 The yin-yang magnets would then serve 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 consumed power, but much less than that produced in a solenoid of sufficient length.A new version, officially MFTF-B, started construction in 1977 and was completed in 1986 on the very day the project was canceled.