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| 1) The stray signal is small but present. We estimate that is | 1) The stray signal is small but present. The residual signal is few per cent at 1xOmega, much less for the others armonics. 2) Very small differences with the plate or without the plate. '''We Decides to keep the configuration without the plate for the rest of the observing campaign.''' '''The mechanical rotational frequency is 2.98 Hz, The acquisition frequency is 47.68 Hz. This means 4 indipendent point per HWP tour.''' |
Contents
January 19th 2015
10h. The first part of the NIKA Polar Team arrived: Andrea, Alessia, Nicolas.
12h. Helping the open pool team to make observations.
January 20th 2015
10h. The rest of the NIKA polar team arrived: Vincent and Philippe.
11h. mppsync does not work with the current version of the acquisition. We update the version 6470 only on the mppsync instrument and everything started to work.
13h. Polariser, HWP and WG put into the beam at the nominal position.
14h. We performed several tests to check the best configuration of the polariser. The question was: is it really necessary to put an aluminum plate in order to mask all the mechanical parts which turns in front of the cryostat? If we do this, we must recule the WG by 1-1.5 cm in the direction of the cryostat window running the risk to loose some sky photons.
In the following plot some results of our tests (the background is 300K, the mechanical rotation is 3Hz):
Spectrum of the signal with aluminum foils closing the window (we want to test if any armonics can be in the signal by magnetics, electrical or vibration spurious signals.
Spectrum of the signal with the cryostat window open, without the plate.
Spectrum of the signal with the cryostat window open and the plate.
We can conclude:
1) The stray signal is small but present. The residual signal is few per cent at 1xOmega, much less for the others armonics. 2) Very small differences with the plate or without the plate.
We Decides to keep the configuration without the plate for the rest of the observing campaign.
The mechanical rotational frequency is 2.98 Hz, The acquisition frequency is 47.68 Hz. This means 4 indipendent point per HWP tour.