In the 1930’s scientists, particularly Hans Bethe, discovered that nuclear fusion was possible and that it was the energy source for the sun. Beginning in the 1940’s researchers began to look for ways to initiate and control fusion reactions to produce useful energy on earth. From the start, the task was difficult, because fusion reactions required temperatures of hundreds of millions of degrees, too hot to be contained by any solid chamber. Instead, physicists sought to contain the hot plasma with magnetic fields, using, for example, the pinch effect where electric currents moving in the same direction attract each other through their magnetic fields. This approach was called “magnetic confinement”.
Initially this work in the U.S., UK and USSR was secret. However, by the mid-1950’s administrators and scientists alike were convinced that controlled fusion research had no military applications, and in particular had nothing to do with the development of thermonuclear weapons. The first thermonuclear weapons had been detonated in the early 1950’s. In an H-bomb, or thermonuclear weapon, the tremendous energy of a fission-based nuclear weapon is used to heat up a large amount—tens or hundreds of kilograms—of a fusion fuel to release fusion energy in an explosion. By contrast, in controlled fusion research—and in a future fusion generator—not even one gram of fuel would be heated to high temperature at any one time. This tiny amount of highly heated fuel is far too small to serve as a “spark” for the kilograms of fuel needed for a weapon. In fact, any contact between the tiny amount of hot fuel plasma and a larger object, such as the fuel for a bomb, would immediately douse the fusion reaction by lowering the plasma’s temperature. (Thus the conversion of a fusion generator into bomb, sometimes portrayed in science fiction, is impossible.)
Since fusion research had no military applications, it was declassified by the major participating nations, and cooperation in fusion began between the U.S. and the USSR.
Starting in the 1960’s, after the invention of the laser, other researchers sought to heat fuels with a laser so suddenly that the plasma would not have time to escape before it was burned in the fusion reaction. It would be trapped by its own inertia. This newer approach was thus named ”inertial confinement”.
During this first period, scientists realized that the key problem for controlled fusion was the tendency of plasma to develop instabilities that led to plasma escape from the magnetic confinement. While most fusion approaches struggled to suppress these instabilities, which occur in all plasma, in 1964 U.S. and Soviet scientists simultaneously developed the plasma focus device, which sought to exploit the instabilities to compress energy, instead of trying to suppress them.
By the end of the 1960’s many different fusion devices existed and no one knew which approach would actually lead to practical fusion power. But in the mid-1970’s administrators in the United States decided to focus all magnetic confinement work on a single device, the tokamak, which had been invented in the Soviet Union. In part, this decision was due to the effort to portray fusion as a short-term solution to the oil crisis of the early 1970’s, requiring only engineering development. In fact, fusion was then, and still is, a research project, investigating which route to fusion power is best. The narrowing of funding to a single device was a major mistake. Read what the former director of the U.S. fusion energy program and an architect of the present Dept. Of Energy fusion energy program said about it in October 2017.
Another major error was in focusing nearly all research on deuterium-tritium fuel (DT). DT fuel undergoes fusion reactions at a lower temperature than any other fuel, but has serious drawbacks. It releases almost all its energy in the form of neutrons, which can only be turned into energy through the same expensive process of heating water to create steam, driving a turbine, that has been in use for over a century. In addition the neutrons produce radioactive waste in the reactor structure, and their damage forces DT generators to be large, to spread out the neutrons.
From the 1960’s, researchers knew that there were other reactions that avoided these drawbacks—called “aneutronic fusion” reactions, because they produced no neutrons or very few. The best of these fuels was hydrogen-boron or pB11 fuel, which produced no neutrons at all in the main reaction. (See aneutronic fusion.) These fuels needed higher temperature for fusion and research into them was barely funded, despite their great advantages for cheap, clean energy.
During the 1980’s and 90’s and in the past decade, several billions were spent on the tokamak, building larger and larger devices. Significant progress was made, but the plasmas remained far from stable. In the same period, despite the very small funding devoted to alternative approaches, researchers demonstrated that several devices including the plasma focus, initial electrostatic confinement and field reversed configuration could, in theory, achieve the high temperatures needed for aneutronic fusion. For the first two devices, such high temperatures were demonstrated experimentally. But progress remained slow due to a shortage of funds.