It’s pretty much just that. If one designed a weapon that draws plasma from a fusion reactor using high powered electromagnets (that’s the easy part) how would it concentrate that beam and prevent it from dispersing once it left the barrel?

Would a weapon like this be capable of earth-to-orbit defense?

If you could think of any way of creating high energy plasma from a reaction that could be contained in something like an artillery shell that would be great.

P.S. The technology does not need to be achievable within the next 300 years.

  • 1
    $\begingroup$ It's worth noting that since plasma is like gas except more active, describing it as a "beam" is kind of like describing the output of a leafblower as a "beam" of air. It's a stream, and not inclined to collimation. $\endgroup$
    – jdunlop
    Oct 28, 2021 at 0:48
  • $\begingroup$ I did something a little like this in a story, but because I had alien experiencer mythology in the story, I used a hostile sentient plasma that WANTED to stay coherent and kill something. It was more fun. $\endgroup$
    – DWKraus
    Oct 28, 2021 at 1:15
  • $\begingroup$ You might want to look at this partly related question. worldbuilding.stackexchange.com/questions/3348/… $\endgroup$
    – DWKraus
    Oct 28, 2021 at 1:18

3 Answers 3


how would it concentrate that beam and prevent it from dispersing once it left the barrel?

It wouldn't. Plasma is extremely slippery stuff, and tends to be very hot (to stop it recombining into boring old gas) and in order to be an effective weapon it also has to be very dense. The technical name for a blob of very hot, very dense matter released into the wild is an explosion.

The trick, therefore, is to throw your explosion hard enough and fast enough that it hasn't expanded and cooled into harmlessness by the time it reaches your enemy. The example I usually give is perhaps a little outdated these days, but should give you some idea of what a proper plasma gun might look like: MARAUDER. The intent there was to flick a plasmoid at a few percent of the speed of light, so that it might travel a few thousand kilometres and hit a target.

No confinement is really practical.

A related weapon is perhaps the (in)famous Casaba Howitzer, a nuclear shaped charge that grew out of the Project Orion nuclear pulse propulsion project. With a bit of clever engineering, you can get quite a lot of the oomph of a nuclear explosion to go in one direction, more or less. Quite a lot still goes out in other directions, so it is quite a hazardous thing to be anywhere near when it goes off. The effect will be to generate a cone of very fast, reasonably dense plasma that might be able to seriously damage targets quite some distance away.

And would a weapon like this be capable of earth-to-orbit defense?

The problem with operating a weapon that fires out matter in an atmosphere is that it has to bash through a minimum of ten tonnes of atmosphere in order to reach space. All of your potential targets now effectively have a huge amount of armour which you have to punch through, requiring an enormous amount of overkill at ground level in order to provide useful amounts of damage at the top of the atmosphere.

That's very wasteful, and potentially makes even firing the weapon quite dangerous for the landscape around it.

The Casaba Howitzer mentioned above would seem unlikely to help here, given how small a nuclear fireball usually is in comparison to the thickness of the atmosphere, and the obvious issues of detonating very large actual nuclear weapons inside the biosphere in which you live.

And if you could think of any way of creating high energy plasma from a reaction that could be contained in something like an artillery shell that would be great.

I have good news for you! The real world has had nuclear artillery since the 50s.

Upshot-Knothole test of a 280mm cannon firing nuclear shells

This removes most of the problems with trying to pin down plasma, especially very very hot, very dense plasma that will be radiating away a lot of energy because you're dealing with readily storable precursor materials which are compact, stable and have a decent shelf life.

This technique also readily lends itself to being fitting to rockets and fired into space, ensuring that all the plasma is delivered to where it needs to go instead of wasting most of it on the way up.

  • $\begingroup$ Of course, at that point, what you have is an ICBM, not a "cannon". :D $\endgroup$
    – jdunlop
    Oct 28, 2021 at 17:57

/And if you could think of any way of creating high energy plasma from a reaction that could be contained in something like an artillery shell that would be great./

New Clear Furball

Piecing together a nuclear fireball

The tremendous energy generated by a nuclear explosion instantly vaporizes any nearby materials. On an atomic level, electrons are stripped away from gaseous atoms to form a plasma—a mix of ions from different elements and free electrons. As it rapidly expands, the plasma quickly cools back into gases, liquids, and finally solids.

You could have an artillery shell with a tactical nuclear weapon in it. It produces a nuclear reaction that produces plasma. We got those. Not me personally, dang those laws but we as in the people who have nuclear weapons on my behalf I hope. You can have several in your fiction.

The prospects of blowing a hot stream of plasma from orbit down to earth seems less likely. Plasma from a fusion reactor is not going to be very dense and it is going to be very frisky. Wayward ions will want to explore. There is a lot of stodgy cold gas it needs to get past on the way down that will dampen the ardor of that hot plasma.

Maybe you could use a vortex cannon.


The smoke ring produced is in fact a circulating donut-shaped mass of air and smoke which is technically referred to as a toroidal vortex. An illustration of such a vortex is shown below.

enter image description here

The toroidal cloud of plasma, I here assert, will stay coherent all the way through the atmosphere. Then the hot hotness of plasma will burn things up!
But I think once you say PLASMA VORTEX you can jump ahead to the next awesome thing.

  • $\begingroup$ Well, Three's gun 'Bubba' in Dark Matter suddenly makes a lot more sense. $\endgroup$
    – Corey
    Oct 27, 2021 at 23:46
  • $\begingroup$ Plasma vortex - have been tried, we don't know the outcomes. $\endgroup$ Oct 28, 2021 at 0:39
  • $\begingroup$ @AdrianColomitchi - I did all my best work in the early 90s $\endgroup$
    – Willk
    Oct 28, 2021 at 0:43
  • $\begingroup$ And you don't remember the spheromak? $\endgroup$ Oct 28, 2021 at 0:51

This question has no science related tags, but I wonder if it can ever work with plasma, when the device is on a planet with an atmosphere.. there are handier alternatives.

Shooting plasma into space ?

Plasma does not come in artillery shells. In the atmosphere - lightning - plasma is ionization of gases, caused by electric discharge. This cannot be controlled like a light beam or radiation, or field. It will be difficult to focus any "beam" through the atmosphere, to target something in space. I also wonder if plasma beam can propagate through near vacuum. There are no gas molecules to ionize.

enter image description here

Focusing the beam

Suppose you have a solution involving a beam that propagates in a straight line, there is a focus needed, else the beam (launched off the planet) would cause side effects or require zillions of watts. Actually I doubt if something in space will ever be "beamed" effectively, keeping direction and focus in air.

300 years

For this particular purpose, space base defense, röntgen-laser, and visible light laser have already been investigated. A gamma laser may work, we may have that in 300 years. The energy of your portable fusion module is converted into gamma radiation and focused.

Self-guiding AI ballistics - missiles - are developed now and may become available for space war purposes. Autonomous robotic sats firing them may be easier and cheaper than using earth-based bases requiring high energy.

In 300 years, when there is any reason to put up a planetary defense to protect us from alien invasion, there will be space stations.. large space stations, fully automatic, with several weapon systems mounted on it. Your fusion reactor could be in orbit, armed with heavy lasers.


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