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Spark of Genius

Robert Van de Graaff invented a high-voltage generator that helped lay the foundation for experimental particle and nuclear physics.
April 1, 2005

Whatever would robert have said?”

That’s not really a question. It’s the name of a song by a group called Van der Graaf Generator. In 1967, a handful of students at the University of Manchester named their band to honor the passing of physicist Robert Van de Graaff. Picture a rock band with an organ and saxophones, but no electric guitars.

Somehow, their musical unconventionality fit with Van de Graaff’s reputation as one of the world’s first atom-smashers. Early in his career, he developed interests in electricity and atomic physics—a mix of curiosities he picked up while working for the Alabama Power Company and, later, studying for a year at the Sorbonne, where he attended lectures by Marie Curie. By the time he was 28 and a researcher at Princeton, scientists were toying with the idea of examining the nuclear structure of the atom by hitting it with protons accelerated to high speeds. But they hadn’t yet figured out how to create an electric field large enough to fling the positively charged particles.

While others attempted to generate large electric fields with capacitors, Van de Graaff developed the machine for which he is still best known, the Van de Graaff electrostatic generator—essentially a big metal lollipop that crackles with hair-raising charge. Inside its tube-shaped body is a rubber or fabric conveyor belt that passes by a brush at the bottom, picking up positive charges and carrying them to an electrode at the top, inducing a positive charge in the metal bulb. Charge continues to stack up on the bulb’s surface, building greater and greater electric potentials that can propel a stream of positively charged particles released from a source inside the bulb. In popular-science demonstrations, however, the electric field is often used to create impressive sparks or raise the hair of a volunteer touching the metal sphere.

Van de Graaff joined MIT in 1931 and, with the support of university president Karl T. Compton, built a 13-meter-high, seven-million-volt version of the generator. This monster created an electric field that propelled particles through a vacuum tube that connected a 4.6-meter-wide bulb and a second bulb of equal size. Researchers were able to probe the nuclei of heavy atoms, conducting experiments that answered many fundamental nuclear questions and paved the way for the particle accelerators used today to study the basic building blocks of the universe.

Van de Graaff remained at MIT until 1960, refusing to leave even during World War II, when his department head urged him to lend his talents to the nuclear-research effort at Los Alamos. During those MIT years, Van de Graaff went on to develop other variations of his particle accelerator, including smaller versions that produced x-rays for such tasks as treating cancer patients or inspecting naval ordnance.

The technology survives in a modified form in some modern particle accelerators. Still, the original device’s simple, stark demonstration of electrical physics remains one of science’s most intriguing and informative teaching tools. Along with its familiar appearances in science fair and museum exhibits, the generator has found offbeat applications. Ensemble Robot, a music group founded by MIT grads, recently used the crackling generator as an instrument in a performance.

Whatever would Robert have said?

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