MULTIPOLAR MAGNET FOR LOW-FREQUENCY ESR IMAGING

Low-frequency ESR imaging requires field configurations which are difficult to obtain using traditional electromagnets. Multipolar magnets represent a convenient way to obtain the main magnetic fields and two of the three gradients necessary for a 3D image reconstruction. We present the first experimental implementation of this design in the form of a 16-pole electromagnet of cylindrical symmetry, with an aperture of 27 cm and a length of 60 cm. To achieve a given field profile the currents at each pole must be individually controlled and the whole experiment must be under computer control. The power supply consists of 16 bipolar sections that deliver 10 A through a load of 3.7-OMEGA. The field is sensed by Hall probes at the 16 pole positions and this information is used to correct the field. Details are provided of the power supply and of the interface between power supply and computer.