Field Mapping of the IUCF 200 MeV Cyclotron

Magnetic field mapping of the Indiana main stage cyclotron is performed on a Cartesian grid using a 4 by 4 array of Hall probes. The apparatus, driven by torque motor-assisted, high-speed stepping motors, maps one eighth of the cyclotron beam area in 6 hours. Positioning accuracy is maintained by encoders attached to the stepping motor drive shafts and absolute probe locations are determined using magnetic fiducials on the magnet pole tip. The mapper is interfaced to a digital computer for automatic position control and for field data acquisition, reduction and storage. On-line data reduction includes conversion of Hall voltages to field values, allowing for individual differences in the sensitivity and non-linearity of the probes, and corrections in the fields for measured errors in the relative probe positions. Examples of the field data quality obtained are presented.