Development of a thin-wall superconducting magnet for the positron spectrometer in the MEG experiment

A thin-wall superconducting magnet was developed for the positron spectrometer in the MEG experiment. The magnet is specially designed to provide a gradient magnetic field to achieve good features of the spectrometer such as constant projected bending radius for monochromatic positrons and much quicker sweep of positrons than in the conventional uniform solenoidal field, which allows a stable operation of the spectrometer in a high rate muon beam. A high-strength aluminum-stabilized conductor was developed so as to minimize the thickness of the coil between the target and photon detector. A pair of compensation coils is implemented in the magnet to cancel stray field around the photon detector to be placed closely to the magnet. Design of the magnet and results from the excitation tests to measure performance of the magnet will be presented here.