They produced and ignition that could be self-sustaining. I suspect they had a mechanism to remove the fuel.
Actually, all of the fuel they could squeeze into the magnetic containment was already in place. There wasn't much of it. It takes either a great deal of gravity or a truly healthy magnetic field to do this. We don't manipulate gravity. It will take a big mass to make this hold together on its own, like for example, our sun. The energy required for the magnetic pinch plus the energy needed by the ignition laser was a great deal more than that two nano-second fusion produced.
Actually, out atmosphere will supply the fuel once they get it to self sustain.