"There are two practical ways to create the magic conditions that make fusion happen. One is called magnetic confinement fusion and the other is inertial confinement fusion. There’s gravity too, of course, but for that you need scales bigger than can be created on Earth: you need, quite literally, a star. The magnetic approach is to bind the hot matter in a reactor with an invisible web of magnetic fields. The inertial approach sets matter crashing into itself, thereby both heating and compressing it, and aims to get all the fusion done before the assembled star matter falls apart again. NIF {the National Ignition Facility} uses lasers to do this."