The exit port provides an outlet to which apparatus or a suitable beam line can be connected to deliver the accelerated beam to a target. Displayed above is a schematic representation of the accelerating tube inside the Van de Graaff linear accelerator. Although not shown above, the ion source is part of the terminal of the machine and sits at whatever voltage is applied to the terminal. The terminal voltage is obtained by storing charge on the terminal dome. The more charge stored, the higher the terminal voltage becomes.
Charge is brought up from the base plate power supply via an insulated rotating belt.
The belt is conveyed by two pulleys, one at the base and the other at the terminal. Charge is placed on the belt at the base pulley and removed at the terminal pulley by stainless steel screens, which are positioned so that they just touch the moving belt. The amount of charge stored on the terminal dome is controlled by three factors. Without this gas, the high voltages needed could not be achieved. The process is started by allowing a controlled leak of H 2 gas to enter the source bottle.