I think "sustainably" is implied, and the author's next sentence makes that a bit clearer. > But through the use of promising fusion technologies such as magne

I think "sustainably" is implied, and the author's next sentence makes that a bit clearer. > But through the use of promising fusion technologies such as magnetic confinement and laser-based inertial confinement, humanity is moving much closer to getting around that problem and achieving that breakthrough moment when the amount of energy coming out of a fusion reactor will sustainably exceed the amount going in, producing net energy.