From: Rowan Hamilton <rowanham@gmail.com> - When I was just a boy, I used to be a plasma physicist working on fusion research. I worked on a tokamak at UT and later on a multiple mirror plasma device at Berkeley. There are many issues to be resolved in this field. Tokamaks resolve one by getting rid of magneto-hydro-dynamic instabilities induced by the cylindrical symmetries of solenoidal devices. The actual extraction of usable energy is another issue that may not have been resolved. (I left this field a long time ago.) But I know that the break even point of a tokamak fusion reactor generating enough (unextracted) energy to sustain the reaction was reached way back in the 1980's at Princeton's TFTR.
--actually, break-even has never been achieved anywhere, though some lies have been told to try to get funding from gullible governments. Indeed TFTR did tell that lie, but their current web pages retract the lie, claim they never achieved break-even, and pretend they never told the lie in the first place. I speculate this was probably because the ITER project put pressure on them to stop lying, because ITER's goal was to ultimately achieve break-even, and they did not find it convenient for that lie to persist, since then there was no reason for ITER to get funded. Even if TFTR had achieved breakeven, which they did not, it would be only in a totally useless sense having nothing whatever to do with actually-usefully-extractible energy. In any real sense they were off by an enormous factor from breakeven and so will ITER. TFTR incidentally after lying to the surrounding community saying no safety risk so just quit complaining and let them go ahead with a tritium run don't worry [this run was totally unnecessary from a science standpoint, but useful for a public relations fundraising standpoint -- it was utterly stupid since even a brief run with T made the whole enormous place too radioactive to go in for about 1 year and extrapolations from all-D to T runs were readily makable mathematically]... then managed to leak away their entire stock of tritium into the Princeton/Plainsboro area where I lived at the time. Then the claim to the community ("it is utterly impossible that we will leak") changed to "oh don't worry, that tritium's probably in the upper atmosphere by now" with zero supporting evidence given for that claim. Tritium is very hazardous. I've got a very low opinion of fusion research and researchers, in case you did not notice. They lie, they lie huge, they do it often, they endanger thousands cavalierly, their entire projects are utterly pointless in the sense that even success beyond their wildest dreams represents failure from an engineering/economic view, and they've had a many decade history of astonishing incompetence and overhypitude. Eric Lerner's company, in contrast, would if it succeeded, genuinely succeed, and do so at a cost far smaller than TFTR. I just do not believe they will succeed, and I also believe in the big bang contrary to Lerner's book "The big bang never happened."