I recall the initial energy for heating to plasma is from electrical current. These "I Squared R losses" are I^2 X R where I is current and R is resistance.
Oh right, thanks mate. Does the magnetic field push the atoms together?
The magnetic fields hold the particles in the plasma together. The heat is applied through either an induced current or something like a laser or other EM radiation I believe. They turn on the electromagnets, introduce the gas, and then ionize and use the magnetic field to hold it together. (They might ionize it first however, I'm not sure.) Applying further heat gives the plasma enough energy to fuse.