The Fusion Quest

Nuclear fusion offers the prospect of abundant energy supplies without the radiation hazards and toxic waste associated with nuclear fission. It has been known for more than sixty years that fusion is the source of energy in the stars. Research on fusion as a practical energy source began in 1958 when much secret work on the subject was declassified. T. Kenneth Fowler joined the Oak Ridge Laboratory as a new graduate in 1957 and has been involved in fusion research ever since. He was head of magnetic fusion research at Oak Ridge from 1970 and became professor in the University of California at Berkeley in 1988. He explicitly denies setting out to advocate fusion with this book, but he clearly believes in it as a future energy source. He recognizes, however, that there is much work still to be done and tells the story of fusion research with controlled enthusiasm.

In nuclear fusion two light nuclei are fused together to produce one heavier nucleus, and there is a slight loss of total mass which appears as energy. Numerous combinations of materials are possible, but in most experiments deuterium and tritium nuclei have been fused to form a helium nucleus. Deuterium is an isotope of hydrogen having a neutron as well as a proton in the nucleus, and in naturally occurring hydrogen about one atom in five thousand is deuterium. Tritium has two neutrons, and isotopes of lithium and boron are also candidates for fusion reactions. Because nuclei carry a positive electric charge they naturally repel each other, and for fusion to take place sufficient force must be applied to overcome this mutual repulsion.

The energy of the hydrogen bomb comes from nuclear fusion, and the initial force to bring nuclei together is provided by an atomic (fission) bomb. The aim of the “fusion quest” is to achieve fusion in a controlled manner so that the energy released can be used in a controlled manner. Fusion takes place in a plasma of ionized gas at very high temperatures, typically one hundred million degrees Celsius. The major problem in fusion research is containment: the plasma has to be contained but cannot be allowed to touch the walls of the containing vessel. Most research to date has used magnetic containment. Since the plasma is electrically conducting and carries a large electric current, it is magnetic. Most researchers have used strong magnetic fields to contain the plasma in a toroidal arrangement. Producing the magnetic field requires very high energy, and much effort has gone into the manufacture of superconducting magnets for the purpose. Research has been international, with cooperation among workers in America, Europe, Japan, and Russia. Fowler records that the first successful demonstration of controlled fusion occurred in the Joint European Torus (JET) in England in 1991. This was followed by a series of American experiments at Princeton, beginning in December 1993.

A different approach to the containment problem is to use inertial containment. The reaction takes place in a tiny pellet of material, which is projected into the reaction zone and heated by an array of very high power lasers. The intense heating at the surface also compresses the centre of the pellet, and inertia prevents the pellet from moving far in the tiny fraction of a second before fusion takes place. Another pellet is then moved in to continue the process.

This book is to be commended to all those readers of Technology and Culture who are not nuclear physicists. It is not a textbook, and it does not assume much scientific knowledge. All mathematics, except Einstein’s equation E=mc², is relegated to an appendix. The main text reads as though the author is chatting to friends about the matters that have filled his working life. He guides them round the apparatus with which he has worked, and discusses the things he has found especially interesting. The reader will not become an expert on nuclear fusion, but he or she will gain a broad understanding of...