I have gotten my hands on a plasma gun. And have recently discovered the "joys" of nanoswarms attacking us.
Now I'm interested in taking the big flipping plasma gun, and making it more effective against nanoswarms.
Right now, the idea I've got is to step down the size of the bolt/blast/charge to much smaller, in order to make the heat less of an issue. The weapon will still do plenty of damage to nanomachines, since they're so small, but it'll be something you can spread out, and keep up a steady output of damage, rather than shooting twice every three actions.
My current idea is to step it down to assault rifle damage, with 0 AP, because each individual plasma burst is relatively tiny, but giving it the various fire modes, and doing full damage to nanoswarms. Rather than the normal 1d10 damage, it does 2d10 or whatever because it's making the cloud swiss cheesed with lots of holes all over the place, rather than one big hole through the center. The 0 AP and lack of different ammo (no AP, for example) would make it much less effective against more solid targets. Maybe even make it spend a round cooling off if it's used in full auto, to show that it's still not a perfect nanomachine killing plasma hose.
Other possibilities included some sort of shotgun blast, of wide area, less dense energy, but in terms of in game skills, that requires more than I'm really comfortable attempting, whereas you could get most of the way to the previous option with tweaking settings.
I ask you for other options to share with the GM, if there's other ways to do this, or something similar.