In Solis People of the Sun I call the M-Drive a Super VASIMR connected with a Clarke type inertial suppressor. I call jump a wormhole, and have mused on saying jump fuel is metastable exotic matter, negative mass protium used to tunnel through. Really a quick hand wave and done, I loathe changing rules if I don't have to, changing the explanations is fine though.
https://en.wikipedia.org/wiki/Variable_ ... sma_Rocket
https://en.wikipedia.org/wiki/Wormhole
https://en.wikipedia.org/wiki/Metastability
https://en.wikipedia.org/wiki/Negative_mass