What is nuclear fusion and what have scientists achieved?

After 70 years of research, experts in California have for the first time proven ignition is possible

In this 2012 image provided by Lawrence Livermore National Laboratory, a technician reviews an optic inside the preamplifier support structure at the Lawrence Livermore National Laboratory in Livermore, Calif. Officials at the Department of Energy say on Tuesday, Dec. 13, 2022, there will be an announcement of a “major scientific breakthrough” on nuclear fusion. (Damien Jemison/Lawrence Livermore National Laboratory via AP)

Physicists are a-buzz over new results from nuclear fusion experiments. 

But what have they found, and how big a breakthrough is it?