Helion Energy, a startup developing engines powered by nuclear fusion, is certain to pique the interest of sci-fi fans. But the more important question for Helion President Philip Wallace is whether the same can be said of venture capitalists. That’s because the Seattle-based company is on the hunt for $20 million in financing to build a full-scale model of its fusion engine. That engine, which the company currently has a prototype of at one-third scale, works by forming hot, ionized hydrogen gas. The gas is then electromagnetically accelerated to greater than 1 million mph and collided in a burn chamber...