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Information:

The plasma cannon is a weapon, that fires a continuous beam of plasma (with this, it can be sustained by the weapon, while it's fired) which is confined by a helical magnetic field. It's usually used as a cannon (hence its name), but with a sufficient battery technology, it could theoretically be used as a handheld weapon.

And it has a great tactic against magnetic fields, that is demonstrated in the following situation:

  • A challenger appears with a powerful magnetic field.
  • The cannon detects the magnetic field and creates an electromagnetic field that attracts it. enter image description here
  • When, everything is arranged in the way it should be, the plasma cannon fires, at this point the other magnetic field not only doesn't deflect the plasma, but guides it into the magnet.

The challenger will probably get's the answer to his question in hell.

Questions

  • What are the flaws of this concept? (I'm pretty sure that it has a ton of them)
  • Is it possible to flip the pole of the other magnet?

Things to consider

  • Let's just assume that the energy requirements can be handwaved.
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  • $\begingroup$ I would use an alternating current electromagnet to make my magnetic shield. $\endgroup$
    – Willk
    Feb 22 '17 at 19:21
  • $\begingroup$ @Will This is, why I wonder, whether the pole can be flipped back if that's the case. $\endgroup$
    – Mephistopheles
    Feb 22 '17 at 19:26
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    $\begingroup$ They might be able to deflect the plasma, but their giant magnet does NOTHING to shield them from the sheer radiant heat of the plasma. To make a plasma (in air) that's got enough destructive force to be a good weapon will require so much energy, that even just the radiant heat will fry anyone nearby. Just a thought... :) $\endgroup$
    – Samwise
    Feb 22 '17 at 22:28
  • $\begingroup$ It's important to keep the purpose of a weapon in mind. To deliver sufficient energy to a target to damage it. A sustained discharge plasma cannon delivers that energy over a (relatively) long period of time. This is why impulse delivery systems $\endgroup$
    – pHred
    Feb 23 '17 at 3:20
  • $\begingroup$ ... damm edge screen, dont get one! ... are preferred (railgun). The projectile is heated and accelerated until it becomes a plasma. All that energy is then delivered to the target with none of it lost to sustaining the plasma. In or ex atmo also makes a huge difference. In addition your plasma cannon may well be creating magnetic fields on the order of many T. The effect of these on the brain is not well understood but the consesus is that at sufficiently high levels it would at least be like undergoing ECT. $\endgroup$
    – pHred
    Feb 23 '17 at 3:28
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What's to keep the target from manipulating their magnetic field?

Note that there are a number of reasons that could prevent that but you should know the answers if you are using it as a plot point.

How far can the plasma get before it cools down enough to condense back to a normal state?

That will probably be relative to the speed the plasma travels. Unless you can contain the heat in the beam, the cooling rate in a vacuum (vacuum assumed) will be fixed.

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  • $\begingroup$ According to MethPat, sustaining plasma state requires less power, than creating it, thus if electricity, somehow still can reach it, it might wouldn't be a complete garbage on longer ranges.(youtu.be/Zq1aPOunsFA?t=551) $\endgroup$
    – Mephistopheles
    Feb 22 '17 at 19:33
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Flaws:
1. A bullet would probably be cheaper.
2. The energy concentration required to ionize and superheat gas could probably be used for something more productive. Like propelling a bigger mass.

Despite what the movies show, magnetic fields are only really useful when dealing with charged particles and ferromagnetic objects. NOTE: PARTICLES. A lead bullet is neither, and would simply go straight through a magnetic field. Unless the field is sufficiently strong as to deflect high speed paramagnetic objects, in which case, the user better be safely inside a shielded suit or they'll get ionised.
In any case, the shield is easier to overcome by simply increasing the calibre of bullet used, rather than using exotic technology.

The alternate approach is, as you have suggested, flipping the magnet. Do it fast enough, and you get an electromagnetic transmitting antenna. Properly focused, this gives you a microwave transmitter, which will give you a better energy transfer per joule supplied than your plasma cannon. Something like the US military's Active Denial System.

What you've suggested is similar to Tesla' Teleforce or "death ray". To my knowledge, nobody has been able to make it work.

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    $\begingroup$ Starts to read the linked page blah.. blah blah ...accelerated pellets or slugs of material to a high velocity...bl.. wait? So the Teleforce was just an overmystified railgun?! $\endgroup$
    – Mephistopheles
    Feb 23 '17 at 15:12
  • $\begingroup$ @RedactedRedacted: Disappointing,ain't it? After all the hype too...And his version still doesn't work $\endgroup$
    – nzaman
    Feb 24 '17 at 6:35
  • $\begingroup$ @RedactedRedacted: Also, it's more of a particle accelerator than a rail gun. I didn't know the difference either till I came to this site. Still the vacuum requirement killed it as a weapon. $\endgroup$
    – nzaman
    Feb 24 '17 at 6:42
  • $\begingroup$ Not pretty much the whole thing was in the "cool weapon names" shelf in my knowledge box, nothing else. $\endgroup$
    – Mephistopheles
    Feb 24 '17 at 15:12
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Let me rephrase your question: if I know my enemy has a flamethrower, should I keep wearing straw suits? Now back to your question. These are the flaws I spot.

First flaw: you don't want to bring strong magnetic fields on a battlefield, for the simple reason they are like wearing a light turret on your head while crossing a dark field: it attracts everyone's attention on you, making you easily detectable. Even without fictional plasma cannons, there are real mines which are activated by magnetic fields, enough of a reason to remove all the magnetic field one can remove.

Second flaw: quickly changing a magnetic field alway come with a related induced current (blame Maxwell and his equations...). It's going to be a really (electro)cute weapon!

Third flaw: if the target is locked to you, you are locked to him. He can back fire simply on detecting a "locking", while you are still setting up the discharge.

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A short list of problems

  • If your personal hand-held plasma cannon is generating such a powerful magnetic field, powerful enough to attract other 'challengers', how are you going to hold on to it? Let me ask it to you this way, if this thing is exerting enough force on another person to pull them towards it, then you have to be basically playing tug of war with that person through your weapon. If you are playing tug of war with your weapon, how do you intend to use it. Honestly, you might as well lasso your enemies at that point. Plasma lasso? Didn't the Balrog use one in Lord of the Rings?

  • Plasma is hot. Even if you can theoretically contain the plasma itself, it is going to radiate heat away at a very high rate. A magnetic field will do nothing to keep IR radiation in. Air will not absorb or reflect this heat, and in fact it will help to actively convect it away, so there will be no radiant heat going back into the plasma stream. In any case, your plasma stream will lose heat rapidly, making it more like a flamethrower than a 'cannon.'

  • Given the above point, it is useful to look at a picture of a flamethrower in action.

enter image description here

Notice how far from the operator the flame starts. And that's for a flame that isn't even that hot, at least not compared to plasma. A plasma cannon will generate an intense burst of heat that is maximized at the point of emission. How are you going to protect the operator from that?

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  • $\begingroup$ answer to the points from top to bottom: 1.It's a more than 1000 degree extendable plasma knife in function. 2.the user is far away from it, or the system uses laughably small amounts of plasma. $\endgroup$
    – Mephistopheles
    Feb 23 '17 at 19:28
  • $\begingroup$ @RedactedRedacted I don't understand your statements. 1000 degrees is not a plasma, not for any material. If you use laughably small amounts of plasma then it will cool off laughably fast and be laughably effective. If you use a large amount of plasma, you will burn the operator by a large amount, unless somehow the enemy is closer to the weapon than the operator. $\endgroup$
    – kingledion
    Feb 23 '17 at 19:34
  • $\begingroup$ MethPat (pun intended) said, that sustaining the plasma requires way less energy than creating it, but we're talking about the king of critical research failures so I can't be sure. $\endgroup$
    – Mephistopheles
    Feb 23 '17 at 19:43
  • $\begingroup$ @RedactedRedacted The problem isn't generating the plasma, or keeping it hot, the problem is where the heat goes. $\endgroup$
    – kingledion
    Feb 23 '17 at 19:50
  • $\begingroup$ Into the target, some of it into the air some of it into the weapon, that keeps it from firing for prolonged periods of time. Besides, as a handheld weapon, it would require a power armor to wield a nerfed and restrained version of it, that still can overheat. $\endgroup$
    – Mephistopheles
    Feb 23 '17 at 19:54
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Another two problems that I can see:

1) plasma, being ionised gas, is not "flame". Its heat is dependent, in systems that we are able to create, on induced current, and its stability is dependent on magnetic containment in a vacuum. Thus, firing a stream of plasma into atmosphere, will just disperse the stream after short distance (short as in centimeters, not any real weaponisable range). To counter that, ideally, your weapon needs to create a containment of some sort, on the beam's way to the target. This is both technically hard (as you cant really project a magnetic bottle over large distances easily), and needs a huge energy budget.

2) plasma will not only emit thermal photons (i.e. heat), but it will also emit ionising radiation (Brehmsstrahlung / cyclotron radiation, X-rays, stray protons...). If you want the weapon operator, and anyone in his general area, not to get acute radiation injury, you will need quite heavy shielding to mitigate that (assuming you want high power levels in your weapon)

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