The Cryogenic System
The superconducting coils must be held at cryogenic temperature; the cooling plant is a continuous load the machine's power balance must carry.
Keeping the magnets cold
Even high-temperature superconductors run far below room temperature. The burner's REBCO coils operate at cryogenic conditions, cooled by a closed helium (and/or nitrogen) refrigeration plant. The cryostat isolates the coils from room-temperature surroundings with vacuum and multilayer insulation so the heat leak the refrigerator must remove stays small.
Heat loads to remove
- Static heat leak through supports and radiation into the cryostat
- Nuclear heating from the 5.44% neutron flux reaching the coils
- AC and joint losses during field changes
- Any local heating that threatens the temperature headroom
A recirculating-power item
The refrigeration plant runs continuously and draws electrical power, so it is part of the recirculating-power budget alongside heating and pumping. REBCO's larger temperature headroom helps here: it tolerates more heat before quench, which relaxes the cryogenic duty compared with low-temperature superconductors and improves robustness against transient heating.
The cryogenic design is tightly coupled to shielding (which limits nuclear heating of the coils) and to quench protection (which must act before a warming coil is damaged). In the design study the cryogenic loads are sized from the modeled heat leaks and neutron heating; they are a real, accounted-for parasitic load rather than an afterthought.
Redundant refrigeration capacity is part of the availability design, since losing cooling would eventually warm the coils toward their limit. On a multi-unit site the cryogenic plant is one of the systems that can be shared or backed up across units.