Process design for FRIB’s experimental refrigeration system

Abstract

The experimental system (ES) for the Facility for Rare Isotope Beams (FRIB) at Michigan State University (MSU) has several segments. Following the acceleration through the three superconducting LINAC segments, the heavy ion beam is guided through the target, a fragment pre-separator and (the A1900) separator segments. There are many beam lines and then it can be split and sent to various experimental vaults and instrumentation, e.g. S800 spectrograph, and the newly proposed High Rigidity Spectrometer (HRS). Presently, superconducting magnets at the target and fragment pre-separator segments, along with the LINAC superconducting cryo-modules, are supported by FRIB’s main central helium liquefier/refrigerator (CHL). The remainder of the cryogenic loads are supported by the legacy NSCL Cryogenic Refrigerator (a re-commissioned Bureau of Mines helium liquefier from the mid 1970’s) and has many obsolete components for reliable operation. Considering the operational reliability of the accelerator, maintainability of the entire cryogenic system at FRIB and ever-growing experimental beam lines – it is logical to segregate the experimental system loads from the accelerator system loads. A new 4.5 K refrigerator along with a thermal shield (55 K) refrigerator are planned to support the operation of these experimental system (ES) loads and make plans for the CHL maintenance. These refrigerators will be able to support a combination of 4.5 K isothermal refrigeration, 4.5 K liquefaction (for magnet lead cooling and transients) and thermal radiation shield loads. The design loads, modes of operation and the planned operation of the FRIB cryogenic system with these refrigeration systems are discussed. This paper outlines the key selection parameters and design modes for the major components, such as the warm compressors, turbo-expanders and heat exchangers.