There's a reason that plasma cannons are vehicle-mounted, they are massive: ChromSel, gold, osmium, iridium, platinum and rhuthenium are all major parts of the weapon.

Here, Borusa tried to carry the thing, but seems to have lost balance and is about to fall facefirst into what might as well be a big metal block; luckily the mechanism is pretty tough, so he doesn't have to worry about exploding.

The cannon functions by inserting a tiny bit of antiprotons into a water-oxonium mixture and channeling the explosion as a tight beam traveling close to c.