A cyclotron that includes a magnet yoke having a yoke body that surrounds an acceleration chamber. The cyclotron also includes a magnet assembly to produce magnetic fields to direct charged particles along a desired path. The magnet assembly is located in the acceleration chamber. The magnetic fields propagate through the acceleration chamber and within the magnet yoke, wherein a portion of the magnetic fields escapes outside of the magnet yoke as stray fields. The cyclotron also includes a vacuum pump that is coupled to the yoke body. The vacuum pump is configured to introduce a vacuum into the acceleration chamber. The magnet yoke is dimensioned such that the vacuum pump does not experience magnetic fields in excess of 75 Gauss.