 When the particles reach the terminal, they are stripped of some electrons to make them positively charged and are subsequently accelerated by repulsive forces away from the terminal.This configuration results in two accelerations for the cost of one Van de Graaff generator, and has the added advantage of leaving the complicated ion source instrumentation accessible near ground potential.The voltage produced by an open-air Van de Graaff machine is limited by arcing and corona discharge to about 5 megavolts.