Electromagnetic propulsion is a type of electric propulsion in which propellant is heated to a plasma state and then accelerated.
Electromagnetic devices pass a large current through a small amount of gas to ionize the propellant. The ionized propellant ( plasma) is accelerated by an electromagnetic force called the Lorentz force,
B = magnetic field
Variable specific impulse magnetoplasma rockets or VASIMR
Variable Specific Impulse Magneto- plasma rockets is a spacecraft propulsion technique which is being developed. The techniques which are being used today are either high thrust and low specific impulse or low thrust and high specific impulse systems. The VASIMR bridges the gap between these two types of techniques available by being capable of switching to any one mode when need arises.