Principle. It is based on the following two facts:
(i) If a charged conductor is in internal contact with another hollow conductor, the hollow conductor accepts all available charge on the charged conductor irrespective of its own potential.
(ii) The electric discharge takes place in air or gases readily at pointed conductors.
Construction: A large hollow metallic sphere S is mounted on two. insulating columns CC' as shown in Fig. An endless belt of an insulating material is made to run on two pulleys P1 and P2 with the help of an electric motor. The metal comb C1, called spray comb is held near the lower end of the belt. When it is maintained say at high positive potential with the help of H. T. source (≈ 104V), it produces ions in its vicinity. The positive ions get sprayed on the belt due to the repulsive action of comb C1, which are carried upward by the moving belt. A comb C2 called collection comb is positioned near the upper end of the belt such that the pointed end touch the belt and the other end is in contact with the inner surface of the metallic sphere S.
Working: The comb C2 collects the positive ions and transfers them to the metallic sphere. The charge transferred by the comb C2 immediately moves on to the outer surface of the hollow sphere. As the belt goes on revolving continuously the accumulation of positive charge on the sphere also keeps on taking place and its potential rises considerably. With the increase of charge on the sphere, its leakage due to ionisation of surrounding air also becomes faster. The maximum potential to which the sphere can be raised is reached, when the rate of loss of charge due to leakage becomes equal to the rate at which the charge is transferred to the sphere. To prevent the leakage of charge from the sphere, the generator is completely enclosed inside an earth-connected steel tank which is filled with air under pressure.
If the projectiles such as protons, deuterons etc. are now generated in the discharge tube D with lower end earthed and upper end inside the hollow sphere, they get accelerated down the tube due to the high potential difference. On leaving the discharge tube at the other end, they hit the target with large kinetic energy and bring about nuclear disintegration.
