Negablaster actually sounds like a good name, but if it's still pending and you're open to suggestions... how about Psi-blaster or Psion Pulser or something like that.
It's supposed to be shortened for Negative Blaster. But I suppose there is the odd person who would think that, I guess I can consider giving it a different name as RPGFan suggested then.
I don't see a problem with NegaBlaster. You've explained what it stands for and it'll only be the odd person who construes it the wrong way. Even then, any publicity is good publicity.