Machine creates plasma hotter than the Sun and solves one of fusion energy’s biggest problems. At the UK’s Culham Campus, scientists are running experiments inside a machine that heats plasma to over 54 million degrees Fahrenheit (30 million Celsius) — nearly twice as hot as the Sun’s core. It’s called MAST Upgrade — the world’s largest operational spherical tokamak. And right now, it's taking on one of fusion’s toughest challenges: how to handle the extreme heat pouring out of a fusion reactor.