Differentiation of Performance‐Limiting Voltage Transients during Nb3Sn Magnet Testing

The Superconducting Magnet Group at Lawrence Berkeley National Laboratory has been developing high‐field, brittle‐superconductor, accelerator magnet technology for several years. While recent dramatic increases in Nb3Sn superconducting current density, (Jc = 3000 A/mm2 at 12 Tesla, 4.2 K) have facilitated the achievement of record peak dipole bore‐fields (16 Tesla), the number and size of fast intra‐coil flux‐adjustments of the “flux‐jump” variety have increased with the current density. In 2000, with state‐of‐the art (Jc = 2000 A/mm2 at 12 T) Nb3Sn conductor, the associated coil voltage transients were observed to be large enough to cause nuisance “quench‐detector” magnet‐protection false‐alarms. Subsequent Jc increases have resulted in large enough flux‐jumps to cause premature quenches in some magnets, at currents well below those predicted by their virgin strand superconducting “short‐sample” measurements.This paper will examine various types of quench‐onsets and their distinguishing characteristics. ...