On some fictional science

When I look at my google drive something stands out to me: a folder called "Capital Ships". There's just something about this name that makes me envision huge behemoths duking it out. Not just ships, but the best ships of each fleet. The kind that cost dozens of times as much as most others. The kind that can singlehandedly decide how a battle between fleets turns out. It's not really hard for me to picture this kind of power.
Visions like this are, for me, glimpses to the past. I don't really have the kind of imagination that I did when I was small, so having some of it break through to me is unusual. I still think about science fiction in my own way, but nowadays it's more about the technologies involved and sometimes the kinds of creatures that might exist. My visions have become less mighty and more mundane.
However, through the mundane I have been able to understand my created world better. What are those huge balls of energy that I saw in Star Sonata? In that game they call them pulse guns. At one point I realized though, that my pulse guns are less like the orbs of shock from Star Sonata and more like balls of fiery plasma. Thus, I decided at one point that I should codify their technology.

The way my pulse guns work is that a ball of super-heated plasma is enclosed in a magnetic or gravitic field. This field is then propelled somehow toward the target. Some really advanced guns of this kind can also change their projectiles' direction while in flight.
What's notable about this technology is that while we are used to having fields remain around the machine that created them, these fields do not. Although they may be created the normal way, they actually use the extreme energy of plasma to keep themselves going. The mechanism for it is somewhat similar to how a balloon keeps shape when filled with water - it's the pressure of the water pushing outwards that keeps the water from dispersing. Plasma works the same way here.

Later on I realized that this technology could really be used for many things. Although hot plasma is not easy to come by, some versions of this technology don't need it.
A huge advantage of being able to control fields like this is that you don't need to propel matter in order to create thrust. Thus, the same technology can be used in a different way as engines for ships. With a relatively small device you can gravitize(as a parallel to magnetizing) entire ships. Energy cost is relative to mass of the ship, but that's not a fundamental problem, as that applies with most kinds of propulsion.
Due to not needing any reaction mass this propulsion method has huge efficiency gains over chemical thrusters. The efficiency gains mostly apply for longer-distance travel, but that isn't really rare in the days when humans know of hundreds of habitable planets.