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A hollow D-shaped electrode that shields a circulating ion from the accelerating electric field during one half-turn. Two opposed cyclotron dees provide two shielded regions separated by a gap; their electric potential difference alternates. The vacuum reduces collisions with residual gas. An ion source supplies particles near the center, and an extraction system directs an outer orbit toward a particle detector or target. Useful electric current depends on retaining particles near the median plane and delivering them to the outlet, as well as on increasing their kinetic energy.

An electrostatic accelerator gives a charged particle kinetic energy by taking it through a sustained electric potential difference. Its ion source, accelerating tube and target form a particularly direct chain: prepare a charge, let an electric field do work, and measure what arrives or what the target emits. A vacuum reduces collisions with gas before the beam reaches its target. The Cockcroft-Walton generator supplies the potential by accumulating electric charge on capacitors.