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Plan for the NIKA2 re-commissioning (March 18th to 25th + March 30th to April 1st, 2025)

See also the minutes of the 2025/01/24 meeting dedicated to the re-commissioning (at the difference of the minutes, which describe things as they were discussed during the meeting, the test plan below, originally extracted from these minutes, may contain few differences resulting from upgrades depending on possible evolution of the hardware situation and new information since the meeting. So please refer to this test run page for the actual plan that the re-commissioning team will follow (in principle differences should be marginal).

Originally, two weeks were booked for the re-commissioning. The plan was to quickly assess the relative focus between the three arrays and decide if we need to re-open in order to move the arrays and bring them to the same focus position (as much as possible).

The re-commissioning has now been reduced to one week in march and a second week at a later time, possibly at the end of May or beginning of June. In fact we realised that warming up takes 5 days, cooling down takes ~one week, and therefore re-opening the cryostat to move the arrays would occupy more than one week and we would have had no time for the second part of the re-commissioning (after the 2nd opening).

Participants

(preliminary)

On site: Angel (AoD), Stefano, Carsten, Mónica,

Remotely: Nicolas (except 18/3 @ 17 and 21/3 in the evening), Xavier (20-24/3), Samuel, Alessia (18-21/3), Juan Macias-Perez

Brisa is warned of the chance of using EMIR if anything goes wrong with NIKA2

Overall schedule

• March 4th - 11th: NIKA2 hardware upgrade
• March 11th - 17th: NIKA2 cooling down (maybe start already on the 9th, see above)
• March 18th: start the re-commissioning of NIKA2, after cooling down

• We are going to use the use t22 account
  -> copy the current scripts into the directory PaKo/202503/

• IMPORTANT NOTE: if problems pop up during the recommissioning?
  -> re-open! (hardware people be ready)
  -> use EMIR meanwhile

• March 18: the first action is the new sweep (Martino, Alessandro, Dave)
• The second action is checking the radio alignment using the Eccosorb technic (added by SL, 30/01/2025). The following assumes radio alignment is correct (if not, either it can be compensated, or a re-opening is necessary, which means few hours to many days delay).
• We then spend one-two days for the first characterization of the arrays, aimed at determining the new kidpars (IDL pipeline). Nicolas will work with us remotely during these first phase. Details are given below.
• This process will take ~2 days, including the new kidpars/DAFs and likely also the verification of the relative focus between the arrays. It might be faster, but let's count ~2 days.

• At this stage we planned to know if we need/want to re-open the cryostat to adjust the relative position of the arrays (along the z axis). We have decided to post-pone this decision to a later time, after a thorough analysis of the data taken during this first re-commissioning week. Two cases might apply:
  

  1. The re-opening will happen (very likely). We had originally scheduled it for March 30th (Sunday), but eventually decided it was safer in terms of people travel organization to reach this stage of knowledge of the upgraded instrument situation before taking decision (reverse everything / just move arrays / no re-opening necessary: go to B.). The following assumes we don't need to reverse everything.
     For the rest of the March 18-25th week, we proceed with the first part of the re-commissioning, aimed at characterizing the new arrays and test/characterize as much as possible the upgraded NIKA2
     On March 25th (Tuesday, maintenance day) @ 10:30: start warming up NIKA2 Only if necessary (depends on the decision mentioned just above)
     On March 30th (Sunday) continue got get more re-commissioning data, possibly at the light of the processing of the preceding week data.
     At the date decided above, probably sometimes in April or early May: the 2nd hardware intervention will begin and will take 2 days. The arrays will be moved along the z-axis in order to bring them to the same focus (as much as possible)
     The 2nd half of the re-commissioning (after the 2nd intervention) will be at the end of May or beginning of June, because April is fully taken by EHT and in the first half of May not everyone will be available.
     

  2. we decide not to re-open (unlikely).
     We proceed with as many re-commissioning operations as possible, including the full characterization of the instrument, as described in the next Section below, including stage-2 operations such as a pointing session and de-focused beam-maps.

Detailed operations

1. new sweep, closed window.
   This will show already if any KID has enhanced noise.
   (no info about the dichroic performance)

2. radio alignment.
   

   • Preliminary to the radio alignment the team who will have done the upgrade operation during the preceding week will have finished its shift by checking the optical alignment with elevation axis lasers and checked the position of the laser spot on the entrance widow (should be at center +- 3 mm, M5 & M6 back rings are used to adjust the laser spot position).
     

   • The radio alignment consists at checking that the internal optics of the cryostat is well aligned with the telescope optics; which means not only that the optical axis of the whole system ends up at the center of the arrays so that without Nasmyth correction the image of the point source is at the center of the arrays, but more importantly that the pupils are well aligned so that the illumination of M1 from the cryostat optics is well centered, otherwise we would pickup some warm spillover from the background behind the telescope, degrading the signal to noise (sensitivity) and the beam shape quality.
     

   • The NIKA2 optics has been designed such that there's 3 pupil surfaces in the system: M1 itself, a surface as close as possible from the entrance window (in practice it is few cm behind it), and the cold pupil surface at 100 mK where we place the cold stop that blocks the warm spill-over ring from the M1 edge, so that the only light that reach the arrays come from a 27.5 m diameter inner disk centered on M1 at few 10s cm margins depending on the fields. When the radio axis is misaligned these inner disks are not inscribed anymore in M1 and spill beyond its edge.
     

   • To check the correct alignment of the pupils we need to have the traces of a representative number of pixels (KID) looking at a cold stable sky (correct opacity tau < 0.3, and good stability that can be checked with the gray diagrams in the right part of the acquisition tones window; for each array the maximums of the 2 diagrams must be relatively closed to each other). Then we use a piece of an Eccosorb foam that we slide from the outer of the window toward the center ; we note the position from which the KIDs traces react to the warm signal from the Eccosorb. We repeat the operation from 4 opposite and perpendicular directions (left - right - up - down). The distances from window edge to position where the warm pick-up happens, allow determining how well the cold stop is aligned with the entrance window, and thus how well the pupils are aligned.
     

   • If the misalignment is < 5 mm, we are fine, it may be useful to re-adjust the optical alignment with the radio one : iterating laser and Eccosorb operations. If the misalignment is > 10 mm, we need to warm up and adjust the internal optics alignment. To do that remove the cryostat nose cap, and adjust the long tie rods that control the inclination of the M7-M8 optics block with respect to the cold optics (lenses) block. Ask experts like Martino & Alessandro for this operation. If the misalignment is > 5 mm and < 10 mm, we are in the "gray zone", let's talk.
     

   • For more details on the optical and radio alignments with NIKA2 check the following link: History of optical and_radio alignments of NIKA2; this document (which is also available from the NIKA2 wiki main page) contains drawings that help understanding the procedure.

3. check DAQ on sky, check traces:
   we could again already see if there are problems with some KIDs
   noise properties
   also shows if the dichroic is healthy
   check source and beam width
   

4. pointing, focus, pointing, beam-map
   This very first observations might be a bit tricky, because we likely do not have the possibility to alternate the new sweep to the old sweep (because we have completely new arrays). Nicolas will intervene and use the IDL pipeline to determine the first kidpars.
   We have new arrays, therefore:

   • first guess of kidpars from Martino's design
   • a full beam map would take 30 min and the data red of a full beam map, take roughly the same time
   • Therefore we decide to take a smaller beam map, on the central kids only
   • check the source on the TOI, if it's here, then proceed
   • process the small beam map
   • if on focus, determine kidpars for central KIDs, otherwise refocus and repeat
   • the smaller beam-map saves 1-2 hours over the whole procedure

   • the reference (central) pixel shall be determined!

   • when on focus and the central kidpars are there, proceed
   • full beam maps
   • full kidpars
5. produce also PIIC preliminary RPPs (Stefano)
6. This might take up to ~2 days. Hopefully faster, but let's keep some margin.
7. any possible idle times could be filled by EMIR or with the PIMP

8. I insert the PIMP operations here, but they could be performed also later, in case there's no occasion at this point:
   The Goal is to determine / check the passbands with the PIMP
   

   • Who on site is able to run the PIMP?
     

   • Samuel will be available online to instruct Stefano or others at the telescope on how to use it.
     

   • Moreover the online documentation will help (see the NIKA2 Wiki)
     

   • The PIMP needs a special .ini file for the DAQ
     

   • The PIMP will be craned up to the cabin in advance (either during the Holography week, or during the NIKA2 hardware intervention)
     

   • Analyse the PIMP data: Juan (in collab with somebody from IRAM to do knowledge transfer ?)
9. Once the full beam maps and kidpars/DAFs will be ready and analysed, we will assess the "flat field", i.e. we assess if the current shadowing caused by the old dichroic is gone. We can also assess how big is the difference in beam shape/s (i.e. focus) across the f.o.v.
10. with the focus maps + beam maps, we assess immediately how much is the focus difference between Arrays 1,2,3. few scans are in principle enough, but we'll need some statistics, in order to be more conclusive and determine the offset with high enough precision. These scans can be part of the initial 2 days, or might some more time, depending on how long it takes us to complete the kidpars/DAFs.

11. At this point, we can assess the focus situation and have a first impression about the need to re-open NIKA2. Nevertheless, the final decision will be taken at a later time, after a thorough analysis of this week's data. Does the upgraded NIKA2 need to be opened again, so to optimize the (relative) position of the three arrays and bring them to the same focus?
    Are there any other issues that need to be solved by opening the cryostat?
    

    1. we see that that we likely will need/want to re-open the cryostat to adjust the relative position of the arrays and bring them to the same focus [and/or to solve any other issues].
       • assess by how much the arrays need to be moved (and which arrays) [Samuel, simulations vs. observations]
       • the re-opening was scheduled for March 30th, two days, but we decided to postpone it at a later time, after a thorough analysis of this week's data.
       • proceed with the re-commissioning for the remaining days, up to March 25th, and then also for the two extra days on march 30th to April 1st.
       • keep taking pointing, focus, calib_1scan, beam maps of calibrators
       • beam maps of Uranus in total power AND polarimetry mode ; polarized beam maps of QSOs, in particular on 3C286
       • perform the full characterization of the arrays and NEFD in total power. Preferred targets to do that:

         • 1h on HLS (bright source) ; older scans are available before any upgrade (telescope and NIKA2)
           

         • first assessment of new sensitivity ==> if good, then spend time on G2 (faint source)

         • deep integration on faint source G2 (5-10 hours) ; older scans are available before any upgrade (telescope and NIKA2)
         • Orion-B big maps with extended emission ; older scans are available before 30m painting and after painting (before NIKA upgrade)
         • M8182 big maps with empty sky, a bright compact source and a faint extended source ; older scans are available during new servo system upgrade, before 30m painting
       • perform the full characterization of NIKA2-Pol. If the external calibrator is confirmed to be working properly, use it too! Preferred targets:
         • polarimetry QSOs
         • polarimetry Crab Nebula
         • beam map on 3C286
         • beam map Uranus in pol-mode
         • If the external calibrator is confirmed to be working properly, take some scans with the external calibrator on and off. We need to characterize the zero level of the external calibrator. To this aim, short scans are sufficient.
       • Depending on the travel possibilities of the intervention team who will open again the cryostat and adjust the position of the arrays (Samuel, Alessandro, Martino...), the NIKA2 warming up will start sometimes between March 25th and April 1st.
       • The 2nd hardware intervention will happen sometimes in April/May depending on the travel possibilities of the intervention team, 2-4 days will be necessary. From March 30th to April 1st some additional commissioning data can be taken, depending on the processing analysis of the March 18-25 data, and decision on the warmup.
       • the 2nd part of the re-commissioning will take place either during the last week of May or during the first week of June

    2. we think that we will not need/want to re-open the cryostat.

       • proceed with the full re-commissioning on NIKA2 for the remaining days, up to March 25th, and then on the two extra days from March 30th to April 1st.
       • keep taking pointing, focus, calib_1scan, beam maps of calibrators
       • perform a full pointing session
       • beam maps of Uranus in total power AND polarimetry mode
       • polarized beam maps of QSOs, in particular polarized beam maps of 3C286
       • take also de-focused beam maps (with few different focus positions; be aware that this takes quite some time). The aim is to determine the best offset to use in order to have the best focus on avg over the whole focal surface (at the moment this is the "famous" 0.2 mm offset).
       • perform the full characterization of the arrays and NEFD in total power. Preferred targets:

         • 1h on HLS (bright source) ; older scans are available before any upgrade (telescope and NIKA2)
           

         • first assessment of new sensitivity. if good, then spend time on G2 (faint source)
         • deep integration on faint source G2 (5-10 hours) ; older scans are available before any upgrade (telescope and NIKA2)
         • Orion-B big maps with extended emission ; older scans are available before 30m painting and after painting (before NIKA upgrade)
         • M8182 big maps with empty sky, a bright compact source and a faint extended source ; older scans are available during new servo system upgrade, before 30m painting
       • perform the full characterization of NIKA2-Pol. If the external calibrator is confirmed to be working properly, use it too! Preferred targets:
         • polarimetry QSOs
         • polarimetry Crab Nebula
         • beam map on 3C286
         • beam map Uranus in pol-mode
       • If the external calibrator is confirmed to be working properly, takes some scans with the external calibrator on and off. We need to characterize the zero level of the external calibrator. To this aim, short scans are sufficient.
       • the first week of re-commissioning ends on March 25th

       • two extra days are booked for NIKA2 on March 30th to April 1st. We have decided that we will not reopen the instrument in these days, because we will wait for a thorough data analysis before taking a decision. Therefore these extra days will be used to continue the re-commisisoning

       • if necessary, a further re-commissioning week will happen either on the last week of May, or on the first week of June

Second part of the re-commissioning

Either in the case that the cryostat will be opened a second time, or will not be re-opened but this re-commissioning week is not enough to perform all needed observations, we will have a further re-commissioning period.

It will take place during the last week of May or during the first week of June. We can reserve only one week.

If this second chance is washed away by bad weather, we will shift to September