Magnetohydrodynamic drive

A magnetohydrodynamic drive or MHD propulsor is a method for propelling vessels using only electric and magnetic fields with no moving parts, using magnetohydrodynamics.

The working principle involves electrification of the propellant (gas or water) which can then be directed by a magnetic field, pushing the vehicle in the opposite direction. Although some working prototypes exist, MHD drives remain impractical.

Principle

Ship propulsion

An electric current is passed through seawater in the presence of an intense magnetic field, which interacts with the magnetic field of the current through the water. Functionally, the seawater is then the moving, conductive part of an electric motor. Pushing the water out the back accelerates the vehicle in the forward direction.

The physics equation describing this propelling force is F_mag = I (L × B) where L is the vector in the direction of the current 'I' and its length is the distance the current travels, B is the magnetic field, and × denotes the cross product.