Hi. I have access to following Leybold Van de Graaff generator: The instructions and data sheet can be found here, but they don't give much insight. I have found different working principles of VdG generators. Some need the rising and falling sides of the belt to be closely together from top to bottom to act as a capacitor, others don't rely on this at all. I haven't found other descriptions of VdG generators like this one where the sides are brought together only at one point (6). I thought it might be an improvement to the following kind of VdG generators: They might have brought together both sides of the belt where they placed the lower electrode such that more positive charge gets attracted to the outside of the belt (since now there's more negative charge on the inside of the belt close to the electrode). However, I found that the dome actually gets charged negatively. Also, all three rollers seem to be made of the same kind of plastic.