Dynamic validation of the Planck-LFI thermal model

Abstract

The Low Frequency Instrument (LFI) is an array of cryogenically cooled radiometers on board the Planck satellite, designed to measure the temperature and polarization anisotropies of the cosmic microwave backgrond (CMB) at 30, 44 and 70 GHz. The thermal requirements of the LFI, and in particular the stringent limits to acceptable thermal fluctuations in the 20 K focal plane, are a critical element to achieve the instrument scientific performance. Thermal tests were carried out as part of the on-ground calibration campaign at various stages of instrument integration. In this paper we describe the results and analysis of the tests on the LFI flight model (FM) performed at Thales Laboratories in Milan (Italy) during 2006, with the purpose of experimentally sampling the thermal transfer functions and consequently validating the numerical thermal model describing the dynamic response of the LFI focal plane. This model has been used extensively to assess the ability of LFI to achieve its scientific goals: its validation is therefore extremely important in the context of the Planck mission. Our analysis shows that the measured thermal properties of the instrument show a thermal damping level better than predicted, therefore further reducing the expected systematic effect induced in the LFI maps. We then propose an explanation of the increased damping in terms of non-ideal thermal contacts.

Planckpre-launch status: Design and description of the Low Frequency Instrument

“…We derived stringent requirements (δT < 100 mK peak-to-peak) on acceptable temperature fluctuations at the interfaces of the 20 K cooler with LFI (LVHX2). Testing at instrument level (Tomasi et al 2010) and at system level have verified the design consistency. …”

“…Temperature sensors are placed in strategic locations of the instrument flight model to monitor temperature values and fluctuations during both ground calibration (Tomasi et al 2010) and in-flight operation. Figure 21 shows the 12 sensors in the focal plane unit, five of which have higher sensitivity and a narrower dynamic range (14 to 26.5 K) to adequately trace temperature fluctuations.…”

Planck2013 results. III. LFI systematic uncertainties

“…Thermal systematic effects maps have been generated using a simulation strategy that combines in-flight temperature sensor measurements (Mennella et al 2010), thermal modelling of the propagation of temperature fluctuations (Tomasi et al 2010) and radiometric transfer functions measured during ground tests (Terenzi et al 2009b). Here we sketch the procedure used to combine these data into systematic effect maps.…”

Effect of Fourier filters in removing periodic systematic effects from CMB data

“…Details of the thermal damping provided by the instrument structure and of the radiometric coupling functions are beyond the scope of this paper and not discussed here. Interested readers can find details in Terenzi et al (2009) and Tomasi et al (2010).…”

“…from house-keeping telemetry such us the temperature recorded by a sensor on the instrument focal plane) is available. To remove thermal effects, for example, an effective use of temperature sensor data in non-blind codes calls for detailed knowledge about the amplitude and phase of thermal damping between the position of the temperature sensors and the detectors (see, for example, Tomasi et al 2010). A&A 529, A141 (2011) In this paper, we consider the application of Fourier filters to CMB datasets, with particular reference to full-sky surveys performed from space.…”