The U.S. Energy Department will announce Tuesday that government scientists at the Lawrence Livermore National Laboratory in California have for the first time produced a net energy gain in a fusion reaction, a major step toward limitless, inexpensive clean energy, the Financial Times and The Washington Post reported Sunday. Scientists have been trying since the 1950s to recreate the kind of fusion reaction that powers the sun, but none have been able to produce more energy than the process consumes.   Energy Secretary Jennifer Granholm is scheduled to unveil a "a major scientific breakthrough" at the Lawrence Livermore lab on Tuesday, though the Energy Department is tight-lipped about the nature of the announcement.  "Initial diagnostic data suggests another successful experiment at the National Ignition Facility," where the fusion research is talking place, the Lawrence Livermore National Laboratory told the Financial Times. "However, the exact yield is still being determined and we can't confirm that it is over the threshold at this time." A lab official told the Post that the results are still being analyzed and no findings will be released until Tuesday, though the Financial Times reports the fusion reaction produced about 120 percent of the energy it consumed. "The breakthrough was already being widely discussed by scientists," the Financial Times said, citing two people familiar with the findings who also said the greater-than-expected energy output had damaged some of the diagnostic equipment. The goal of fusion research is to harvest energy from colliding two atoms together at incredibly high speeds. The type of fusion studied at the Lawrence Livermore lab is called inertial confinement fusion, which involves hitting a tiny ball of hydrogen plasma with the world's biggest laser. Even if this experiment's success is confirmed, we're still years or decades from fusion power flowing through the energy grid, though "the technology's potential is hard to ignore," the Financial Times reports. "Fusion reactions emit no carbon, produce no long-lived radioactive waste, and a small cup of the hydrogen fuel could theoretically power a house for hundreds of years." It's the "holy grail" of clean energy, Rep. Don Beyer (D-Va.) said earlier this year at the launch of a new White House fusion power strategy. "Fusion has the potential to lift more citizens of the world out of poverty than anything since the invention of fire."