Analysis of observations during operation of the NHMFL 45-T hybrid magnet system

Abstract

The NHMFL hybrid magnet system, which was designed to produce steady field in excess of 45 T in a 32-mm, room-temperature bore, was first tested in December 1999. Since then, the system has served users of the NHMFL at the full design currents in both the superconducting outsert (10 kA) and the resistive insert (67 kA), reaching a combined field of 45.2 T. This magnet system combines both superconducting and resistive magnet technologies, which, whether taken together or separately, define new states of the art. Operating alone, the superconducting outsert has been charged repeatedly to 10 kA, corresponding to a maximum field of nearly 16 T at its 710-mm winding i.d. More recently, operation of the outsert has been limited to 8 kA as a consequence of degradation suffered during an “unprotected” quench, but insert upgrades and higher-current operation (up to 74 kA) have allowed the system to provide 45 T to users still. Because the system was designed from the outset as a facility rather than an experiment, there is a minimum of instrumentation––in fact there is none internal to the steel vessel housing the superconducting magnet. Therefore, projections of internal conditions in the superconducting magnet are deduced from detailed analysis of observations from coil voltage taps and various external temperature sensors and pressure transducers. We present these with comments regarding their value in future magnet design as well as an introduction for more complete analysis by complex computer codes.