Sub-Kelvin cooling technology is a critical prerequisite for high-sensitivity detection in deep space exploration and quantum computing. Operating identical sorption coolers in parallel is a common engineering approach to enhance cooling capacity and extend hold time for these cryogenic platforms. However, this study reports an unexpected “symmetry breaking” phenomenon observed in a parallel Helium-4 sorption cooling system where the cold heads are connected via Oxygen-Free High Thermal Conductivity (OFHC) copper linkages. Instead of the expected uniform load sharing, the system spontaneously evolves into an asymmetric “quasi-series” operational mode. In this state, one cooler preferentially consumes its liquid helium inventory while the other remains dormant, significantly reducing system efficiency. To elucidate the underlying physics, a transient thermal-fluidic resistance network model was developed and validated against experimental data obtained from a dual-cooler test rig pre-cooled by a G-M cryocooler. Theoretical analysis reveals that this thermal locking originates from a positive feedback loop driven by the temperature-dependent thermal conductivity of the copper straps. Experimental results further demonstrate that system stability degrades significantly with increasing thermal load, with the synchronization ratio dropping from 75.3% at 0 mW to 51.3% at 3 mW. This indicates that at higher temperatures, the destabilizing gain of the thermal link overwhelms the restoring stiffness of the sorption mechanism. To address this intrinsic instability, a passive suppression strategy using a series “Ballast Thermal Resistance” is proposed. Numerical optimization identifies a critical resistance value of approximately 10 K/W, which effectively dampens the positive feedback and restores the synchronization ratio to over 95% with a negligible thermal penalty of less than 20 mK. These findings provide a theoretical basis and practical design guidelines for the stabilization of multi-cooler cryogenic networks.
Lu et al. (Thu,) studied this question.