NIKA2 run #5 September/October 2016

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Goals of the run

Upgrade the instrument with new hardware

• new dichroic (flattened on membrane, vs more floppy before),
• new 2mm array (less pixels, but bigger to conserve FOV),
• new corrugated lenses and window (the whole 8 dioptres on the optical path all corrugated with small pyramids vs none before),

• new NIKEL boards for array 2 and 3 (=> v3 everywhere vs v1, v2 and v3 previously).

Redo and improve tests started since run 1

1. Check data & flags consistency & synchronization: Raw, FIT for Pipeline, IMBFIT.

2. Optimisation of tone comb position: is it possible to optimize the number of A1 and A3 pixels fitting the NIKEL bandwidth ?
3. Test possible improvement on synchronization of NIKA2 data with telescope online scans information (e.g. subscan start and stop, tuning and decalage time and duration, etc.). Check with Granada staff if we have now a more direct link with ELVIN or if we use instead a UDP connection to a nika2-a port.
4. Test possible improvement on synchronization of NIKA2 data within itself (NIKEL boxes vs boxes internal consistency when recovering from lost synchro), and with telescope antenna-imbfits information (e.g. coordinates, zig-zag on beam maps).

5. More specifically about synchronization of NIKA2 samples with telescope coordinates: the systematic time shifts between boards should be solved now with the new ones (see previous point), so PPS time should be sufficient to cope with any possible fluctuations of the UDP time distribution used to define the UTC time in each box → to make this test do simply beam maps at various speed, elevation, subscan direction and acquisition frequency.

6. Investigate optimal threshold for decalage between subscan (systematic ftone jumps between subscans will kill the sky noise low frequency decorrelation, so decalage between subscan should be only in case of high background sky variations that would be so big that we would loose the resonances otherwise, hence the scan).
7. Perform several dark sessions, at least one at the beginning and one at the end of the run, possibly one per day, in order to study the features in the data that don't come from the sky, but from the instrument itself and possibly its environment in the receiver cabin.

8. Beams characterization is again the priority (after quality checks listed on previous items): beam maps repeated for statistics is the main tool, using XYZ focus optimization and best weather. Pay attention also at the possible dependence with elevation.

9. Check and understand possible pointing variations (e.g. vs elevation, vs azimuth, vs time, vs focus).
10. Investigate optimal beam map strategy (1 map vs 3x submaps).

11. Test very large beam maps (> 30') to investigate error beams, keeping same integration time (scan faster).

12. Check and understand non-symmetrical noise distribution.
13. Check jumps and instabilities.
14. Check expected diminution of cross-talk on array 2 and better stability.
15. Elements that come "for free" with many beam maps: increase statistics on kid stability, photometry, sensitivity and time line features.
16. Regular skydips: at least once per day.
17. Check and understand possible flag problems during skydips and other scan types.
18. A session of KIDs working point optimization (e.g. gain, dftone modulation frequency and amplitude, etc. see with specialists of the instrument like Alessandro, Martino, Alain...) ?
19. Continue observations of many calibrators to monitor our sensitivity and photometry.
20. Continue tests on polarization mode: beam maps, various scan speed and sampling frequencies.
21. Deep integration on a sub mJy source for several hours (~10), to check stability of sensitivity (rms vs sqrt(time)).
22. Depending on the completion of previous items, go for more advanced characterizations, and mapping extended features (test various map making strategies in analysis software [Pipeline, scanamorphos, etc.]).

    1. The nearby-galaxies team suggests to map the face-on galaxy NGC6946 to make a show case for mapping extended features. <CK, 5-Jul-2016>

    2. Consider continue mapping NGC891 to make a show case for the polarization mode (edge on galaxy → ~5% dust polar expected...).

23. Possibly test the external calibrator that will be finalized during the summer, using an external mirror to redirect part of its flux into the instrument FOV. Placing it in the secondary could be considered only after we prove we can handle it, use it, that it is useful (e.g. help decorrelate atmosphere from acquisition gain instabilities), and small and light enough for the lodging into M2. Prior to any installation of the calibrator in the secondary, a careful assessment of the risks for the secondary and wobbler must to be done. <CK, 5-July-2016>

The detailed characterization plan established for run 1 needs to be updated.
A more concise version, including a status summary might be written ... when I find time for this... (SL).

Complementary information

Beams characterization from previous runs and expectations with the upgrade:

• At 2mm the dichroic deformation was dominant, and the array more unstable than 1mm arrays (CPW vs micro strip design or only lower density of resonances in electronic bandwidth ?). → Should be fixed now.

• On all bands there is an asymmetry on beams pedestal, which is also visible on lab measures, indicating a possible optics problem in the cryostat. → There's practically no chance that the new lenses will improve this.

• On all bands the beam is easily elliptic, and the 1^st side lobe is at 10% level of the peak while predictions for diffraction on perfect 30m diameter aperture gives circular beam and the 1^st side lobe at 2% of the peak. Optics simulations show non-optimal XYZ focus, and telescope astigmatism (due to high order deformations terms not compensated by the homology structure of the parabola), may explain the behavior of ellipticity with focus, and the level of the 1^st side lobe. But larger scale beam structure, holography measurements, and beam obtained with heterodyne instruments suggest NIKA2 might suffer from another additional component distorting its beams. Only beam maps at optimal XYZ focus and sky can allow investigating this problem.

• We expect and increase of the transmission efficiency by >25% using the corrugated lenses instead of the previous smooth surfaces.

Upgrades on acquisition side

• The old nika2-a computer will be now dedicated to acquisition only, the new nika2-b twin will be used for data processing.
• The hard disk storage has been bought.

• What about the upgrade on live scan information transmission (ELVIN or new UDP or bidirectional link) ?

• Is there some upgrades on acquisition software (Camadia) and online data processing (Pipeline), to fix or cope with possible technical problems (e.g. NIKEL box synchro, with possible mismatch of times ; tuning during scans ; uncorrelated oscillations in timelines ; focus errors ...) ?

Schedule of the run

Telescope Schedule week 1 → Hardware upgrade on Fri 16 & Sat 17 of September.
Telescope Schedule weeks 2 → Test on sky after cool down on Sat 24 & Sun 25.
Telescope Schedule weeks 3 → 16h/day from Tue 4 to Tue 11 of October.

All the persons who will participate to the run must appear in the table below; each one must have informed at least Samuel, Esther (for the rooms in Granada and at the telescope), Beatrice (for the ones who fly on IRAM funds, see NIKA2 travel rules).

Staff of the run: table of the nights spent at the observatory for the NIKA2 collaboration members participating to the run (T = Tuesday, S = Saturday, 1 = night scheduled at the telescope, g = night in Granada office, t = travel with CNRS truck). "?" means not strictly necessary ... better if. The period 26 to 29/09 is heavy maintenance so nobody from NIKA2 needs to be there.
First day at the telescope: Friday, September 16, 2016.

(*) Count persons from the NIKA collaboration not from IRAM Granada.

IRAM's Astronomer on Duty.