WASHINGTON (AP) — Scientists announced Tuesday that they have for the first time produced more energy in a fusion reaction than was used to ignite it — a major breakthrough in the decades-long quest to harness the process that powers the sun.

Researchers at the Lawrence Livermore National Laboratory in California achieved the result last week, the Energy Department said. Known as a net energy gain, the goal has been elusive because fusion happens at such high temperatures and pressures that it is incredibly difficult to control.

The breakthrough will pave the way for advancements in national d...