No energy technology is more tantalizing than fusion, but no energy technology has proved more disappointing. So how has a fusion company in Southern California raised nearly half a billion dollars from the likes of Goldman Sachs and Paul Allen? Does it actually see a way to build a reactor that could generate vast amounts of clean power, even while other fusion projects have perpetually remained 20 years away from reality? In search of the answers, I visited the headquarters of Tri Alpha Energy in the spring. The coastal fog was lifting from the rolling hills in Foothill Ranch as...