Abstract: Martin Greenwald stands in a windowless control room at Massachusetts Institute of Technology, holding a heavy, thick cable in his left hand. Pinched between his right index finger and thumb is a thin strip of dull-brown metal tape. That strip can carry as much electrical current as the hefty cable, he explains, and could enable scientists to build a mighty machine they've been dreaming about for decades. By winding spool after spool of the yttrium barium copper oxide tape into some of the strongest magnets on Earth, scientists at the MIT Plasma Science & Fusion Center hope to build a nuclear fusion reactor. If all goes well, these ultrastrong magnets will lasso and wrangle a roughly 100 million ºC hydrogen plasma, driving its protons to fuse and releasing tremendous amounts of energy over sustainable time periods. Commonwealth Fusion Systems, a spin-off company from this MIT project, hopes to turn the