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UNITED STATES - NOVEMBER 15: 11 inch cyclotron, c 1931. the 11 inch at Berkeleyc, 1932. The cyclotron works by placing the source of the protons at the centre, between two D shaped cavities. When a proton passes from one cavity, or dee, to the other, and electric field accelerates it. Because the dees are in a magnetic field, the proton then travels in a semi-circle to reach the gap between the two dees once more. By then, if the direction of the electric field between the dees has changed, the proton accelerates once again. If this process is repeated, the proton gradually accelerates in a spiral. The vacuum chamber can be seen here. It lay flat between the poles of an electromagnet. (Photo by Science & Society Picture Library/SSPL/Getty Images)