Numerical modelling of the cool-down of the helium transfer-lines for FRIB LINAC and experimental systems

Abstract The cryogenic distribution system at FRIB is extensive, encompassing three Linac segments, fourteen experimental system superconducting magnets, cross-connect between FRIB and the reconfigured NSCL legacy system, and the A1900 magnets, as well as many other user experimental loads. The cool-down or warm-up of these transfer-lines is an inherently transient process and must be conducted at a gradual enough rate to keep local temperature gradients and corresponding thermal stress on the piping system within acceptable limits. To this end, estimation of this transient process is very helpful in operational planning. A two temperature (fluid and pipe wall) model was developed to capture the transient characteristics of the cool-down or warm-up process with real fluid properties, and considering the effects of heat in-leak, momentum, flow resistance, and piping components. It was employed to estimate the cool-down of different FRIB transfer line sections, and the results were compared against data obtained during actual cool-down of the transfer line.