Magnetic Confinement The First Experiments

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 The First Experiments
As with most developments in science, many people were thinking along similar lines at the same time, so it is hard to give credit to any single person as the “discoverer” of magnetic-confinement fusion. There is some evidence of speculative discussions of the possibility of generating energy from
the fusion reactions before and during World War II. Certainly there had been discussions about the basic principles of fusion among the physicists building the atom bomb in Los Alamos. They had more urgent and pressing priorities at the time, and for various reasons they did not pursue their embryonic ideas on fusion immediately after the end of the war. However, many of these scientists
did return later to work on fusion.

 'FIGURE 5.1 George Thomson (on the left) and Peter Thonemann at a conference in 1972.
Thomson was awarded the Nobel Prize in Physics in 1937 for demonstrating the wave characteristics
of electrons'



The first tangible steps were taken in the UK. In 1946, George Thomson (Figure 5.1) and Moses Blackman at Imperial College in London registered a patent for a thermonuclear power plant. Their patent was quickly classified as secret, so the details were not made public at the time. In essence, the patent outlined a plan for hot plasma to be confined by a magnetic field in a doughnut- shaped vessel that superficially looks remarkably like present-day fusion
experiments. The proper geometric term for this doughnut shape—like an inflated automobile tire—is a torus. With the benefit of present knowledge of the subject, it is clear that this early idea would not have worked—but it displays remarkable insight for its day. The proposal provoked much discussion
and led to the start of experimental fusion research at Imperial College.

A parallel initiative had been started in 1946 in the Clarendon Laboratory at Oxford University. Peter Thonemann (Figure 5.1) had come to Oxford from Sydney University in Australia, where, earlier in the century, the so-called pinch effect had been discovered. The heavy electric current that had flowed through a hollow lightning conductor during a storm had been found to have permanently squashed it. If the pinch effect was strong enough to compress metal, perhaps it could confine plasma.

When an electric current flows through a conductor—in this case the plasma—it generates a magnetic field that encircles the direction of the current. If the current is sufficiently large, the magnetic force will be strong enough to constrict, or pinch, the plasma and pull it away from the walls. In a straight tube, the plasma will rapidly escape out of the open ends. However, if the tube is bent into a torus, it is possible in principle to create a self-constricted plasma isolated from contact with material surfaces.

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