Gary Schmitt, age 16, of Mesa, Ariz., for his question:

WHAT IS A VAN DE GRAAFF GENERATOR?

A Van de Graaff generator is a device for building up high electric charge. It is also called an electrostatic generator. It is a source of changed particles that may be used for atom smashing.

The Van de Graaff generator is used to boost protons and other nuclear particles to energy of about 10 million electron volts. The chief value of the machine is that narrow beams of protons of known energies can be produced. These beams are used to study nuclear forces.

A scientist named Robert J. Van de Graaf made the first generator of this kind at the Massachusetts Institute of Technology in 1931.

In the generator, a continuous belt of an insulating material moves past a source of negative electricity. This source sprays electrons on the belt. The belt then goes into a hollow metal dome where a fine metallic brush moves the electrons onto the dome surface. When the charge at the top of the dome is high enough, electrically charged particles are hurled at targets at the bottom of the generator.

Van de Graaff machines work at higher energy when they are enclosed in pressure vessels.