Not sure what you mean by "engine" in this sense. Nuclear energy is released in an apparatus called a "reactor."
As fusion reactors are still theoretical and have not been realized on a practical level, the effort is currently considered pure research. The people working on it are research physicists, though some of them have degrees in nuclear physics, and could easily be called nuclear physicists.
To get an idea of who these people are, run an internet search on "nuclear fusion."
EDIT: Yes, Little Genie, Yahoo!News is lying to you. Not intentionally, perhaps, but the world is full of confusion and misinformation about modern physics in general and the Nuclear Fusion concept in general. The web sites you list say the same thing I am saying; you just need to read more carefully.
For the best quality information, talk to a physics teacher or visit the library and ask the librarian for help finding out about the real story on nuclear fusion.
And yes, the machines are still theoretical. When it is first done on a practical level, it will be one of the biggest news stories in history, and you won't be able to miss it. It will put the oil companies out of business, and we will hear about that.
The reason the answer seems indefinite is that I am right and the others are wrong.