Being accused of attempting the impossible is not unusual for the scientists and engineers working on nuclear fusion projects around the world. After all, they are attempting to capture, on Earth, the reaction that powers the Sun. Success could mean abundant, cheap and emission-free electricity. But the challenges are daunting. Fusion is the process of fusing hydrogen nuclei together, which releases immense amounts of energy. To maintain fusion here on Earth, extremely high temperatures - many times those found on the Sun - are needed. So, a fuel (usually a combination of the hydrogen isotopes tritium and deuterium) is heated until it becomes a burning hot plasma, which then has to be controlled and manipulated to spark fusion. There are a number of ways to do this, and Germany's Proxima Fusion is attempting one that is considered difficult, even by the extreme standards of the fusion industry. A common approach to fusion is to build a tokamak. It's a doughnut-shaped device, which uses powerful magnets to contain the plasma. But Munich-based Proxima is working on a stellarator. It also uses magnets to manipulate the plasma but the reaction container has a more complicated shape, with twists and turn. "There's real momentum across fusion right now," [said former nuclear submarine captain Ryan Ramsey]. "The real question now is not which concept is most interesting, but which can credibly deliver a power plant."