Plans began to build a much larger machine based on the same principles, the Mirror Fusion Test Facility (MFTF).

When a current ran through the windings, the resulting magnetic field would pinch down at the ends, causing the electrons and ions to reflect back into the center and thereby stay confined.

[3] The mystery was solved at an international meeting in 1961 when Lev Artsimovich asked if the Livermore teams had calibrated a particular measurement instrument to account for a delay in its readings.

There was already a significant amount of research on how to avoid this problem, and at the same 1961 meeting, Mikhail Ioffe presented data from one such design, the "minimum-B", which showed clear signals that it was suppressing this instability.

This design added additional current-carrying wires that modified the magnetic field to bend the plasma into a bow-tie shape instead of a simple cylinder.

Livermore's Ken Fowler took this basic design and modified it to produce the "yin-yang" variation, whose magnets were much closer to the plasma.

The fusion directorate, now under the direction of Robert L. Hirsch, began to redirect the labs away from pure research towards an effort to make a working reactor design.

Dean, visited LLNL and told them that to remain in the running, they would have to produce a design that was competitive with the tokamaks in the short term.

He found an ally in the lab's director, John Foster, Jr., who broadly agreed with Dean's assessment of the political situation.

The major change was the addition of more neutral beam injectors, from two to a total of twelve, which would greatly improve the density and temperature of the plasma.

2XIIB was constructed rapidly and began operations in 1975, quickly meeting the performance goals in terms of temperature and density it had set for itself.

[8] The success of 2XIIB allowed Dean to get permission in April 1976 to fund the construction of what was essentially an enlarged version of 2XIIB known as MX, setting the initial operational date in 1981.

While MX might match the plasma performance of the newer tokamaks, calculations showed that even in the absolute best case it would be limited to about Q = 1.2, where a commercially useful system would likely need to have 10 or more.

The two mirrors would still have relatively low Q on their own, but over time the hot plasma they naturally leaked would heat the fuel in the solenoid to the point where it was undergoing fusion as well.

By trapping a volume of ions in the mirrors, electrons would be attracted to the two sides of the reactor, forming an area of negative charge.

[11] With this advance suggesting the mirror was in the running for both breakeven and as a practical reactor, LLNL proposed building a smaller machine than MX to test the layout.

This, in turn, creates a net positive charge, providing additional forces that help push the fuel out of the mirror, increasing the rate of leakage.

In 1979, Fowler, David Baldwin and Grant Logan suggested a new layout for these injectors that appeared to be able to produce a "thermal barrier" that should greatly reduce the leakage.

To test barrier the concept, in 1979 Fowler proposed taking TXM offline once its current experimental runs had ended in 1981.

In late 1979, Fowler proposed continuing the construction of MTFT-B with allowances so that the injectors could be modified if need be based on the results from TMX-U.

[13] The TMX was formally proposed by Fred Coensgen and the Livermore team on January 12, 1977 to the US Energy Research and Development Administration.