What you need to know about the U.S. fusion energy breakthrough

Shannon Osaka in The Washington Post:

Existing nuclear power plants work through fission — splitting apart heavy atoms to create energy. In fission, a neutron collides with a heavy uranium atom, splitting it into lighter atoms and releasing a lot of heat and energy at the same time. Fusion, on the other hand, works in the opposite way — it involves smushing two atoms (often two hydrogen atoms) together to create a new element (often helium), in the same way that stars creates energy. In that process, the two hydrogen atoms lose a small amount of mass, which is converted to energy according to Einstein’s famous equation, E=mc². Because the speed of light is very, very fast — 300,000,000 meters per second — even a tiny amount of mass lost can result in a ton of energy.

What is “net energy gain,” and how did the researchers achieve it?

Up to this point, researchers have been able to fuse two hydrogen atoms together successfully, but it’s always taken more energy to do the reaction than they get back. Net energy gain — where they get more energy back than they put in to create the reaction — has been the elusive holy grail of fusion research. Now, researchers at the National Ignition Facility at the Lawrence Livermore National Laboratory in California are expected to announced that they have attained net energy gain by shooting lasers at hydrogen atoms. The 192 laser beams compress the hydrogen atoms down to about 100 times the density of lead and heat them to approximately 100 million degrees Celsius. The high density and temperature cause the atoms to merge into helium.

More here.