A magnetic confinement approach that traps plasma between two high-field regions — one of the earliest fusion concepts, now experiencing a renaissance through private companies and modern superconducting magnets.
A magnetic mirror confines charged particles between two regions of strong magnetic field (mirror coils) connected by a weaker-field central region. As a particle moves toward a high-field region, the increasing field strength reflects it back toward the centre, creating a magnetic “bottle.” This effect arises from the conservation of the magnetic moment μ = mv⊥²/2B.[1]
Mirror machines were among the first magnetic fusion devices, pursued at Livermore and Oak Ridge in the 1950s–1960s. The simple mirror evolved into the tandem mirror (GAMMA 10, MFTF-B), which used end plugs to electrostatically confine ions and reduce end losses. However, large mirror machines proved difficult to stabilize against interchange instabilities.[2]
Several companies and research groups are revisiting the mirror concept using modern high-field superconducting magnets and improved plasma stabilization techniques. The Wisconsin HTS Axisymmetric Mirror (WHAM) experiment at the University of Wisconsin is testing a mirror configuration with a 17 T HTS magnet, and Reata Fusion is developing a commercial mirror reactor concept.[3]