Earlier this week, we said that the MIRI instrument on JWST was in the process of cooling down to less than 7 Kelvin. That has now occurred, and the instrument passed its critical “pinch point” safely. As the instrument cooled, its ability to get cooler improves, except at a range of around 15 Kelvin. The risk with this cryocooler operation was that, if there was more heat than initially modeled, the cryocooler would have not been able to reject all the heat and actually made the instrument warmer.

The cooler is performing better than the engineers expected. This helps get down to the 6.4 Kelvin needed to suppress the thermal energy of the atoms in the detectors themselves, called “dark current”, which is bad because it imitates a real signal. Once the instrument was cooled down, engineers checked out the detectors and confirmed that they were healthy.

More Information

NASA press release

Webb’s Mid-Infrared Instrument Cooldown Continues (NASA)