Wouldn’t a fusion reactor by necessity get as hot as the sun? It seems controlling the heat would be a non-trivial problem.
Current fusion reactors use temperatures much higher than the Sun’s temp.
Fusion on the Sun is possible because of an enormous pressure inside the Sun. There is no equivalent on Earth. Ever-higher plasma temperatures require more and more powerful magnets to keep the plasma levitating inside the reactor.
A large amount of input energy is needed to run the process, we are not close to have an energy positive sustainable fusion reactor.