The particles in a fusion reactor are moving at 10 km/s. They don't particularly care about gravity. For components of the reactor, gravity tends to be helpfu

The particles in a fusion reactor are moving at 10 km/s. They don't particularly care about gravity. For components of the reactor, gravity tends to be helpful. It's much harder to cool superconductors or generate steam if your liquids aren't flowing along the bottom. Turbines don't work nearly as well if their inlets are sputtering like a coffeemaker.