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What kind of effect would a tank shell that create plasma on impact have on armour? These projectiles are made up of 3 main parts, a gas canister holding the gas, a capacitor that is used to heat the plasma on impact, & a outer shell to protect it during flight & has a small hole in it to direct the plasma in a specific direction. What effect would this kind of projectile have on armour?

(Note: HEAT rounds aren't plasma based, they use explosive to accelerate solid copper to high speed on impact)

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  • $\begingroup$ worldbuilding.stackexchange.com/q/209240/73451 $\endgroup$
    – OT-64 SKOT
    Commented Aug 3, 2021 at 1:53
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    $\begingroup$ Like with your other plasma based question you're leaving out far too many details. What sort of armor are you talking about? A soldier, MRAP, and tank are all armored but how that armor responds to a projectile differs vastly. How big a projectile are you asking about? Something fired from the main gun of a battleship is going to affect targets differently than something fired from a pellet gun. $\endgroup$
    – sphennings
    Commented Aug 3, 2021 at 3:04
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    $\begingroup$ Plasma of what element, at what pressure and what temperature? $\endgroup$
    – user64888
    Commented Aug 3, 2021 at 3:25
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    $\begingroup$ VTC:Needs Details. Specifically define what you mean by "plasma." I literally mean tell us the chemical composition of the plasma you want us to evaluate. Right now I can't even tell if you're talking about the plasma found in human blood, the chemical state of plasma, or Traveller's PGMP, and none of those are specific enough. Then, explain exactly what armor we're talking about. Leather armor? Plate mail? Ablative? Too few details and too broad a question. $\endgroup$
    – JBH
    Commented Aug 3, 2021 at 3:29
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    $\begingroup$ Come to think of it, having "a small hole in it to direct the plasma in a specific direction" has the side effect of turning the shell into a plasma rocket, causing it to push itself away from the armor it impacts. This might be a good thing if it decelerates the plasma shell enough to prevent it from shattering on impact with the armor. However, in general, it's not clear that the plasma output will stay in one spot long enough to burn through the armor. $\endgroup$ Commented Aug 3, 2021 at 6:33

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Not as much of an effect as you think.

Doing some back of the envelope physics calculations:

  • A M1 Abrams tank shells weigh around 18 kg.
  • Modern capacitors have a max energy density of 9.5 Wh/kg.
  • Assuming all of that shell is capacitor you get a maximum energy released of 171 Wh or 640kJ.

The math would get even worse if you only considered the mass of the projectile.

To put that in perspective;

  • Setting off ONE kilogram of TNT releases 4.6 million Joules of energy.
  • A .50 BMG bullet produces between 14kJ and 20Kj
  • There is more power in chunk of C4 the size of a deck of cards than in your 18kg tank shell.

Real world plasma is very different than the plasma you get in sci-fi. To quote @GrumpyYoungMan;

Plasma isn't special, it's just ionized gas, usually at high temperature but not always (see en.wikipedia.org/wiki/Nonthermal_plasma). Even conventional HE produces plasma (e.g. https://www.researchgate.net/publication/336015137_Study_on_Electromagnetic_Radiation_Generated_During_Detonation which discusses RF generated by plasma during HE detonation) so one could say that HE shells are already "plasma explosives". Any damage caused would be because of the high temperature and kinetic energy of the gas, not the ionization, just the same as regular HE does.

Are you sure you need to do calculations based on your (I'm guessing, limited) understanding of physics? Pretty much every established sci-fi IP that uses plasma weaponry has handwaved the physics and said "Plasma weapons are effective." For instance the super cool bolter round cutout images in 40k don't derive effectiveness from physics. In the game the effectiveness changes as the game gets rebalanced. In the lore it's as effective as the story needs it to be.

My advice is when in doubt do what is cool and trust your audience to care more about your cool story, film, comic, or game than they do about doing physics homework. In fact if someone cares enough about your work to take the time to point how you got your math wrong that's a sign that they care enough about it to obsess over it.

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Not much more different than normal.

Your shells heat up their plasma just before firing. That means the shell is hot, and the maximum temperature of the shell is also the maximum temperature the plasma can take. That means any armor made out of that material would already resist the heat.

Other effects of the plasma could be from its compression: heat expands so we can assume the material you turn to plasma can be under pressure in the shell. Assuming a high pressure upon impact the shell will explode... which makes it a simple hot HE shell. I'm not 100% certain but the expansion rate of the plasma would be limited to the speed of sound meaning it would not be a high explosive and the mass of the expanding cloud would be more important. It would not be a great weapon against other tanks and likely not be any better than either a basic HE round or a specialized incendiary round.

One more option is to use it as a HEAT round. The shell will break specifically on the impact area but not shatter, causing a jet of plasma to get out into the target. The question then is: does the weight and velocity outweigh that of a copper core being liquified by explosives and simultaneously rammed into the target.

You'd need a very very special amount of circumstances to make this worthwhile. A material that expands immensely when it turns to plasma, a material that requires a lot of energy to heat up 1 degree, a method to dump all that energy in the shell quickly or vent the plasma into the shell just before firing and the right material for the shell to contain it while its fired and the right way to break apart.

For a semi-realistic sci-fi such weapons are A-OK, but if you aim for more realism then a plasma shell is not going to be much good. However its still 50 steps ahead of naked plasma bolts that uses magic magnetics to hold it together.

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