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September 22, (Thursday)

T0+48h. T_mixing_chamber=162K; T_still=82K. T_4K_plate=27K. (was in run 1 at T0+48h: T_mixing_chamber=202K; T_still=104K. T_4K_plate=60K). This is explained by the fact that we started cooling down after the mixture washing, when the cryostat was already a bit cold.

AB has submitted 3He via DHL to Granada.
SN has contacted Linde-US to get green-light to order 20l 3He as spare for the future.
T0+36h. T_mixing_chamber=205K; T_still=124K. T_4K_plate=62K. (was in run 1 at T0+48h. T_mixing_chamber=202K; T_still=104K. T_4K_plate=60K). This is explained by the fact that we started cooling down after the mixture washing, when the cryostat was already a bit cold.

At 3h the cryostat is pumped from the air trapped. According to the pressure inside 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.
Olivier arrived at the telescope. He started to work on the electronics and assemble the crates.
Another bad new: the Néel 3He stock bottle is empty! Alessandro got in contact with Alain in order to ship some 3He supply from Grenoble ASAP. In the meantime we put a bit more 4He in the mixture (from a high pressure bottle gas we had in stock) in order to continue the cool down. Cooling down to 1K is the longest part, until then the 3He is not absolutely necessary, so hopefully the 3He will arrive just when we need it.
IRAM Granada started the process to order soon some 3He supply, 2 pumps (replacement of the broken one + a spare), and oil filters.
The whole electronics is mounted and ready to be tested.
After another small accident the amount of mixture is 454mbar. Added 87mbars of 4He, waiting for the 3He. So the total amount in P3 should now be, temporarily, around 540mbars. Plan to add 40mbars in 3He. The volume of the reserve is 135 liters (measured today, we had always thought it was 100 liters). So it means around 5 liters of 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.
In the meantime Martino continued working on the Turbo pump problem, and found its cause: the cable inside the Automate box which transfer the informations in and out of the pump controller, was in fact made from 2 cables soldered together, at the soldering junction some insulation layer was missing around the various wires contained in the cables, causing 3 of them to be in contact with each other. One is a ground, which must have entered in contact with the others while working on the MPPSYNC. Isolating the wires allowed to recover the control of the pump (and fix an old patch in the LabView program that had been necessary to write for a proper communication without knowing that it was the short cut between 2 wires that made it necessary).
Martino and Johannes left with the CNRS truck in the afternoon.

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.
Before this big event, Martino and Alessandro were working on the communication problem with the 3He turbo pump. Martino found a way to communicate directly with the pump to switch it on and off, but impossible to change the speed. He was continuing investigating the problem, when the 3He pump exploded.

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.
Fix a communication problem with the MPPSYNC instruments inside the Automat box (above NIKA2 on the side wall). But then the 3He turbo pump (side wall above NIKA2, below Automat) is not responding any more to any command.

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.