Two ideas advanced in recent years for improving the confinement of plasmas in mirror machines have added much to the promise of such devices as potential fusion‐power reactors. In an experiment just completed at Livermore, the tandem‐mirror configuration, first suggested in 1976, appears to have passed its first major experimental test with colors flying.1The more recently proposed thermal‐barrier idea, which is expected to strengthen the confinement capabilities of the tandem configuration, will undergo its first experimental trial next year at this same, Tandem Mirror Experimental Facility (TMX).