Willard Harrison Bennett Biography (1903-1987)


Willard Bennett was an American physicist noted for his contributions to several areas of physics, including plasma physics, astrophysics, geophysics, surface physics, and physical chemistry.

Bennett was born in Ohio in 1903, and studied at the Carnegie Institute of Technology and the University of Wisconsin before receiving his Ph.D. from theUniversity of Michigan in 1928. He was elected to a National Research Fellowship in Physics, and in 1928-29 studied at the California Institute of Technology. In 1930 Bennett returned to his native state to join the Physics facultyat Ohio State University.

In the 1930s Bennett did pioneering research in plasma physics--the study ofgases ionized by high-frequency electricity. In 1934 he discovered the pincheffect, a electromagnetic phenomena that has important implications for plasmas at very high temperatures.

André Ampère demonstrated that parallel electric currents in awire having the same direction attract one another through the magnetic fields they generate. Imagining a current through a wire of a certain thickness asbeing composed of smaller individual components of that current all traveling within the wire, there will be a net inward pressure on the surface of thewire. This force is negligible at common current values, but can be quite significant for large values of the current.

The pinch effect, named by C. Hering in 1907, first showed up in early typesof induction furnaces in which large, low-frequency alternating currents of about 100,000 amps were induced. At high enough currents the metal ring-shapedconductors in the furnace could actually be closed off, or pinched, by the pressure. (Something similar has been seen to affect tube-shaped conductors inthe presence of a lightning strike.)

Bennett discovered the pinch effect in the context of plasma physics, where an extremely-high temperature plasma is confined to a region of space in an attempt to extract energy from a thermonuclear reaction in the plasma. For a plasma confined in the shape of a torus, and a transformer core passing throughthe axis of the torus, Bennett discovered the conditions for the pinch effect to occur, and derived a fundamental equation that described the current needed in order that a certain plasma temperature be reached. In this configuration, the current in the plasma has the double function of heating the plasmaand also compressing it toward the center of the torus tube. These studies and later research have been extensively used as scientists attempt to magnetically confine a plasma at temperatures high enough for controlled nuclear reactions to take place, such as at the Tokamak Fusion Test Reactor at PrincetonUniversity.

In 1936 Bennett proposed the tandem van de Graaff accelerator, which later became widely used in nuclear research. In 1950 he developed the radio frequency mass spectrometer, a nonmagnetic spectrometer that could determine the masses of atoms. Because it did not rely on a heavy magnet, it was the first launched into space, carried by Sputnik III. At the time it was the only space instrument used by the Russians that was credited to an American inventor in their own Russian-language publications. Also in the 1950s, Bennetts experimental tube called the Stormertron predicted and modeled the Van Allen radiationbelts surrounding the earth six years before they were discovered by satellite.

Bennett worked on aircraft equipment development as a U.S. Army officer during World War II, and from 1946-1950 served as chief of the physical electronics section of the National Bureau of Standards. He was a consultant for the U.S. Naval Research Laboratory, and went to North Carolina State University in1961, where he held the Burlington professorship. Bennett held 67 patents before his death in 1987. In 1991 he was inducted into the National Inventors Hall of Fame.

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