toroid was a large iron core from a transformer, which was used to induce current into the gas. The Perhapsatron quickly displayed the same problems as the British experiments. No matter how slowly the current was added, once it reached a critical point the instabilities arose. In 1954, Martin David Kruskal and Martin Schwarzschild published a critical paper on the issue, which suggested that all Z-pinch devices were inherently unstable. Tuck proposed the addition of a second, steady, magnetic field running longitudinal along the tube, a concept he called "adding a backbone to the plasma". Several modifications to the Perhapsatron were made to test variations on these concepts, but none proved fruitful. Z-pinch goes out of favor The failure of Perhapsatron was followed by the failure of other pinch devices. Another team at Los Alamos had been working on another fast-pinch machine known as Columbus that used electrical fields instead of magnetic, producing the same results. Meanwhile the much larger ZETA machine in the UK also failed, after publishing results with great fanfare saying they had successfully achieved fusion. By 1961 work on Z-pinch devices had largely ended, although some research continued on the related theta-pinch concept. Tuck never restricted himself to the pinch concept, and he spent considerable effort on other concepts, which led to joking within Los Alamos about his apparently unfocused work. Over the years he led development of several other concepts, including the picket-fence reactor, new pinch concepts, and work on mainstream devices. References Bibliography Joan Lisa Bromberg, "Fusion: science, politics, and the invention of a new energy source", MIT Press, 1982 Robin Herman, "Fusion: the search for endless energy", Cambridge University Press, 1990 James Phillips, "Magnetic Fusion", Los Alamos Science, Winter/Spring 1983 Magnetic confinement fusion devices