Many fusion reactors are based on a tokamak design, which uses an electrical current to twist a superheated plasma's electrons and ions into a three-dimensional loop. That's good for containing the plasma, but it's still not the safest design -- if the current fails or there's a magnetic disruption, you have a serious problem on your hands. However, scientists at the Max Planck Institute may have a more practical alternative. They've recently completed Wendelstein 7-X, the first large reactor based on a stellarator concept that relies on a cruller-like shape for the twisting action instead of a current. That's considerably safer than a tokamak, and the supercomputer-guided design should iron out the containment problems that have plagued stellarators until now.