What’s more, if you try to invest the enormous energies required to keep the plasma hot despite the cooling effect of the container walls, then the walls will gradually heat and melt. Nor must one wait for the walls to melt and the plasma to escape before finding the attempt at fusion ruined. Even as the walls heat up they liberate some of their own atoms into the plasma and introduce impurities that will prevent the fusion reaction. Any material container is therefore out of the question. Fortunately, there is a nonmaterial way of confining plasma. Since plasma consists of a mixture of electrically charged particles, it can experience electromagnetic interactions. Instead of keeping the plasma in a material container, you can surround it by a magnetic field that is designed to keep it in place. Such a magnetic field is not affected by any heat, however great, and cannot be a source of material impurity. In 1934, the American physicist Willard Harrison Bennett (1903- ) had worked out a theory dealing with the behavior of magnetic fields enclosing plasma. It came to be called the “pinch effect” because the magnetic field pinched the gas together and held it in place. The first attempt to make use of the pinch effect for confining plasma, with eventual ignition of fusion in mind, was in 1951 by the English physicist Alan Alfred Ware (1924- ). Other physicists followed, not only in Great Britain, but in the United States and the Soviet Union as well. The first use of the pinch effect was to confine the plasma in a cylinder. This, however, could not be made to work. The situation was too unstable. The plasma was held momentarily, then writhed and broke up. [Illustration: _Plasma in a magnetic field._] [Illustration: _Enormous machines and complex equipment, such as the Scyllac machine shown above, are required for nuclear fusion research._] Attempts were made to remove the instability. The field was so designed as to be stronger at the ends of the cylinder than elsewhere. The particles in the plasma would stream toward one end or another and would then bounce back producing a so-called “magnetic mirror”. In 1951 the American physicist Lyman Spitzer, Jr. (1914- ) had worked out the theoretical benefits to be derived from a container twisted into a figure-eight shape. Eventually, such devices were built and called “stellarators” from the Latin word for “star”, because it was hoped that it would produce the conditions that would allow the sort of fusion reactions that went on in stars. All through the 1950s and 1960s, physicists have been slowly inching toward their goal, reaching higher and higher temperatures and holding them for longer and longer periods in denser and denser gases.