Random thought: how would a nuclear/ion[vasimir type] hybrid work, and what performance could one get out of it in the long run?
[probably not worth the thought ex, but it was a horrible and bizarre mental image in a dream.]
That's not a bad thought. Under the right circumstances, such as a relatively high gravitational field and vacuum, as on the Moon, this might be the preferred engine.
Note that power is an external input. It's going to take a lot of power to operate the superconducting magnets, and to power the RF generators and antennae.
I'm thinking that this kind of device could lead to a truly multi-mode rocket engine, taking in atmospheric gases and heating them for rocket exhaust, then when transitioning to near space using the VASIMR system, and finally settling down to a low-thrust long-duration system for the long haul.