Upgrade of the NHMFL Cryogenic System and the Index Heating Test Results on the 45-T Hybrid

The 45-T Hybrid at the National High Magnetic Field Laboratory (NHMFL) has been the only facility in the world capable of providing a dc field of above 40 T. The 45-T hybrid magnet, consisting of a superconducting outsert and resistive insert, was commissioned in 2000 reaching a field of 45 tesla. The cryogenic system for the NHMFL has been in service since 1994 and has provided cryogenic service for the 45-T hybrid superconducting outsert since testing in 1998. It was recently upgraded, replacing a majority of the original system. The 45-T Hybrid was cooled down successfully with the new cryogenic system in February 2014. The new cryogenic system has been proved more efficient and reliable in the past years, providing increased availability to the users. After the upgrade of the cryogenic system, a standard index heating test was performed on the outsert of the hybrid. This test is mainly for evaluating the performance of the outsert, particularly the degradation of the innermost Nb3Sn coil of the outsert that suffered an unprotected quench in 2000 and degradation since then. The results of index heating tests in the past are compared and presented.