sciencehabit writes: ITER, the international fusion experiment under construction in Cadarache, France, aims to prove that nuclear fusion is a viable power source by creating a "burning plasma" that produces more energy than the machine itself consumes. Although that goal is at least 20 years away, ITER is already burning through money at a prodigious pace. The United States is only a minor partner in the project, which began construction in 2008. But the U.S. contribution to ITER will total $3.9 billion—roughly four times as much as originally estimated—according to a new cost estimate released yesterday. That is about $1.4 billion higher than a 2011 cost estimate, and the numbers are likely to intensify doubts among some members of Congress about continuing the U.S. involvement in the project.