External Cryo-Cooler

The Equinox GPU includes an LN2 fill port but no means of automated cooling. For brief sessions, manual filling from a dewar is adequate — pour LN2 into the port, wait for it to boil off, refill. But sustained compute workloads require sustained cooling, and a human with a dewar is neither a reliable nor a dignified cooling solution. The External Cryo Cooler provides continuous, automated LN2 delivery to one or two Equinox GPUs for up to eight hours from a single fill.

The system is a closed loop. LN2 flows from the 2-litre dewar through a vacuum-insulated transfer line to the GPU's cold plate, absorbs heat from the YBCO superconducting VRM and the die, returns as cold nitrogen gas through a second vacuum-insulated line, and re-enters the dewar where it re-condenses against the remaining LN2 inventory. The loop is driven by a magnetically levitated centrifugal pump — the same zero-contact bearing technology used in turbomolecular vacuum pumps. The magnetic levitation eliminates mechanical bearings, which would transmit vibration to the LN2 column and from there to the GPU cold plate, potentially creating microphonic noise in the solder joints.

The flow rate is adjustable from 50 to 400 mL/min. Higher flow rates provide more aggressive cooling and tighter temperature stability (±0.3K vs. ±0.8K at low flow), but consume LN2 faster because the higher flow rate increases heat ingress through the transfer lines. For a single Equinox GPU at full load (450W GPU + VRM dissipation), the optimal flow rate is approximately 200 mL/min, which provides ±0.5K stability and 8 hours of autonomy from a full dewar. For dual GPU configurations, the flow rate must be increased to 350 mL/min, reducing autonomy to approximately 4 hours.

The dewar is vacuum-insulated with a calculated boil-off rate of 0.3% per hour when idle — meaning that a full dewar left unpowered will retain 93% of its LN2 inventory after 24 hours. The top-mounted fill port accepts standard dewar nozzles and can be used during operation without shutting down the pump. The 2.4-inch LCD displays temperature at the GPU cold plate, flow rate, current LN2 level (by weight sensor), and estimated time remaining at current consumption rate. An audible alarm sounds when the dewar reaches 10% capacity, and the pump shuts down automatically at 5% to prevent dry running.

The quick-disconnect fittings are rated for cryogenic service to 77K and can be connected or disconnected without tools. Each fitting includes a check valve that prevents LN2 from spilling when disconnected. The transfer lines are 1 metre long and flexible enough to route through a standard desktop case without sharp bends that would restrict flow.