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September 20, (Tuesday)

At 3h the cryostat is pumped from the air trapped. According to the pressure iinside the big pipe 60-meters, we estimte that the volume of the pipe is half that of the reserve (17 mbars in the pipe correspond to 8 mbar in the reserve.

* At 3h15 starting the real cooldown. LEt's hope this time. Later this morning we should add 3He.

Spent the whole day cleaning the mixture. Used the LN2 trap from NIKA2 mounted in series in the injection. A series of technical limitations made that the procedure has been slow. The final step was a preref in which the mixture circulated 1 hour below 70K (4K injection PT). From the original 606mbar we have now 484mbars. So we have lost around 120mbars, or 1/5 of the reserve. Could have been worse considering the nature of the problem we had. Tomorrow I'll add some mixture out of the Néel group stock and try to start the real cooldown.

Bad day: the 3He pump exploded (part of the chamber broke violently opening to air a sealed section and letting leak all its oil), most probably caused by an overpressure due to a blocked oil filter. We don't know how much 3He we lost, we're working hard to try to clean the He gas and circuitry from possible air contamination. At best the cool down of the cryostat is delayed by few days. At worst the run is cancelled.

Finish mounting NIKA2 back in place. Everything went fine and smoothly, without problem.
Start leak tests.
Zemax simulations done. Ray tracing figures look scary, but it's the PSF that matters:
- For the defect on the 1K lens: ~1/3 of the image surface is affected (top side); extra aberrations appear in the side lobes at ~10^-2 level, the beam peak decreases by up to 6%, the encircled energy at the 1st dark ring (-13dB level of Gaussian fit) decreases by up to 5% <=> the benefit of the corrugations AR effect is cancelled out for those pixels. It seems acceptable since most of the image is not or negligibly affected; we'll see on the sky with beam maps.
- For the defect on the 2 100mK lenses: 80% of the image is affected (red cross shape); extra aberrations appear in the side lobes at ~5x10^-3 level, the beam peak decreases by up to 4.5%, the encircled energy at the 1st dark ring (-13dB level of Gaussian fit) decreases by ~3.7% <=> a significant fraction of the benefit of the corrugations AR effect is cancelled out, but not all. It seems acceptable.

Arrival at the telescope of Samuel.
Unload truck dismount NIKA2 nose, roll NIKA2 body it in the corridor.
Dismount NIKA2 body, up to the cold stage optics.
Change the 1K lens in the corridor: remove the smooth one, place the corrugated one. See a small defect that hadn't been seen before on a section of the new corrugated lens: groove ~5mm wide, ~0.1-0.3mm deep, ~5-7cm long. Probably acceptable; decide to keep the lens, Samuel will simulate the effect with Zemax.
Change the 100mK lenses in the servo room (floor below the receiver cabin). Here also a small known defect on 2 of the 5 lenses: ridge ~0.5mm wide, ~0.3mm high, along 2 perpendicular diameters. Before coming Samuel estimated with a simplified simulation it was acceptable, he will simulate more accurately the defect.
Change the 2mm array: replace the 1020 KIDs array with the new 616 KIDs array.
Change the dichroic.
Start mounting again everything together.

Arrival at the telescope of Johannes, then Alessandro, Martino and Aurelien with the truck.