I was pleased to see the photo of the Oak Ridge Pelletron on the cover of the August 2010 issue of Physics Today. The 25URC Pelletron, made by National Electrostatics Corp (NEC) in Middleton, Wisconsin, was delivered to Oak Ridge National Laboratory around 1980. The man in the cover photo is Dan Stark, an electrical engineer who worked for NEC at the time.
It’s unfortunate that the photo caption refers to the accelerator as a Van de Graaff. Although Robert Van de Graaff may have first developed the concept of electrostatic charging to high voltage, his contemporary, Raymond Herb, working here at the University of Wisconsin-Madison physics department, spent many years perfecting a much better accelerating tube, column structure, and charging system. Herb founded NEC in 1965 to build Pelletrons, named after the NEC charging chain that replaced the Van de Graaff rubber belt.
Van de Graaff’s company, High Voltage Engineering Corp, sold a great many belt-charged Van de Graaff accelerators, but the 25URC NEC Pelletron at Oak Ridge holds the records for the highest sustained DC voltage ever achieved, about 30 MV, and the highest terminal potential while running an ion beam, 25.5 MV for Ni+13 at 357 MeV. The 25URC has accelerated heavier ions to about 600 MeV.
The 25URC at Oak Ridge was one of the first accelerators I worked on after I started at NEC in 1977. I no longer work there, but I respect its product and believe that appropriate credit should go to the late Ray Herb and to NEC for that remarkable device.
