December 20, 1901, Tuscaloosa, Alabama (United States) – January 16, 1967, Boston (United States)
Robert Jemison Van de Graaff obtained his bachelor's and master's degrees in Physics at the University of Alabama, studied for a few years at the Sorbonne University (Paris, France), and received his doctorate in Philosophy, in 1928, at the University of Oxford (England), with a Rhodes scholarship, under the supervision of John Sealy Townsend (great mathematical physicist who studied the electrical conduction of gases and directly measured the electrical charge).
Upon his return to the United States, he first worked at Princeton University and then, in 1931, joined the staff of the prestigious Massachusetts Institute of Technology (MIT) as a research fellow. In 1934, he became an associate professor until he retired in 1960.
His research focused on nuclear physics and he invented electrostatic generators (which bear his name) that produced high voltages for the study of atomic particles. His first design, in 1929, produced 80,000 volts, but with successive modifications, in 1933, he achieved a larger generator that generated 7 million volts.
In 1936, he was awarded the Elliot Cresson Medal.
During World War II, he was director of the High Voltage Radiographic Project and, after it ended, he co-founded the High Voltage Engineering Corporation (HVEC) with John G. Trump (known for the development of radiotherapy).
In the 1950s, he invented the insulating core transformer, which produced high-voltage direct current, and tandem generator technology.
In 1965, he was awarded the T. Bonner Prize by the American Physical Society for the development of electrostatic accelerators.
Van de Graaff generator
It uses an insulating motorized strap, usually made of rubber, to conduct electrical charges from a high-voltage source at one end of the strap into a metal sphere at the other end. Since the electrical charge resides on the outside of the sphere, it accumulates to produce an electrical potential much greater than that of the primary high-voltage source.
You have practical limitations on the potential produced by these generators at about 7 million volts. However, with tandem generators, which are essentially two generators in a series, around 15 million volts can be produced.
They are mainly used as direct current power supplies for linear atomic particle accelerators used for nuclear physics experiments.
Due to the simplicity of their design and their theoretical foundation, they are built, on a small scale, by hobbyists and companies to demonstrate the effects of the high potentials of direct current, since even these small machines produce impressive sparks several centimeters long.
The world's largest air-insulated generator was built by Van de Graaff himself and is in operation at the Boston Museum of Science.
Most modern Van de Graaff generators are insulated by pressurized dielectric gas (freon or sulfur hexafluoride).
Over the last few years, their design has evolved and generators have slowly been replaced by solid-state DC power supplies with no moving parts.
Atomic or particle Van de Graaff accelerators
They are devices used to increase the speed of subatomic particles, such as protons, electrons, and positrons.
Van de Graaff's design consists of a tall metal cylinder with a hollow metal dome at its top. Through the center of the cylinder, a silk conveyor belt moves positive charges gathered from a high-voltage source to the top of the cylinder, where they are deposited on top of the dome. The longer the tape, the more positive charges accumulate.
At a given moment, the charges accumulated on the hollow dome are so high that an electrical discharge jumps from the dome to the metal bar located near the device, thus expelling the charges from the dome.
To convert this accelerator into a particle accelerator, it is only necessary to install a type of target on the metal bar and when the electric discharge hits it, it will bombard the target whose atoms will be separated due to the positively charged beam of electricity. The speed of the discharge from the dome to the target will increase from zero to more than 160,000 km/s in the space between the two points.
Linear accelerators (linacs) work on the same principle, except that a particle is exposed to a series of electric fields, each of which increases its speed.
Initially, it could produce an accumulation of charge with an energy of 80,000 volts, although later improvements raised this value to 5 million volts. They were designed to study the basic structure of matter, however, several practical applications were later discovered.
Newer accelerators employ different technologies and produce much higher energies, so Van de Graaff accelerators are virtually obsolete as they are only used, and only to a limited extent, for graduate student research in colleges and universities or as sources of energy ions for high-energy explosions.
