Problem(s) Encountered:

CCD temperature was high (> -50C) during night. (cf. outside T~4C, RH 20~30%)  At ~2:20am, CCD temp. reached 0C.
LN2 filled at ~3am. however, CCD did not cooled below -50C until morning.

Solution:

Firstly, it is worth noting that if a detector warms up to an abnormal temperature, MDM staff should be consulted before cooling it back down again.  Thankfully in this case, nothing bad happened, but cooling like this can lead to issues such as ice forming on the chip.

This problem was a pain to diagnose but it ultimately appears that the screw holes for the collar where LN2 is added were weakened and not allowing a full seal which ultimately led to a persistent LN2 leak.  I’ve changed out the fill cap/collar and implemented a new approach to removing this (as needed for certain instrument configurations).  So far so good...