Answer: [Figure: van de Graaff generator]
The labelled diagram shows:
- a large hollow metal sphere (spherical shell) at the top, mounted on an insulating column;
- an endless belt of insulating material (rubber/silk) running over two pulleys, the lower pulley driven by an electric motor and the upper one inside the sphere;
- a spray comb (lower comb) near the bottom of the belt, connected to the positive terminal of a high-tension (H.T.) source, which sprays positive charge on the belt;
- a collecting comb (upper comb) near the top of the belt, connected to the inner surface of the sphere, which transfers the charge to the sphere;
- a discharge (accelerating) tube with the ion source at the top inside the sphere and the target at the bottom, which is earthed;
- the whole set-up enclosed in a steel chamber filled with nitrogen/methane at high pressure to reduce leakage of charge.
