Why are we operating on this premise? We don't need to operate outside the law of conservation of energy to produce this energy. It comes from mass. E = mc2.
If I remember correctly, the energy in a nuclear fusion reaction comes from the nuclear strong force finally overcoming the electroweak force. When it does, it releases energy. There are some matter anti-matter reactions included in this, but I'm pretty sure most of the energy comes from the energy released do to the formation of nuclear bonds.
Well, since we don't know the properties of the EM field we cannot say with certainty whether it will consume more energy. But to challenge your analogy, what I'm suggesting is more like the proposition of maintaining the movement rate of an electron within a volume surrounded by a negative electrical field in a vacuum. 
It only makes logical sense to conclude that it takes more energy. I do, however, agree that none of us know for sure. I don't think that such an intensely strong EM field could be produced without consuming massive amounts of energy. Also, how do you propose that spacial area contained inside of the EM field is a vacuum? If it's a vacuum, there's no potential for thermal energy and the entire experiment/idea is useless.
You'd have to concentrate the heat to a pretty confined area. That means they're going to have to find a way to provide a path for the heat to travel or break the entire barrier for fractions of a second.
Regardless of the progress made in these experiments, we're still a long way from using nuclear fusion as a power source.
Hah.. Forgetting the stages of matter? That stuff comes before it gets to a gas.
Matter behaves in unpredictable ways (to someone with only elementary knowledge, anyway) when its under extreme conditions. Look at the core of the Earth. It's solid.
