The cyclotron is a device used to provide high energy beams for particle accelerators used in research and in hospitals for radiation therapy. The cyclotron consists of two D-shaped electrodes (dees) in a vacuum chamber placed in a magnetic field perpendicular to the plane of the dees. High frequency a.c. is applied to the dees so that charged particles are forced into a circular path. On emerging from one dee the particle is accelerated across the gap and travels in a circle with a larger radius thus following a spiral path and emerging from the cyclotron with a much greater speed.