NIKA2 run #5 September 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 stated since run 1 on the upgraded instrument.

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

2. Optimisation of tone comb position: arrays 1 and 3 have systematically about one line of pixels missing per multiplexed feed line; this is due to the limited bandwidth of the NIKEL boards w.r.t. the resonance frequencies span, we may recover a number of pixels by optimizing the tone comb position.
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: to test if we the previous systematic errors are solved with the new boards, and that using PPS time is sufficient to cope with possible fluctuations of the DP time distribution used to define the UTC time in each box → to make this test do beam maps at various speed, elevation, scan pattern (not only zig-zag, but also only increasing azimuth, only decreasing azimuth etc.), and also various acquisition frequency.

6. Investigate best threshold for decalage between subscan, because 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. An optimum has to be found.
7. Check and understand possible pointing variations (e.g. vs elevation, vs azimuth, vs time, vs focus).
8. Check and understand possible flag problems during skydips.
9. Investigate optimal beam map strategy (1 map vs 3x submaps).
10. Check and understand non-symmetrical noise distribution.
11. Check jumps and instabilities.
12. Check expected diminution of cross-talk on array 2 and better stability.
13. 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. Pay attention also at the possible dependence with elevation.
14. Elements that come "for free" with many beam maps: increase statistics on kid stability, photometry, sensitivity and time line features.
15. Regular skydips: at least once per day.
16. 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...) ?
17. Continue observations of many calibrators to monitor our sensitivity and photometry.
18. Continue tests on polarization mode: beam maps, various scan speed and sampling frequencies.
19. Deep integration on a sub mJy source for several hours (~10), to check stability of sensitivity (rms vs sqrt(time)).
20. 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.]).

21. Consider NGC891 to make a show case for NIKA2, in particular for the polarization mode (edge on galaxy → ~5% dust polar expected...)

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 ?). → 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 1st side lobe is at 10% level of the peak and elliptic against 2% of the peak and circular predicted for diffraction on perfect 30m diameter aperture. 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 such shape. 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.

The detailed characterization plan established for run 1 is still valid, but needs to be updated; you can still look at it to check possible missing action items: http://www.iram.fr/wiki/nika2/index.php/NIKA2_Run1_30m_CharacterizationPlan
A more concise version, including a status summary might be written ... when I find time for this... (SL).

Preparation of the run

Telescope Schedule week 1 ==> 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 2 ==> 16h/day from Tue 4 to Tue 11 of October.

Staff of the run: table of the nights spent at the observatory for the NIKA2 collaboration members participating to the run (T means Tuesday, S means Saturday, first night with NIKA2 staff is Tuesday 29 September, last night is Monday 9 November, 1 stands for night scheduled at the telescope, p stands for possible extension in case of problem with the cryostat).

AOD: A.Sievers/P.Garcia on week 1; F.Damour/J.L.Santaren (operators) on week 2. Astronomer on Duty