They kind of work, longest fusion reaction is 70 seconds. The two main issues are:
* Keeping the reaction going indefinitely in a controlled way
* Doing so without the system power input being greater than the power output
* Keeping the reaction going indefinitely in a controlled way
* Doing so without the system power input being greater than the power output
They don't work as in produce power.
Teenagers build "working" fusion reactors.
No one has built a fusion reactor that produces useful power.