I said efficiently, you would be lucky to get 1% efficiency there. Vacuums don't conduct heat very well do they.
replyWhile true in isolation, that is the wrong reason to care.
replyWe get power from the sun very effectively over 150 billion meters of vacuum.
Biggest problem with fusion is doing the fusion for a low enough input power (or for pulsed, energy) cost.
Literally 100% of that heat travels from the 1000000C stuff to the environment throught that vacuum. Vacuum doesn't just remove energy.
replyIf you use a steam engines it doesn't matter if your source of heat is 900C or 1000000C, all heat will be captured, and 40-60% will be turned into electricity.