Magnetic Field Measurements in the MSU 500 MeV Superconducting Cyclotron

The measurements of the magnetic field in the superconducting cyclotron under construction at Michigan State University are reported. The 55-channel flip coil gaussmeter built at MSU for this purpose is described. Twelve field maps measured with various currents in the two sections of the main coil have been Fourier-analyzed for evaluation of magnetic imperfections and data errors and for comparison with calculated magnetic field distributions. The calculation procedure is in excellent agreement with the measured data. The imperfection harmonics are small and there is evidence in the measurements that they are partly correctable by better alignment of pole tips and coil tank at final assembly of the cyclotron.