There are three basic cells in the VASIMR engine.
A neutral propellant gas is injected into this chamber. It is then ionized and plasma is created.
In this cell, this electrically charged gas is heated to create a desired density. This is done using electromagnetic energy.
A magnetic nozzle is used to convert the energy of the plasma into velocity of the exhaust gases. In the second stage, the plasma detaches from the magnetic field and is exhausted to provide modulated thrust.
The magnetic field that is used to expel the plasma also protects the spacecraft because it keeps the plasma from touching the shell of the spacecraft. Plasma would likely destroy any material it came in contact with. The temperature of the plasma exiting the nozzle is as hot as 180 million degrees Fahrenheit (100 million degrees Celsius). That's 25,000 times hotter than gases expelled from the space shuttle.