Did you know?
Cyclotrons are not just used for new physics experiments, they are being used in hospitals and cancer centers around the world. They are used in radiation therapy for cancer patients. On one hand they are being used to create radio-isotopes which are used in the imaging process so they know exactly where the cancer is, and also to shoot proton beams at the cancer to destroy it. 4

The design for a circular accelerator by Ernest Lawrence (1929), 2 the cyclotron consists of a central particle source and two 'D' shaped electrodes (called "dees") encased in a vacuum chamber placed in a uniform magnetic field. The dees consist of two parallel semicircular plates, separated by a gap and joined along their curved edge by a plate perpendicular to both 'D' plates. The straight edge of the dee is left open and the inside hollow. By aligning the two dees such that they form a circle, with their straight edges parallel and their open hollows facing each other as in the figure at right, and placing the particle source within this hollow, a voltage can then be applied across the gap between the dees by inducing a charge in one dee and an opposite charge in the other dee. This voltage results in no net force while the particle is within the hollow of the dee, but a force that does work on the particle to accelerate it while it is in the gap between the dees. 15 This is due to the electric field caused by the potential difference between the dees.

Cyclotron Patent Schematic
Original Cyclotron Patent Schematic 3

Placing the entire vacuum chamber between the poles of a large circular magnet introduces a magnetic field, which accelerates a charge within the dees perpendicularl y to its velocity according to the Lorentz force law. 16 This creates a circular motion of the particle, causing it to circulate within the dees. As such, it crosses the gap between the dees twice every cycle. This being the case, the charge on the dees must be switched between crossings, or else the particle would accelerate on one crossing and decelerate on the next. This introduces the requirement for oscillating electric fields. As such, the dees are connected to an oscillating electric circuit, which causes the oscillating charge in them and causes the oscillating electric field.