Congress is poised to pull the plug on the International Thermonuclear Experimental Reactor (Iter), a collaboration between the US, European Union, Russia and Japan to build a prototype machine for the generation of power by nuclear fusion.
It is trying to bar the US from agreeing a three-year extension to the engineering design phase of the project. Each of the other parties has signed up to the extension, although they were due to select a site and start building the machine this year.
Supporters of the project accuse Congress of an insular attitude and say its treatment of Iter has been inconsiderate. Yet its caution appears grounded. Many US fusion experts believe the construction of Iter is premature, and that more research should be done first to establish a more realistic basis for a commercial fusion reactor.
Iter would be a gargantuan enginee/ring effort, which would cost about $11bn to build. It will attempt to fuse immensely hot hydrogen plasma as it circulates in a vast, lifebelt-shaped container which constrains it by means of a magnetic field. If successful, the Iter design would keep the hydrogen in a state of ignition, where the energy created by fusion would more than match the energy injected into the system, and therefore sustain itself for up to 20 minutes.
But the experimental reactor falls far short of serving as a full prototype for a fusion power station. The reactor vessel walls, for example, would disintegrate under radiation damage if ignition was sustained for any period of time. And there is no realistic mechanism for cooling the device during sustained operation.
Congress is disturbed that European and Japanese Iter advocates express commitment to the machine, although their own governments are unprepared to support its multi-billion dollar construction. And since the technical bureaucracies of Europe and Japan have been reluctant to ask embarrassing questions about the expensive and futile pursuit of the wrong machine, it appears the US will get the blame for the collapse of the project.