Design and construction of a cryogenic subcooler-box for supplying single phase supercritical helium to dark matter and gravitational wave experiments

TL;DR

This work documents the design, fabrication, and integration of the ALPS Cryo-Platform Subcooler Box (ACPS) at DESY to subcool and distribute supercritical helium under high heat loads for dark matter and gravitational-wave experiments. It details the interfacing with the 1.6-km HERA transfer line, the JT-valve–PHEX–subcooler bath cooling loop, and the 40–80 K thermal shield, supported by instrumentation and safety systems. The paper presents heat-load–driven mass-flow calculations for 4.5–5 K and 40–80 K circuits, outlines FAT/SAT validation, and describes the installation and interface with existing cryogenic infrastructure, along with a plan to reconnect to the DESY Cryo Plant. The ACPS is demonstrated to provide independent, controlled cooling across three transfer lines for multiple experiments, positioning the DESY cryogenic platform to host future high-precision measurements in particle physics and astrophysics.

Abstract

We report on the design, development, and installation of the ALPS Cryo-Platform Subcooler Box (ACPS), which is part of the cryogenic platform being established in the HERA North Hall at DESY to supply helium for cooling large-scale dark-matter and gravitational-wave experiments with very high heat loads. The ACPS is capable of subcooling supercritical helium supplied via the 1.6-km-long HERA transfer line by means of a pipe heat exchanger immersed in a subcooler bath filled with liquid helium produced through Joule-Thomson valves. It is also equipped with numerous cryogenic components, including control valves, flow meters, and safety valves, enabling experimental operation to be carried out directly by the ACPS itself and thereby reducing the cryogenic requirements imposed on the experiments. To support a wide range of experiments, the ACPS provides three transfer lines that deliver different levels of cooling power.

Figures (6)

• Figure 1: Schematic view illustrates the CB42 refrigerator supplying helium to FLASH, AMTF and CMTB (which are test facilities of the XFEL project) at the DESY campus, as well as the HERA TL in the HERA tunnel. At a distance of 1.6 km along the HERA TL, the ALPS subcooler NR and the 200-meter-long dipole magnet string, parts of the ALPS experiment, are connected. Beyond that, the HNH area is located, housing the HERA Box (old), the H1 Box (old), and the newly introduced ACPS with three TL ports designated to three experiments (Exp. 1, 2, and 3). Additionally, the H1 Box includes an option for adding an additional experiment, called Exp. 4, due to its two outlets (as one is used only for the ACPS). The schematic also highlights the warm gas connections.
• Figure 2: An enlarged view of the gray shaded area in Fig. \ref{['fig_ACPS_H1_HB_flow_scheme']} (which shows the complete flow scheme of various cryogenic lines and systems in the HNH area) depicts only the inlet TL originating from the H1 Box side, along with a subcooler bath featuring an integrated PHEX and a heater (HC). Additionally, it shows various cryogenic valves (VC), hand valves (VH), safety valves (VS), pressure transmitters (TP), Cernox temperature sensors (TTC), platinum thermometers (TTP), and a flowmeter (TF) for TL1 to Exp. 1. The transfer lines for TL2 to Exp. 2 and TL3 to Exp. 4 are highlighted in Fig. \ref{['fig_ACPS_H1_HB_flow_scheme']} in Appendix B.
• Figure 3: 4.5-5K circuit diagram of various TLs, distribution boxes, and experiments operated in the temperature range of 4.5 K to 6 K highlighting the heat loads given in Tab. \ref{['tab:heat_loads_sources_4K_table']}
• Figure 4: 40-80K shield circuit diagram of various TLs, distribution boxes, and experiments operated in the temperature range of 40 K to 80 K highlighting the heat loads given in Tab. \ref{['tab:heat_loads_sources_40K_table']}
• Figure 5: ACPS photograph showing its current status.