The Department of Energy plans to announce Tuesday that scientists have been able for the first time to produce a fusion reaction that creates a net energy gain — a major milestone in the decades-long, multibillion-dollar quest to develop a technology that provides unlimited, cheap, clean power.Huge amounts of public and private funds have been funneled into the fusion race worldwide, with the aim of ultimately manufacturing fusion machinery that could bring electricity to the grid with no carbon footprint, no radioactive waste and far fewer resources than it takes to harness solar and wind power.It was confirmed by two people familiar with the research, who spoke on the condition of anonymity to avoid getting ahead of the official announcement.Energy Secretary Jennifer Granholm was slated to make the announcement Tuesday at a media event billed as the unveiling of “a major scientific breakthrough.”The department and the lab declined to comment.Building devices that are large enough to create fusion power at scale, scientists say, would require materials that are extraordinarily difficult to produce."