2. Fusion Concepts

Early efforts to produce and control fusion reactions were based on then well-known principles of electromagnetic theory. A current passing through a gas was known to strip electrons from the gas atoms (ionization), to raise its temperature, and to produce a magnetic field surrounding the current. Raising the current increased the degree of ionization, the temperature, and the magnetic field strength. The magnetic field exerts a confining force on the column of ionized gas (dubbed “plasma” in a 1928 paper by Irving Langmuir), and as the current and magnetic field were raised, the column of plasma is compressed, raising its density and further raising its temperature. This was known as the “pinch effect” and was the basis of most of the early attempts to produce fusion conditions in the laboratory. The “pinch effect” had been predicted in 1934 by W. H. Bennett and, independently, in 1937 by Lewi Tonks, but little subsequent effort was devoted to pinch plasma properties in the 1930s. Later, pinch devices were fashioned into what came to be called “magnetic bottles” for the plasma. In the 1950s, some of these “magnetic pinch” devices studied for fusion were linear in geometry, and some were donut-shaped (toroidal). They went by a variety of sometimes-colorful names: Perhapsatron and Columbus at Los Alamos and Zeta in the UK [2].