Mikhail Solomonovich Ioffe (Russian: Михаил Соломонович Иоффе; 2 September 1917 – 14 July 1996) was a Soviet physicist best known for his work on magnetic mirror fusion devices, and especially his 1961 experimental device that demonstrated gross plasma stability was possible in a properly arranged magnetic field.
[1] By adding additional magnets to the mirror, the internal fields were modified so that the plasma sat within an area that was convex everywhere.
Ioffe led the construction of a device to test this theory, adding six current conducting bars to a conventional mirror to modify the internal field.
This was something of a mystery until Lev Artsimovich asked a question about whether one of the key measurement devices had been calibrated to account for a well known delay in its output.
The mystery was solved; accounting for this delay demonstrated that the US mirrors were completely unstable as Ioffe's work suggested.