compared to the current best number on 2XII of 8x109. After considerable concern from the researchers that this would be impossible, Dean backed off to 1011 being demonstrated by the end of 1975. DCLC Although 2XII was nowhere near the level needed by Dean's demands, it was nevertheless extremely successful in demonstrating that the yin-yang arrangement was workable and suppressed the major instabilities seen in earlier mirrors. But as experiments continued through 1973, the results were not improving as expected. Plans emerged to brute-force the performance through the addition of neutral-beam injection to quickly raise the temperature in an effort to reach Dean's conditions. The result was 2XIIB, the B for "beams". While 2XIIB was being set up, in November 1974, Fowler received a letter from Ioffe containing a series of photographs of oscilloscope traces with no other explanation. Fowler realized they demonstrated that injecting warm plasma during the run improved confinement. This appeared to be due to a long-expected by so-far unseen instability known as "drift-cyclotron loss-cone", or DCLC. Ioffe's photographs demonstrated that DCLC was being seen in Soviet reactors and that warm plasma appeared to stabilize it. 2XIIB reactor started real experiments in 1975, and significant DCLC was immediately seen. Annoyingly, the effect grew stronger as they improved the operating conditions with better vacuum and cleaning of the interior. Fowler recognized the performance was identical to that of Ioffe's photographs, and 2XIIB was modified to inject warm plasma during the center of the run. When the results were seen, they were described as "sunlight was breaking through the clouds and there was the chance that everything would be all right." Q-enhancement and tandem mirrors In July 1975, the 2XIIB team presented their results for nT at 7x1010, an order of magnitude better than 2XII and close enough to Dean's requirements. By this time, the Princeton Large Torus had come online and was setting record after record, prompting Hirsch to begin planning for even larger machines for the early 1980s with the explicit goal of hitting breakeven, or Q=1. This became known as the Tokamak Fusion Test Reactor (TFTR), whose goal was to run on deuterium-tritium fuel and reach Q=1, while future machines would be Q>10. With the latest results on 2XIIB, it appeared that a larger yin-yang design would also improve performance. However, calculations showed it would only reach Q=0.03. Even the most developed versions of the basic