An advanced magnetic mirror that uses end-cell plasmas to create electrostatic plugs — trapping ions in a long central cell to achieve reactor-relevant confinement in a linear geometry.
ReviewedLast reviewed: 9 Aug 2026·Category: Concepts & Physics
Concept
A tandem mirror consists of a long, cylindrical central cell bounded by two end cells (plugs). The end cells contain higher-density, higher-temperature plasma that creates a positive electrostatic potential peak relative to the central cell. This potential barrier confines ions in the central cell, while electrons are confined by the ambipolar electric field. The result is a linear plasma column with confinement limited by radial transport rather than end losses.[1]
Thermal barrier: The key advance in tandem mirror physics was the thermal barrier concept (Baldwin and Logan, 1979), which creates a potential depression between the plug and the central cell. This allows the plug electrons to be hotter than the central cell electrons, reducing the power required to maintain the confining potential. The thermal barrier transformed the tandem mirror from a curiosity into a viable reactor concept.
Experiments
Major tandem mirror experiments included TMX and TMX-U (LLNL, 1979–1987), GAMMA 10 (University of Tsukuba, 1983–present, now GAMMA 10/PDX), and TARA (MIT, 1984–1989). TMX-U demonstrated the thermal barrier concept. GAMMA 10 achieved record ion temperatures for mirrors and continues to study plasma-wall interaction physics.[2]
Modern Relevance
The tandem mirror concept is being revisited with modern high-temperature superconducting magnets, advanced neutral beams, and improved plasma heating. Kronos Fusion Energy’s Aegis and MetroVolt burner products are based on a D–3He tandem mirror design. Realta Fusion is developing a compact tandem mirror for near-term applications.[3]
Sources
Baldwin, D.E. and Logan, B.G. "Improved tandem mirror fusion reactor." Physical Review Letters, 43, 1318, 1979.
Simonen, T.C. "Experimental progress in magnetic-mirror fusion research." Proceedings of the IEEE, 69, 935, 1981.
Post, R.F. "Mirror systems: fuel cycles, loss reduction and energy recovery." BNES Nuclear Fusion Reactor Conference, 1969.