cold cathode gauge reading wrong? Pretty sure that's not the case. With IVC valves closed, it pumps down normally. And we choked the Turbo pump last time trying to pump it out - the pressure is definitely high.
failed again at lower seal? Seems pretty unlikely. Usually if that seal fails, we see it at 77K
is the stripline elbow leak worse? Could it be that when the top of the fridge gets cold enough, this starts leaking badly? I think this can be ruled out:
leak is still present long after transfer, when top of fridge is warm but IVC still cold
leak disappears when IVC gets warm enough (MC somewhere between 12 and 150 K)
this suggests that the leak is somewhere inside the main bath
so most likely candidate: one of the semi-permanent IVC indium seals has sprung a leak, than only occurs around 4K.
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