Magnetohydrodynamic drive
A magnetohydrodynamic drive or MHD accelerator is a method for propelling vehicles using only electric and magnetic fields with no moving parts, accelerating an electrically conductive propellant (liquid or gas) with magnetohydrodynamics. The fluid is directed to the rear and as a reaction, the vehicle accelerates forward.
Source: Wikipedia — Magnetohydrodynamic drive (CC BY-SA 4.0)