<P> A more recent development is the tandem Van de Graaff accelerator, containing one or more Van de Graaff generators, in which negatively charged ions are accelerated through one potential difference before being stripped of two or more electrons, inside a high - voltage terminal, and accelerated again . An example of a three - stage operation has been built in Oxford Nuclear Laboratory during 1964 of a 10 MV single - ended "injector" and a 6 MV EN tandem . </P> <P> By the 1970s, as much as 14 million volts could be achieved at the terminal of a tandem that used a tank of high - pressure sulfur hexafluoride (SF) gas to prevent sparking by trapping electrons . This allowed the generation of heavy ion beams of several tens of megaelectronvolts, sufficient to study light ion direct nuclear reactions . The greatest potential sustained by a Van de Graaff accelerator is 25.5 MV, achieved by the tandem in the Holifield Radioactive Ion Beam Facility in Oak Ridge National Laboratory . </P> <P> A further development is the pelletron, where the rubber or fabric belt is replaced by a chain of short conductive rods connected by insulating links, and the air - ionizing electrodes are replaced by a grounded roller and inductive charging electrode . The chain can be operated at much greater velocity than a belt, and both the voltage and currents attainable are much greater than with a conventional Van de Graaff generator . The 14 UD Heavy Ion Accelerator at the Australian National University houses a 15 - million - volt pelletron . Its chains are more than 20 meters long and can travel faster than 50 kilometres per hour (31 mph). </P> <P> The Nuclear Structure Facility (NSF) at Daresbury Laboratory was proposed during the 1970s, commissioned during 1981, and opened for experiments during 1983 . It consisted of a tandem Van de Graaff generator operating routinely at 20 MV, housed in a distinctive building 70 m high . During its lifetime, it accelerated 80 different ion beams for experimental use, ranging from protons to uranium . A particular feature was the ability to accelerate rare isotopic and radioactive beams . Perhaps the most important discovery made using the NSF was that of super-deformed nuclei . These nuclei, when formed from the fusion of lighter elements, rotate very rapidly . The pattern of gamma rays emitted as they slow down provided detailed information about the inner structure of the nucleus . Following financial cutbacks, the NSF closed in 1993 . </P>

How much work does the electric motor of a van de graaff generator