Related to Are there any promising next-generation space station cooling technologies?, I'm wondering specifically about a technology that hasn't been mentioned there: Zeeman slowers. Since these are a) used to cool atom beams from at least 290 K to 5-10 K (if not lower) and b) operate without convection or conduction by triggering increased thermal radiation from cooled atoms, it seems that they would be not only suitable for general-purpose cooling in space, but if anything, a good deal more efficient there compared to expansion-compression cooling systems than on Earth, since they skip the whole "pumping heat to enormous radiators" step. And they've been in use for something like three decades in lab setups. What am I missing?
To carry the answer from the other thread over here as well:
No, Zeeman slowers cannot be used as space station coolers
The reason is that the heat flow they provide is in the nanoWatt range.
So no, they are not "close" to being used as general cooling systems in space, for the same reason that placing a home-made water wheel under your kitchen faucet is not "close" to providing you free energy for your home. Sure, you might get a LED to shine faintly but that's about it.
EDIT: Question was asked "Why can't this be scaled up"?
Because there are very narrow tolerances regarding velocity (speed and direction) as the atoms enter the tube. If you have a low density beam then this is fairly easy to maintain, because the atoms are not interacting. But once you scale it up to have a mass flow that is significant enough to provide the amount of cooling that is needed, then we no longer have a particle beam of atoms but a flow of gas or liquid. This means the atoms are bumping into each other and Browninan motion destroys any chance of meeting the narrow tolerances regarding the entry velocity.
Too cool down the station, we must transport energy away from the station. Period. That can be done through radiation, or by letting some substance boil of.
The Zeeman slower does neither of that, and is then strictly not usable for "general cooling". In fact, it produces more heat as it uses electricity.
Changing what parts of the spacecraft are hot or not might still have an effect. For instance, if the radiators are hotter, they radiate more energy. The Zeeman slower only makes the surroundings a little hotter, so traditional expansion-compression systems do that part a lot more efficient. The main advantage of the Zeeman slower is to cool a tiny amount of atoms to a really low temperature (just a few Kelvin), so it can be used to cool components that needs to stay really cool. (like super conductors or space-telescope optics). Note that the output of cool atoms from the beam is very small, so any components cooled by it have to be extremely well thermally isolated.