Cyclotrons accelerate charged particles using oscillating electric fields generated between hollow metal chambers called dees. A positive ion is placed between the dees and accelerated toward the first dee when it is negatively charged. It follows a semicircular path due to a strong magnetic field until the dee polarities are reversed, accelerating it toward the second dee and to higher energies with each pass through the oscillating field. Cyclotrons can be used to accelerate ion beams for nuclear physics experiments and cancer treatment through proton therapy.