as I was yesterday, it’s time to stand on the porch and curse the Seebeck effect, which is the phenomenon behind thermoelectric currents. If you take two different conductors and make them touch each other, you get
cooties a current if there is a temperature gradient present in the system. You can run this in the other direction and create a temperature difference, which is why thermoelectric coolers/heaters work; this is the Peltier effect and is the technology in most portable active coolers (if it plugs in and doesn’t have a compressor, then it’s probably a Peltier cooler).
Now, imagine you have a vacuum system running an experiment which is very sensitive to magnetic fields. Because you are trapping atoms, you have MOT coils dissipating a few Watts of power (while the trap is on) and you are heating your alkali metal reservoir to facilitate their introduction into the vacuum system. You will have a temperature gradient along your nicely conductive vacuum system. So if you have some dissimilar metals touching the vacuum system, somewhere, you’ll get a tiny amount of current flowing through it, creating a tiny magnetic field. But since such magnetic fields are phenomena non grata, having a thermoelectic connection — which you did not expect to have — is a bit of a pain.
Found it though. Something was inappropriately touching the vacuum system, so we had it arrested and now we make sure there’s a few mils of kapton between it and the vacuum chamber.