An Air-Core Type Superconducting Quadrupole Triplet for the BigRIPS Separator at RIKEN

The BigRIPS fragment separator in the RIKEN RI beam factory has an air-core type superconducting quadrupole triplet as the first focusing element. The quadrupole triplet consists of three air-core superconducting coils having effective lengths of 500 mm, 800 mm, and 500 mm, and the maximum field gradients of 24 T/m, 20 T/m, and 20 T/m. All three quadrupoles are assembled into a single cryostat and cooled by liquid-helium bath cooling using a cryogenic plant. The coils have a flat racetrack shape and their warm bore radii are 90 mm, 120 mm, and 120 mm. Its cryostat characterized by gas-cooled current leads with multiple electrodes is also discussed.