MODEL RELEASED. Plasma sphere. Metal ball at the centre of a plasma sphere. The ball has a very high electrical voltage applied to it. This causes a large potential difference between the sphere and the spherical glass globe that surrounds it (not seen). The globe contains gas at low pressure. Static discharges across the gas cause the atoms in the gas to lose their electrons, turning the gas into a plasma. When the nuclei and the electrons recombine they emit the light seen here. Touching the outside of the glass globe concentrates the static charge on the glass, intensifying the ionising field and causing the streamers of light.