Superconducting sector magnets are to be the main components of the superconducting ring cyclotron for the RIKEN RI beam factory. The sector magnet has superconducting main and trim coils. A cryogenic stabilization method is applied to both coils in order to make them quench-free. Both superconducting coils and their wires, design of stabilization, quench simulation, and measurement of the stabilized currents using small test coils are described.
