The comparison of active and passive cancellation coils for SSTF

The Samsung superconducting test facility (SSTF) at SAIT (Samsung Advanced Institute of Technology, Taejon, Korea) is to be equipped with a 740 mm inner diameter superconducting split magnet (MC), which provides the background field B₀ = 8 T with ramp rate up to 3 T/s at 250 mm gap between the magnet halves. A smaller superconducting split magnet (BC) with the diameter 400 mm will be installed coaxially inside of MC to produce an additional fast variation of magnetic field with ramp rate up to 20 T/s and amplitude ±1 T. In order to reduce the coupling between MC and BC magnets and to avoid the MC disturbance by the fast changing stray field from BC a cancellation coil (CC) is to be provided. The comparison of an active superconducting CC charged in series with BC and a passive cryoresistive, LHe cooled CC (PCC) of which the current is induced during the fast BC discharge only has been made. The advantages of the PCC concept are discussed. The amount of LHe evaporated by PCC (charged for a short time) is estimated to be 3 to 5 liter/pulse. Recovering time for PCC is 5 to 10 min.