Mirror Fusion Test Facility

The mirror fusion test facility during construction, part of the Yin-Yang magnets can be observed in the background.

The Mirror Fusion Test Facility, or MFTF, was an experimental magnetic confinement fusion device built using the magnetic mirror, or so-called "yin-yang" design. It was designed and built at the Lawrence Livermore National Laboratory (LLNL), one of the primary research centers for mirror fusion devices. It cost 372 million dollars to construct, making it at the time, the most expensive project in the lab's history. It opened on February 21, 1986 and was promptly shut down. The reason given was to balance the United States federal budget.^[1]

Following on from the earlier Baseball II device, the facility was originally a similar system in which the confinement area was located between two horseshoe-shaped "mirrors". During construction, however, the success of the Tandem Mirror Experiment ("TMX") led to a redesign to insert a solenoid area between two such magnets, dramatically improving confinement time from a few milliseconds to over one second.^[2] Most of the fusion power would be produced in the long solenoid, the yin-yang magnets serving only to dam up the ends in order to maintain good plasma confinement in the solenoid. Limited to break-even energy balance, the magnetic mirror endcaps actually consume power, but much less than that produced in a solenoid of sufficient length. The new version, officially MFTF-B, started construction in 1977 and was completed in 1986, on the very day the project was canceled by the Reagan administration Department of Energy. No experiments were performed. Rollbacks in fusion research funding dramatically reduced funding levels across the entire field.

Parts of the MFTF have since been re-used on newer fusion experiments, one such re-use winning a recycling award.^[3]

References