360: The U.S. has invested billions of dollars trying to create a controlled form of nuclear fusion that could be the energy source for an endless supply of electricity. But as a federal laboratory prepares for a key test of the latest technology, even the project’s most enthusiastic supporters concede an actual pilot fusion plant is at least a decade away. In the rolling brown hills of Livermore, Calif., looms a 10-story building the size of three football fields stuffed to the rafters …