(1901-1967) American Experimentalist, Particle Physicist
Robert Jemison Van de Graaff made a major contribution to advances in high-energy physics through his invention of what came to be called the Van de Graaff generator, an electrostatic high-voltage accelerator capable of accelerating electrons to millions of volts of kinetic energy.
He was born on December 20, 1901, in Tuscaloosa, Alabama, to Minnie Cherokee Hargrove and Adrian Sebastian Van de Graaff. His early education was in the public schools of Tuscaloosa. Intending to become a mechanical engineer, he studied at the University of Alabama, where he received his B.S. degree in 1922 and his M.S. the following year. He then took a job as a research assistant with the Alabama Power Company but left after only a year to travel to the Sorbonne in Paris to continue his education. The trip was to change the direction of his life. In Paris he attended the lectures of marie curie, one of the great pioneers of the study of radioactivity, who exposed him to the ongoing revolution in atomic physics.
He continued his European education as a Rhodes Scholar at Oxford University, under John Sealy Edward Townsend, a major figure in developing the study of the kinetics of electrons and ions in gases. Van de Graaff worked primarily on these topics at Oxford, where he was awarded a B.Sc. in 1926 and a Ph.D. in 1928. During this period, as he became aware of the work of ernest rutherford and others trying to fathom the mysteries of atomic structure, the pressing need for a high-energy subatomic particle accelerator, capable of disintegrating atomic nuclei, became increasingly clear to him. He realized that a high potential could be built up by storing electrostatic charge within a hollow sphere and that this could be achieved by depositing charges on a moving belt that carries the charges into the sphere, where a collector transfers them to the outer surface of the sphere. Van de Graaff’s idea led him to develop a device, now known as a Van de Graaff generator, that consisted of a large smooth metal sphere on top of a hollow insulating cylinder within which an endless insulating belt ran between pulleys at each end of the cylinder. Electric charge was sprayed from metal points connected to a high-voltage source onto the bottom of the belt; it was then carried up to the top of the belt, where it was collected by other metal points and accumulated on the outside of the sphere, causing it to become highly charged at a high electrostatic potential difference. Charged particles falling through this large electrostatic potential difference would then be accelerated to very high values of kinetic energy.
While at Oxford, Van de Graaff began working on designs for his generator. When he returned to the United States in 1929 he built his first working model, operating at 80,000 volts, at the Palmer Physics Laboratory at Princeton University, where he was a National Research Fellow from 1929 to 1931. He demonstrated an improved model, which operated at 1 million volts, at the inaugural dinner of the American Institute of Physics in November 1931.
That year he moved to Cambridge, Massachusetts, as a research associate at the Massachusetts Institute of Technology (MIT), where, in 1934, he would become an associate professor of physics. In an aircraft hangar in South Dartmouth, Massachusetts, he constructed his first large generator, able to produce 7 million volts, which was demonstrated on November 28, 1933. He developed the generator so that it could be used to accelerate subatomic particles to very high velocities. The previous year john douglas cockcroft and Ernest Walton had built the first particle accelerator, which produced the first nuclear transformations by means of artificially accelerated particles, at the Cavendish Laboratory at Cambridge. Van de Graaff’s machine was more compact, simpler in design, and capable of producing higher voltages (and, therefore, higher particle accelerations) than the Cockcroft-Walton accelerator.
In 1936, he married Catherine Boyden, with whom he would have two sons, John and William. Having obtained the patent for his generator, he began working with John G. Trump, a professor of electrical engineering at MIT, in designing a modified generator capable of producing X rays for treating cancerous tumors. It had its first clinical trial at Harvard Medical School in 1937.
During World War II, the U.S. Navy commissioned the production of five generators with a 2-million-volt capacity for use in the X-ray examination of munitions. With the experience of this work behind him, together with Trump, he was able to set up the High Voltage Engineering Company (HVEC), in 1946, for the commercial production of generators. The company developed the Van de Graaff generator for the wide variety of scientific, medical, and industrial research purposes it has today. Van de Graaff was honored with the Duddel Medal of the Physical Society of Great Britain in 1947.
Numerous improvements of the generator were to follow. The tandem principle of particle acceleration, developed by luis w. alvarez in 1951, was incorporated into a tandem version of the Van de Graaff machine, in which the high-voltage terminal is able to accelerate the ion twice. In the late 1950s, Van de Graaff invented a new insulating core transformer that generated high currents by using magnetic flux rather than electrostatic charging. He also developed techniques of controlling beams during and after acceleration, allowing physicists to adapt them for specific research needs. The improved accelerators yielded a mass of data on nuclear disintegrations and reactions, which led directly to advances in the theory of the atomic nucleus.
In 1960, he resigned from MIT in order to devote all his time to HVEC. He was awarded the American Physical Society’s Tom W. Bonner Award in 1966 for his generator.
Van de Graaff, who died in Boston on the morning of January 16, 1967, at the age of 65, left a substantial legacy to modern science and technology. Since its invention in the early 1930s, the Van de Graaff generator has played a vital role in many fields of physics, in astrophysics, and in medicine and industry.
