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October 21, (Friday)
Martino arrives at the telescope in the evening. Alessandro, in remote, has been optimizing the way to put some pressure in the mixture circuit in order to reach the (local) atmospheric pressure, ie about 720mbar. The solution he proposes, switching of one of the two PT compressor, works very well. Bravo! We also have to get a bit of mixture back in the reserve, roughly 70mbar, otherwise the pressure increases above the desired value. Martino mounts the accelerometer on the NIKA2 'nose', but the reading doesn't seem sensitive enough to show clearly the PT induced vibrations -> solution for the moment not implemented! In the meantime, Alessandro restarts the second compressor to leave the system in precool mode overnight. So tomorrow the cryostat will be nicely cold at ~5K.
October 22, (Saturday)
Yesterday evening at 23 the telescope has been stopped due to the wind. This leaves us more freedom to play in the cabin. So we (= Martino in the cabin and Alessandro remotely connected, taking care of the cryostat and sharing the responsability..) begin the realignement process, the basically implies:
* Increase the pressure in the precool circuit to be able to move the PT head. This is achieved switching off one PT compressor.
* Move the head (one at a time), feel where it starts to touch to the NIKA2 4K, and find the ideal 'central position'.
* Holding it in this position, screw the dumping screws until the touch and tighten them a little.
* Restart the PT compressor, go back in the precool phase and when it's time launch the condensation
* During condensation, optimize the PT2 position by playing (gently!) with the screws and looking for a max in the 4K plate temperature. NOTE: typically starting from the ideal position, turning the screw by 45° in any direction is enough to start touching. So it's a very delicate process!!
* When the condensation is finished and the system is cold, check on the Camadia time traces that the noise is ok.
To give an idea of timing, today we did:
7h45 Switch off 1 PT compressor 8h40 P in the 'gaines' is ok, start to play around with PT head position 9h45 PT position adjusted, restart the standard cooldown by switching back on the second PT compressor. 12h00 Launch condensation. NOTE that we could do this very soon because the system had been already well precooled before starting the whole PT adjustement process. If it's not the case, wait for the correct temperatures beafore launching the condensation! 20h00 Tbm at ~200mK, good enough to see how things are going and if the PT lines have disappeared (but not ok for detailed tests as T is not yet stable enough)
October 23, (Sunday)
The noise traces seem to indicate that the issue has been solved. Playing around with the tone powers and with camadia to get a feeling of its current configuration. It seems to be pretty stable, very well! Still, too soon to give definitive answer: we'll have to see what goes on when the telescope moves (it's still stopped do to the wind, constantly very high!), and especially when we go on sky.
October 24, (Monday)
Still windy! It's now more then 48hrs of continuous 'wind stop'. Tonight the gusts reached 200km/h.. This morning wind, rain and hail. The gusts were still too strong and the transport has been canceled: Juan M-P, that was coming up with it, had to go back to Granada and will arrive tomorrow with the rest of the NIKA2 crew. Hopefully the weather will improve. It should, but the tuesday to wednesday night might still be affected by the wind. Let's hope not..