I thought that, but I now think it means in a single run, using just half a gram of hydrogen, the peak output power is 500MW, it would be helpful if it also mentioned how much usable energy was generated too.
I don't think anyone knows how much 'usable' energy ITER will generate (plus, ITER won't be a power plant -- the heat produced will actually be thrown away -- so I guess we won't ever know.)
ITER won't produce any stable power at all, so they most likely mean something like "A single run of ITER will consume about half a gram of hydrogen while having a peak output of 500MW (for a few seconds).
Yeah, the plan for ITER is to produce 500MW over 1,000 seconds, with an input power of 50MW (and 0.5 grams of deuterium-tritium fuel).
The current record is, like, 10 seconds and no one has broken even on input/output power...