Mathematical Modeling of a Fermilab Helium Liquefier Coldbox

Abstract

The Fermilab Central Helium Liquefier (CHL) facility is operated 24 hours-a-day to supply LHe at 4.6"K for the Fermilab Tevatron superconducting proton-antiproton collider Ring and to recover warm return gases. The centerpieces of the CHL are two independent cold boxes rated at 4000 liters/hour and 5400 liters/hour with LN2 precool. These coldboxes are Claude cycle and have identical heat exchangers trains, but different turbo-expanders. The Tevatron cryogenics demand for higher helium supply from CHL was the driving force to investigate an installation of an expansion engine in place of the Joule-Thompson valve. A mathematical mode1 was developed to describe the thermo-and gas-dynamic processes for the equipment included in the helium coldbox. The mode1 is based on a finite element approach, opposite to a global variables approach, thus providing for higher accuracy and conversion stability. Though the coefficients used in thermo-and gas-dynamic equations are unique for a given coldbox, the genera1 approach, the equations, the methods of computations, and most of the subroutines written in FORTRAN can be readily applied to different coldboxes. The simulation results are compared against actual operating data to demonstrate applicability of the model.

Lessons from commissioning and operations of the ICARUS cryogenic system at Fermilab

“…In Icarus, this was achieved by first pumping the empty cryostats to high vacuum for 9 months to remove a bulk of contamination from surfaces by desorption. In addition, an elaborate filtration system had to be installed and prepared (Geynisman et al, 2021) to remove the remaining impurities, mostly from the initial fill and continuing outgassing of impurities from the materials inside the cryostats and recapturing them into liquid argon bath during operations.…”

“…The initial commissioning of the cryogenic system and fill of the Icarus cryostats occurred in mid-2020 (Geynisman et al, 2021). While the system reached the overall thermal and pressure stability in a relatively short period of time, the free electrons lifetime slowly improved from the initial values of τ = ~1 ms measured in Aug 2020 to τ = ~ 3 ms in the West cryostat and ~ 4.5 ms in the East cryostat by Summer 2021 and remained at these levels through 2022.…”

“…Each of the LAr-TPC detectors, namely MicroBooNE, SBN's Far Detector (SBN-FD, also known as ICARUS-T600) and SBN's Near Detector (SBN-ND) is essentially a cryostat filled with high purity liquid argon and equipped with an electronic readout that measures the ionization charge produced by the passage of charged particles. The MicroBooNE has been operational 2015 -2022; the SBN-FD Icarus detector has been operational since Feb 2020 (Geynisman et al, 2021); and SBN-ND detector is projected for start of operations in 2023 (Geynisman et al, 2017). The original ICARUS-T600 LAr-TPC was installed at the INFN Gran Sasso Underground Laboratory (LNGS), Italy, where it was operated from 2010 to 2013 taking data on the CERN to Gran Sasso neutrino beam.…”