Superconductor rotating machines usually need to operate in a temperature range of 15-60K (-258 to -213ºC), which rules out liquid nitrogen as a coolant having a minimum workable temperature of 64K.
The alternative for rotating machines is therefore to used a (pressurized) cold gaseous helium flow, or to sub-merge the rotor into a bath of liquid neon with a boiling temperature of 27K.
Both are noble gases with (relative) easy handling and limited safety hazards.
However, GHe has a lower thermal capacity compared with a cryogenic liquid, so therefore its capability to remove heat is. Solution is to work with a pressurized systems to create sufficient mass flow, normally at a pressure of 10 to 20 barg.
To circulate the helium gas, Stirling CryoFans are used. These can be integrated in the Stirling Cryonics two-stage Cryogenerators, creating a system set-up that can remotely cool applications down to 18K.
Two-stage Cryogenerators have two cooling loops, one at 80K and one at 20K and both have their individual CryoFan in an independent loop. The 80K loop can be used to shield the 20K loop or as pre-cooling, therefore reducing the thermal losses for the 20K loop.
The heat load represents customers application (magnet, generator, motor, chamber etc.). Light blue Q1 is the thermal load on the 80K loop, darker blue the thermal load on the 20K loop.
The system control operates and safeguards the Cryogenerator and controls the fan(s). The speed of the CryoFan is fully adjustable to control the flow of helium gas in the closed loop adjusting to customers requirement (gas flow, delta T).
Stirling Cryogenics can design and offer a customized system for your specific project, please contact us to discuss your requirements.