It’s not every day that you get to witness a genuine scientific breakthrough, but on Tuesday that’s exactly what the scientists at Lawrence Livermore National Laboratory had to share with the world with their announcement that they had ignited a fusion reaction that produced more energy than it took to create. This milestone, decades in the making, brings us one step closer to harnessing a potentially limitless source of clean energy. So on this edition of KCBS In Depth, we’ll hear from one of the scientists who helped get us here about how he and his colleagues managed to pull it off.  Guests:  Arthur Pak, among the scientists involved in the ignition experiment  Umair Irfan, correspondent, Vox Host: Keith Menconi