Editing Magnetic mirror (section)

===New geometries===
[[File:Baseball II magnetic mirror.jpg|thumb|right|The Baseball II was a superconducting version of the baseball coil design, seen here in 1969 during construction.]]
[[File:A picture of the 2XII Magnetic Bottle.jpg|thumbnail|The 1978 2X magnetic bottle experiment. Fred Coensgen is pictured. The cylinder holds one set of neutral beam injectors, the mirror itself is not visible.]]
The issue of the potential instabilities had been considered in the field for some time and a number of possible solutions had been introduced. These generally worked by changing the shape of the magnetic field so it was concave everywhere, the so-called "minimum-B" configuration.{{sfn|Bromberg|1982|p=111}}

At the same 1961 meeting, [[Mikhail Ioffe]] introduced data from a minimum-B experiment. His design used a series of six additional current-carrying bars in the interior of an otherwise typical mirror to bend the plasma into the shape of a twisted bow-tie to produce a minimum-B configuration. They demonstrated that this greatly improved the confinement times to the order of milliseconds. Today this arrangement is known as "Ioffe bars".{{sfn|Bromberg|1982|p=111}}

A group at the [[Culham Centre for Fusion Energy]] noted that Ioffe's arrangement could be improved by combining the original rings and the bars into a single new arrangement similar to the seam on a tennis ball. This concept was picked up in the US where it was renamed after the stitching on a baseball. These "baseball coils" had the great advantage that they left the internal volume of the reactor open, allowing easy access for diagnostic instruments. On the downside, the size of the magnet in comparison to the volume of plasma was inconvenient and required very powerful magnets. Post later introduced a further improvement, the "yin-yang coils", which used two C-shaped magnets to produce the same field configuration, but in a smaller volume.

In the US, major changes to the fusion program were underway. [[Robert L. Hirsch|Robert Hirsch]] and his assistant [[Stephen O. Dean]] were excited by the huge performance advance seen in the Soviet [[tokamak]]s, which suggested power production was now a real possibility. Hirsch began to change the program from one he derided as a series of uncoordinated science experiments into a planned effort to ultimately reach [[breakeven (fusion)|breakeven]]. As part of this change, he began to demand that the current systems demonstrate real progress or they would be cancelled. The [[bumpy torus]], [[levitron]] and [[Astron (fusion reactor)|Astron]] were all abandoned, not without a fight.{{sfn|Heppenheimer|1984|p=78}}

Dean met with Livermore's team and made it clear that Astron would likely be cut, and mirrors had to improve or face cutting as well, which would have left the lab with no major fusion projects. In December 1972, Dean met with the mirror team and made a series of demands; their systems would have to demonstrate an nT value of 10<sup>12</sup>, compared to the current best number on 2XII of 8x10<sup>9</sup>. After considerable concern from the researchers that this would be impossible, Dean backed off to 10<sup>11</sup> being demonstrated by the end of 1975.{{sfn|Heppenheimer|1984|p=78}}