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Further decisions about next interventions etc.
New developments and decisions, including minutes of re-commissioning meetings after the 2025/03 re-commissioning campaign
Minutes of the 20250411 meeting
Partecipants: Stefano, Alessandro, Samuel, Nicolas, Xavier, Carsten, Miguel, Dave, Angel, Stergios, Monica, Juan, Albrecht, ...
The next intervention, aimed at changing the Ar2 Box C cold amplifier, will be on 3-4 June 2025. All agree to fix these dates. The change will happen on June 3rd (Tuesday, 8 a.m. to 8 p.m., during extended maintenance. The team will stay at the telesscope until the next day, to be ready in case something needs to be done also on June 4th. Amplifiers ptions are in hand.
It is discussed if a change of Ar3 could be foreseen (Box S, i.e. line 7, is currently noisier). There is another Ar3 available, actually better performing, but line 7 is completely dead. The one installed was originally labeled as "spare". There exist yet a third, with all lines working, built on a different mask, but it seems to be more sebsitive to magnetic fields, therefore was excluded fom NIKA2. Ar3 shall not be changed in the June intervention.
Samuel suggests that the amplifier of Ar3 Box S, in case the enhanced noise of this box is due to the amplifiers and not to the array. Stefano will check if also before the upgrade the Box S was noisier than the rest of Ar3. If so, then the main suspect would be the aplifier. If not, then more likely the array.
Alessandro discussed with Xavier in the past days. As a matter of fact there is always one 1,2 mm array dominating the sensitivity. In the current case it is Ar1. The other array (Ar3) gives a small contrinution. For example if the NEFD of Ar1,3 are 15 and 20, then the Ar1+3 result is 12.5 (if pure Gaussian noise). Alessandro proposes that it could be scientifically more interesting to have a third band in place of the Ar3. It must be at high frequencies, because of the dichroic. Possibilities are a 350 GHz band (unique in the World, but with difficulties in weather conditions, primary, and not clear if compatible with the current corrugated lenses) and a 220 GHz band (zero level of the SZ effect, AM: or in any case it would be a "1.5mm array" much less sensitive to atmosphere so better in average taus). Very tempting. This possibility will be discussed further in the future months. Carsten notes, that if we want to go into the submm, a formal proposal must be developed, putting all pros and the cons on the table. At the moment, it goes far beyond the aim of the next intervention.
Possible change of position of Ar3 (or Ar1+2), to put all three arrays to the same focus. The difference of focus before the upgrade was 0.3mm between Ar1 and Ar3, but Ar2 was in between them, therefore focusing on Ar2 was a good compromise. Now (after the upgrade), Ar1+3 have basically the same focus and Ar3 is displaced by 3 mm. We need more data to assess if we really want to change the position of the arrays. Therefore such an intervention is excluded from the June 3rd work. We may add another offset to the focus corrections input by observers.
This means that a possible change of position of the arrays will be shifted to next year. September/October 2025 are excluded because they're too close to the IRAM 30m School and to the next Summer/Winter pool weeks. This one year time can be a nice asset to evaluate and propose more "formally" the possible introduction of a 3rd band.
The commissioning, the week of 17-June is discussed. Stefano may not be available, but IRAM/Granada astronomer are in principle available. A couple of days are needed. The telescope will be stopped for heavy maintenance for the last week of June and the first week of July.
After the meeting: Stefano checks the noise plots of beam-maps of Ar3, before and after the upgrade. In the following figures, you see on the left the noise of Ar3 boxes in the NIKA2 Run 68 (before the upgrade) and on the right Run 72 (after). The increased noise of Box S is clear in Run 72 (rp nr between ~800 and ~900), but I do not see in in Run 68. Note the much lower noise level of the new Ar3.
After the meeting: Alessandro found the evaluation amplifier he got from TTI Norte in 2014 before ordering the big bunch. Can be in principle used for NIKA2 to replace the box S one. Apart from that I only have one more of these 2-3GHz amplifiers from TTI Norte that I had bought for another project on independent funds. Since that other project is finished since a long time this additional amplifier can be given to NIKA2 as spare. But somewhere at IRAM (could be in Grenoble ?) we should have four more such amplifiers. I remember that it was actually IRAM that ordered the amplis to TTI on internal funding. In any case we have two and they are in the box already, we'll bring them to Pico Veleta.
