[InsaneRussian]

Well if you think of plasma weapons and the core idea, if the core would regenerate the plasma from somewhere that would be odd, cause the only thing that sorounds you is air and dirt in the air, no plasma there lol ^^
You could simply just have "Cores" for plasma in your bag or where-ever and when one is empty you just simply replace it with another one. First you start out with really small cores and crappy weapons but when you advance you get better and better weapons and cores etc etc :P