system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What are the current Problems with nuclear Fusion?

I remember some years back they had already 10 - 20 seconds stable nuclear fusion in one test reactor, but why is my Power still from some wind turbine and solar panels? (Question is about the Physical obstacles of the recent research, not about politics or economics)
gpt
You are creating something as hot as a star. No physical material we have is strong enough to withstand that kind of heat and pressure. Any metals, ceramics, even carbon nanotubes would melt and rupture instantly. 

So the reaction is contained by floating it inside of a magnetic field so it doesn't actually touch anything. This field has to be very strong to contain the energy being created, and so it takes a lot of energy to keep the field up. Currently we can create fusion reactions, but we always end up putting more energy into them than we get out of them. 

We either need to find a way to generate more energy in the reaction without needing additional energy to contain it, or we need to increase the efficiency of the magnetic torus that contains the reaction so it doesn't take so much energy to maintain. 

This is why cold fusion is so sought after, because without all of the heat then you don't need high energy toruses to contain the reaction.