[moffkalast]

Don't ionic thrusters typically solve this problem by also emitting oppositely charged particles from a thin rod behind the motor? Maybe that still causes drag, but overall the main problem is that while the ISP is high, the thrust is almost non-existent.

[ben_w]

They do indeed; the oppositely charged particles being electrons. But there's no charged particles lighter than an electron, and the only one with the same mass is the positron. If you try to balance it with protons, then what you've really got is a slightly over-complicated hydrogen-based ion drive.