Synchrocyclotron

By the time cyclotron-accelerated particles reached energies of 20 MeV, their mass increased so much that they curved less sharply. McMillan worked out a method for synchronizing the magnetic field in such a way that the alternations of the magnetic field slowed and kept time with the mass increase of the particles.
 Edwin Mattison McMillan and Vladimir lositovich Veksler United States and Russia 1945 Synchrocyclotron

By the time cyclotron-accelerated particles reached energies of 20 MeV, their mass increased so much that they curved less sharply. McMillan worked out a method for synchronizing the magnetic field in such a way that the alternations of the magnetic field slowed and kept time with the mass increase of the particles.