How can 10^45 Joules of energy be generated?

I'm looking for the most practical method you can think of. This amount basically translates into converting the entire m of Jupiter into energy via E=mc^2. They say that a fusion reactor can put out 100 times more energy than what is put in. Could this process be repeated over and over until you've reached the desired energy level? I.e every time you fire up the reactor you get out x amount of energy and then you put it back into the system the next go around and get 100x back out over and over...