Magnetization and Creep in YBCO Tape and CORC Cables for Particle Accelerators: Value and Modification Via Preinjection Cycle

Abstract

High-temperature superconductors (HTSs), including YBCO coated conductors, are being considered for high field dipole and quadrupole magnets for future particle accelerators. The quality of the magnetic field generated by the magnet and its temporal stability are important considerations. The persistent current magnetization of superconductors can degrade the field quality of the magnetic field generated by magnets made from them by causing error fields, and flux creep in the superconductor may lead to drift in the value of the magnetic field during magnetic field ramp holding sequences, including at particle injection. HTS composites possess larger persistent current magnetizations and larger flux creep than low-temperature superconductor composites, and therefore, the error fields and any temporal change of them are typically larger. In this paper, the 4.2 K magnetization of a small segment of coated conductor was measured in a vibrating sample magnetometer in perpendicular fields up to 14 T, and the decay was measured at 1 T. The magnetization and decay of a CORC cable were measured in a 12 T cryogen-free magnet. A Hall sensor, placed close to the sample, was used to measure the magnetization. The applied magnetic field was ramped through full flux penetration, and then, brought within one flux penetration depth of the target applied magnetic field before the decay measurement was started. Selective cycling of the magnetic field applied to the samples was explored as a technique to reduce the magnetization and its decay. Significant suppression of both the initial magnetization at 1 T and its decay were observed.