Inside the Tandem Mirror Experiment (TMX)
1978. TMX was designed to test the stability of confining superhot fusion fuel in a new geometry. In the tandem mirror concept, magnetic mirrors are placed at either end of a central magnetic tube. Very hot and dense plasmas contained inside the mirrors enhance the confinement of another plasma inside the central tube, where the bulk of the fusion would occur.
More information at: The Technology of Mirror Machines -- LLL Facilities for Magnetic Mirror Fusion Experiments (1977)