The polar co-ordinate magnetic measuring system for the axial field spectrometer magnet at the ISR-CERN

A system for the measurement of three-dimensional magnetic fields with nearly axial symmetry is described. The apparatus, which was used for the mapping of the field volume in the axial field spectrometer magnet of the ISR, measures in polar co-ordinates. The choice of the co-ordinate system and its advantages over other possible configurations is explained with particular reference to the measured magnet. The design and operation of the measuring system is described in detail, and its performance is discussed.