Van de Graaff Generator

Our modern understanding of the nature of the atom stems from experiments done with particle accelerators. But behind every particle accelerator, there’s a power source.

On this day in 1931, Dr. Robert Van de Graaff of Princeton University unveiled a device that would help revolutionize physics. A New York Times reporter described the Van de Graaff generator. He wrote, “When the current for the motors is turned on, the belts of the two standards run rapidly up and down… After a few seconds a quiet crackling sound is heard, somewhat sharper than the rustling of leaves. This signifies that the potential of the spheres has become so high that they are discharging electricity…”

This discharge is much like a bolt of lightning. And, like lightning, it packs a huge punch. The power of a Van de Graaff generator can hurl atomic particles – – such as electrons, protons, or atomic nuclei — through a chamber at high speed. Thus the Van de Graaff generator — when used in particle accelerators — has helped reveal the parts of atoms — and thereby the underlying structure of the physical universe.

It’s said that Van de Graaff got the idea for his generator while still a student — while watching sparks fly from a printing press. Variations of the generator are still in use today in laboratories around the world. Our thanks today to the Research Corporation — since 1912, a foundation for basic scientific research.

Author’s Notes

A Van de Graaff generator is a device to make very high voltages. It works by generating static electricity, just as when you shuffle your feet on a rug and then touch a doorknob. For this generator, the belts look just like large car fan belts, and they are engineered to do this “footshuffling” very efficiently. Thus you can get very large voltages and very large sparks or, you can use the voltages to accelerate other charged particles, like atomic nucleii.

Van de Graaff’s device is a type of electrostatic generator. It builds up an electrical charge on two metal spheres — which can then be used to power a particle accelerator or high energy x-ray machines. Lower powered versions can make your hair stand on end in much the same way that rubbing your feet on carpet can, on a cold, dry day.

At the unveiling of the generator in 1931, a New York Time reporter wrote, “The 1,500,000-volt generator was placed in an alcove of the dining room. In appearance it might be taken for two identical, rather large floor lamps of modernistic design with the copper spheres as the lamp shades. A simple lamp cord running to the base of each glass standard bears out the illusion.”

Some work on the electrostatic generator was sponsored by Research Corporation in 1931. In fact, Research Corporation awarded numerous grants to Van de Graaff from 1931 to 1941. In 1933, with the aid of Research Corporation funds, Van de Graaff built and demonstrated the first large Van de Graaff generator. It was so large that it had to be housed in a blimp hangar at Round Hill, Massachusetts.

The spheres of this generator were each 15 feet 5 meters in diameter. The device “provided 20 times the output of any machine then known. It became the heart of one of the first powerful particle accelerators for probing matter.” Research Corporation Quarterly Bulletin, pg. 3 But it didn’t operate as well as hoped in open air and was later reconstructed in a pressurized chamber at MIT.

Van de Graaff patented his electrostatic generator in 1935.

Van de Graaff Dec. 20, 1901 – Jan. 16, 1967 received his M.S. degree in mechanical engineering from the University of Alabama in 1923 and his Ph.D. in physics from Oxford University Queen’s College in 1928. He was a Rhodes scholar. He returned to the United States in 1929 and began his serious research into electrostatic generators in 1931. In the 1930s and 1940s, Van de Graaff developed medical x-ray machines and x-ray machines for testing naval ordnance — both based on his patented generator. From 1934 to 1960, Van de Graaff was an associate professor of physics at MIT. In the 15 years following World War II, he was chief physicist for HVEC High Voltage Engineering Corporation, which manufactured commercial Van de Graaff generators as X-ray machines and particle accelerators.

More on the November 10, 1931 AIP dinner from New York Times article:

“The atomic nucleus, the storehouse of the vast energy of the atom, until now practically impenetrable by agencies controllable by science, has at last begun to yield to experiments which bid fair to disclose their inmost nature, it was said last night by Dr. Arthur H. Compton of the University of Chicago, Nobel Prize winner in physics, at a dinner given to scientists and newspaper men by the newly formed American Institute of Physics at the New York Athletic Club. …”

“Dr. Compton’s address was on the occasion of the first public demonstration of the 1,500,000-volt generator developed at Princeton University of Dr. Robert J. Van de Graaff, announced last week. Other generators of the same kind, capable of developing voltages up to 15,000,000, are to be built at Massachusetts Institute of Technology, and these new high-voltage machines, science hopes, will prove a tool with which to bombard the innermost part of the atom and make it give up its tremendous energy. …”

“Dr. Karl T. Compton, president of Massachusetts Institute of Technology, and chairman of the governing board of the American Institute of Physics, spoke briefly about the newly formed institution, established on Oct. 1 by the American Physical Society, the Optical Society of America, the Acoustical Society of America, and the Society of Rheology, to act ‘as an agent for cooperation by the four societies in the interests of physics.'”

” ‘The primary objects of the Institute,’ said Dr. Compton, ‘are threefold: It will devote itself to the problem of making available to the public more and more accurate information concerning the developments in pure and applied physics. To this end it will try to facilitate the close cooperation between newspapers and scientific institutions. It will also study the problems of scientific journals and will make contacts between presently unrelated groups of physics workers.’ …”

Sources for more info:

  • Research Corporation Quarterly Bulletin, Spring, 1982
  • “Atom Nucleus Seen Yielding to Science … 1,500,000 Volts Leap From 90 Device in Test Before the American Institute”, New York Times, Late City Edition, Vol. LXXXI, No. 26,954, November 11, 1931, pg. 1, 17
  • “Dictionary of American Biography, Supplement Eight, 1966-1970”, John Garraty, Mark C. Carnes, ed.s, Charles Scribner’s Sons, 1988, pgs. 665-666
  • Center for History of Physics, American Institute of Physics –
  • A Short History of the American Institute of Physics –
  • Images of Robert van de Graaff From the Emilio Segre Visual Archives at the AIP

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