Particle-beam Van de Graaff accelerators are often used in a "tandem" configuration: first, negatively charged ions are injected at one end toward the high potential terminal, where they are accelerated by attractive force toward the terminal. When the particles reach the terminal, they are stripped of some electrons to make them positively charged and are subsequently accelerated by repulsive forces away from the terminal. This configuration results in two accelerations for the cost of one Van de Graaff generator and has the added advantage of leaving the complicated ion source instrumentation accessible near ground potential.

#VandeGraaffAccelerators, #ParticleBeamAccelerators

The voltage produced by an open-air Van de Graaff machine is limited by arcing and corona discharge to about 5 MV.

#CoronaDischarge

A corona discharge is an electrical discharge caused by the ionization of a fluid such as air surrounding a conductor carrying a high voltage. It represents a local region where the air (or other fluid) has undergone electrical breakdown and become conductive, allowing charge to continuously leak off the conductor into the air. A corona occurs at locations where the strength of the electric field (potential gradient) around a conductor exceeds the dielectric strength of the air. It is often seen as a bluish glow in the air adjacent to pointed metal conductors carrying high voltages, and emits light by the same mechanism as a gas discharge lamp.