Commissioning and Operational Experience from FRIB Target and Fragment Pre-separator Superconducting Magnet Quench Management System

Abstract

The target and fragment pre-separator segment of the continuous wave heavy ion beam linear accelerator at FRIB consists of fourteen superconducting magnets. These magnets have (4.5 K) cold masses ranging from 0.8 up to 22.5 metric tons, and the combined liquid helium inventory stored is approximately 8000 L. All of these superconducting magnets have been cooled down (to 4.5 K), trained, and are presently being operated. While operational, these magnets can have a stored (magnetic) energy ranging from several hundred kilojoules, up to 1.3 mega-joules. The thermal energy and boil-off flow released during quench in these magnets are handled using a system unique to FRIB, and a concept that was originally developed and successfully demonstrated at the Superconducting Super-Collider Lab (SSCL) for the magnet string test in 1993. This quench management system developed at FRIB consists of a 10,000-L liquid helium dewar (buffer vessel) and associated cryogenic distribution system. It has provided a robust and stable operation for the superconducting magnets during training and normal operations, while persevering the helium inventory and allowing a quick turnaround time for operation and availability. The observed effect of magnet quenches on the FRIB cryogenic system (including the 4.5 K helium refrigerator and sub-atmospheric helium refrigerator) is presented and discussed.