[macilacilove]

Can somebody explain, what exactly is "ignition"? If even a single helium atom is fused you have "more energy than you have put into it". That does not seem impressive.

[dist-epoch]

No, you have more energy than two separate helium atoms.

You haven't counted the energy required to make them fuse in the first place.

[eesmith]

There is a nice Sankey diagram at https://en.wikipedia.org/wiki/National_Ignition_Facility#Sys... showing where the energy losses go.

[ynlefevre]

this may help: https://lasers.llnl.gov/science/ignition