Round Hill generator

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The Round Hill generator is an early high‑voltage Van de Graaff accelerator built in Round Hill, Massachusetts, and finished in 1933. It was meant to be the world’s most powerful particle accelerator and is now on display at the Boston Museum of Science for educational demonstrations. It was created by an MIT team led by physicist Robert J. Van de Graaff, who hoped the device would enable artificial splitting of the atom, a goal reached a year earlier by Cockcroft and Walton.

The machine stood about 43 feet tall and used two large aluminum spheres (each 15 feet in diameter) mounted on tall insulating columns. A belt system charged the spheres, storing electricity until it could be released through a vacuum tube between the spheres. The design aimed for 10 million volts, but air insulation and other factors limited it to about 5.1 million volts, with the entire setup capable of delivering a few milliamps of current. Because it required careful environmental control, the generator was housed in an airship hangar at Round Hill, where spectacular lightning discharges earned it the nickname “an electrical Niagara.” Pigeons, humidity, and salt spray from the coast also hindered its performance, and no nuclear experiments were completed there.

In 1937 the generator was moved to MIT’s campus in Cambridge and rebuilt as a more compact, enclosed machine with improved charging systems and a remote-control setup. It operated at lower but more stable voltages (up to about 2.4 MV) and was shielded for radiation safety. After about two decades at MIT, the machine was moved again in 1955 to the Boston Museum of Science, where it became the centerpiece of the Theater of Electricity and a popular educational exhibit.

The Round Hill project helped prove that very high, controllable voltages could be produced electrostatically and used to study atomic nuclei. The work spurred further development of high‑voltage accelerators and contributed to the formation of the High Voltage Engineering Corporation, which produced many accelerators for research and medical use. The Round Hill generator thus played a crucial early role in the history of particle acceleration and its applications.