Commonwealth Fusion Systems has raised $863 million in a Series B2 round backed by Google, Nvidia and Bill Gates, bolstering the MIT-spawned company’s bid to commercialize fusion energy. The proceeds will fund completion of a demonstration reactor under construction in Devens, Massachusetts. The device, now about 65 percent finished, aims to show for the first time that fusion can continuously generate more energy than it consumes and could be switched on within two years. Success in Devens would pave the way for a 400-megawatt commercial plant the company plans to build in Virginia by the mid-2030s, enough to power roughly 150,000 homes. Commonwealth Fusion previously raised $1.8 billion in 2021 and says it will pursue additional financing to deliver the larger facility.