checking sources. It is an incremental rather than quantum step from molten copper to plasma (think plasma cutter used by welders) though, and some conceivable incremental steps to miniaturize that to a 50 caliber "bullet-like" form. $\endgroup$ – pojo-guy May 23 '17 at 20:59
  • $\begingroup$ Since high power chemical lasers have exhaust products like Deuterium Flouride exiting the exhaust vent at several thousand degrees, you may want to reconsider that as a man portable weapon. $\endgroup$ – Thucydides Nov 14 '17 at 11:13
  • $\begingroup$ @Thucydides So, one end works as a laser, the other as a short-range plasma-thrower. What's the downside? $\endgroup$ – Alice Nov 14 '17 at 14:19
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While shooting plasma as projectiles doesn't work, using lasers to turn the air into a plasma has interesting applications in weapon design.

If you want an actual laser weapon it's advantageous to deliver as much power to the target as possible. Unfortunately, when light travels through air ti interacts with it causing heating and light scattering. Once the beam has high enough power density, it will heat the air into a plasma, which interacts with the light much more strongly. This effectively creates a maximum power delivery to the target as any additional power output by the laser just goes into heating the plasma.

However, the plasma does create another possible energy delivery mechanism, as plasma is conductive. If one fires two high powered lasers at a target, they could be used as wires in a high powered version of a taser, where rather than being a non-lethal weapon it's an insanely high powered tank exploding weapon.

However, due to the natural tendency for air to breakdown into plasma under high electric fields it's likely that beams would have to be far enough apart that the weapon could not feasibly be considered a handheld weapon. (unless it's being wielded by a giant or a mech suit.)

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Self contained plasma bursts are possible, as Randy Curry recently proved. Now his experiment only went two feet, but it's proof of concept.

https://www.youtube.com/watch?v=T5sIPJL_6F8

Other problems with Plasma Weaponry might still hinder development, but plasma dispersion is not one of them.

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For plasma weapons one would probably be shooting either skyrmions (knotted magnetic lines that the plasma follows or a very past non-contained plasma (see the SHIVA start project). In either case, the relative mass is less than that of a bullet, the "net" kinetic energy involved would either be small or transfer in-efficiently, the compression and then sudden expansion of the plasma would be the main damage effect. This can be easily done today (though it is against the Geneva convention on sub 12.5mm expanding or exploding bullets) so there seems to be little advantage (beside possible weight and logistics depending on the power source and ammunition).

Lasers are different. First, it depends on how you wish to cause damage. As far as I can find the most effective when power is not an issue is a rapidly expanding plasma that is generated by a laser. The US did testing on both lethal and non-lethal versions (Pulsed Energy Projectile (PEP) and Pulsed Implosive Kill Laser (PIKL)). Such a system has little recoil (mostly from expanding air in-front of the muzzle) and has the same advantages and disadvantages of any laser system (logistics mostly, with the weather being an issue fro targeting).

Overall there is very little use for a small scale laser weapon or plasma weapon. Most kinetic weapons today can perform the same and have less significant draw backs. Logistics is the biggest win and so in cases when that is paramount then it would be better to have a laser or plasma weapon, and since a plasma weapon and laser weapon are the most effective when having similar terminal ballistics (photistics?) the winner between them would be plasma due to its (most likely) superior inflight characteristics (less susceptible to weather effects). And while kinetic weapons may change the way that they acclerate (powder, electro-magnetic, gravity, etc.) they are still overwhelming more effective.

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    $\begingroup$ Welcome to WorldBuilding Dave! If you have a moment please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$ – Sec SE - clear Monica's name Apr 8 '18 at 8:47
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In favor of lasers:

  • The output of a laser is massless; all you need is the energy storage, no material for your "ammunition".
  • Lasers move at the speed of light; you cannot dodge a laser (though depending on the power and wavelength you might be able to find cover before you're permanently damaged)
  • Lasers are unaffected by wind and pure range.
  • There's no theoretical limit to the power output of a laser; plasma has to be contained or buffered in some way which limits the power output.

In favor of plasma:

  • Adding mass means there is some heat transfer by conduction and convection, instead of merely radiation; Whenever there's matter to readily conduct or convect energy, the transfer of that energy into your target tends to be more efficient.
  • Plasma, having to be magnetically "bottled" to travel out of the weapon any practical distance, would be better buffered against the transfer of energy to the surrounding air, while a laser would have to "burn through" the air and anything it contained (fog, dust, smoke) which is the major source of attenuation of energy.
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I'm always surprises at people going "plasma cant work!". Imagine this: "I've got this great idea for a tank penetrator. You use something heavy that liquidises under pressure and shape something around it so that this cuts like a heated waterjet through the armor".

"yeah", says his buddy, "but lead will deform upon firing and using some kind of magnetic system to keep it together, pressurise it and aim the jet won't work!"

To which people even during the world Wars replied, "we could also use something less outlandish like the materials we have lying about for a hardened shells that does exactly that".

Heat up the plasma while in a container like VSZ suggested in his post. Use a material with a high temperature resistance like Tungsten, or since you arw talking future tech use a Graphene shell (withstands a bit more than the surface of the Sun) and encase that with some insulator since Graphene has this nasty habit of being one of the best heat conductors known to man and losing heat is so annoying. It does make it easier to heat up the plasma in the first place. Once it hits and the plasma is released plasma has this nasty habit of expanding rapidly. We usually call this an "explosion". To maximise that, engineer the capsule to break open only at the impact site, creating an instant shaped-charge sending Hot plasma through the opponent.

As for laser weapons, Atomic Rockets (http://www.projectrho.com/public_html/rocket/sidearmenergy.php) points out how lasers need to be very focused to work and lasers are harder to keep together across a distance than people think when talking about killing people with them. The best method they come up with is firing 1000 laserpulses in about 0,01 seconds. Each pulse is a joule or more, and turns the surface of your target to vapor or plasma. This plasma expands rapidly in a miniature explosion, most of which goes directly in the laserbeam. To prevent the plasma from soaking up energy meant for the target you use the pulses.

Each miniature explosion rips part of the material around it away, causing large holes in your target each pulse. However this is unlikely to be silent. Your PC isnt silent because it needs cooling down, you are blowing away massive amounts of energy and even at its peak you have to assume no more than 70% to 90% of the energy is used for the laser and the rest is waste, and thats extremely generous as most estimates are more around 50%. Theres also the problem that you turn everything in the laserpath to plasma, including any dirt on the lens which will damage it unless its from a high-strength and -heat resistant material, but it wont be silent.

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