Advanced modelling of the Planck-LFI radiometers

The Low Frequency Instrument (LFI) is a radiometer array covering the 30-70 GHz spectral range on-board the ESA Planck satellite, launched on May 14th, 2009 to observe the cosmic microwave background (CMB) with unprecedented precision. In this paper we describe the development and validation of a software model of the LFI pseudo-correlation receivers which enables to reproduce and predict all the main system parameters of interest as measured at each of the 44 LFI detectors. These include system total gain, noise temperature, band-pass response, non-linear response. The LFI Advanced RF Model (LARFM) has been constructed by using commercial software tools and data of each radiometer component as measured at single unit level. The LARFM has been successfully used to reproduce the LFI behavior observed during the LFI ground-test campaign. The model is an essential element in the database of LFI data processing center and will be available for any detailed study of radiometer behaviour during the survey.Comment: 21 pages, 15 figures, this paper is part of the Prelaunch status LFI papers published on JINST: http://www.iop.org/EJ/journal/-page=extra.proc5/jins

Design, development and verification of the 30 and 44 GHz front-end modules for the Planck Low Frequency Instrument

We give a description of the design, construction and testing of the 30 and 44 GHz Front End Modules (FEMs) for the Low Frequency Instrument (LFI) of the Planck mission to be launched in 2009. The scientific requirements of the mission determine the performance parameters to be met by the FEMs, including their linear polarization characteristics. The FEM design is that of a differential pseudo-correlation radiometer in which the signal from the sky is compared with a 4-K blackbody load. The Low Noise Amplifier (LNA) at the heart of the FEM is based on indium phosphide High Electron Mobility Transistors (HEMTs). The radiometer incorporates a novel phase-switch design which gives excellent amplitude and phase match across the band. The noise temperature requirements are met within the measurement errors at the two frequencies. For the most sensitive LNAs, the noise temperature at the band centre is 3 and 5 times the quantum limit at 30 and 44 GHz respectively. For some of the FEMs, the noise temperature is still falling as the ambient temperature is reduced to 20 K. Stability tests of the FEMs, including a measurement of the 1/f knee frequency, also meet mission requirements. The 30 and 44 GHz FEMs have met or bettered the mission requirements in all critical aspects. The most sensitive LNAs have reached new limits of noise temperature for HEMTs at their band centres. The FEMs have well-defined linear polarization characteristcs.Comment: 39 pages, 33 figures (33 EPS files), 12 tables. Planck LFI technical papers published by JINST: http://www.iop.org/EJ/journal/-page=extra.proc5/1748-022

Dynamic validation of the Planck/LFI thermal model

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.Comment: Planck LFI technical papers published by JINST: http://www.iop.org/EJ/journal/-page=extra.proc5/1748-022

THE EFFECTS OF ION IRRADIATION ON THE EVOLUTION OF THE CARRIER OF THE 3.4 MICRON INTERSTELLAR ABSORPTION BAND

Carbon grains in the interstellar medium evolve through exposure to UV photons, heat, gas, and cosmic rays. Understanding their formation, evolution, and destruction is an essential component of evaluating the composition of the dust available for newly forming planetary systems. The 3.4 lm absorption band, attributed to the aliphatic C"H stretch vibration, is a useful probe of the degree to which energetic processing affects hydrogenated carbon grains. Here we report on the effects of ion bombardment of two different kinds of nano-size hydrogenated carbon grains with different hydrogen content. Grain samples, both with and without a mantle of H2O ice, were irradiated with 30 keV He + to simulate cosmic-ray processing in both diffuse and dense interstellar medium conditions. The ion fluences ranged between 1:5 � 10 13 and 7:9 � 10 15 ions cm � 2 . Infrared and Raman spectroscopy were used to study the effects of ion irradiation on grains. In both the dense and diffuse interstellar medium simulations, ion bombardment led to a reduction of the 3.4 lm band intensity. To discuss the effects of cosmic-ray irradiation of interstellar hydrogenated carbon materials we adopt the approximation of 1 MeV monoenergetic protons. An estimate of the C"H bond destruction cross section by 1 MeV protons was made based on experiments using 30 keV He + ions and model calculations. In combination with results from our previous studies, which focused on UV irradiation and thermal H atom bombardment, the present results indicate that the C"H bond destruction by fastcolliding charged particles is negligible with respect to that of UV photons in the diffuse ISM. However, in dense cloud regions, cosmic-ray bombardment is the most significant C"H bond destruction mechanism when the optical depth corresponds to values of the visual extinction larger than � 5 mag. The results presented here strengthen the new interpretation of the evolution of the interstellar aliphatic component (i.e., the C"H bonds in the CH2 and CH3 groups) as evidenced by the presence of the 3.4 lm absorption band in the diffuse medium and the absence of such a signature in the dense cloud environment. The evolutionary transformation of carbon grains, induced by H atoms, UV photons, and cosmic rays, indicates that C"H bonds are readily formed, in situ, in the diffuse interstellar medium and are destroyed in the dense cloud environment

Kinesin-13s form rings around microtubules

Kinesin is a superfamily of motor proteins that uses the energy of adenosine triphosphate hydrolysis to move and generate force along microtubules. A notable exception to this general description is found in the kinesin-13 family that actively depolymerizes microtubules rather than actively moving along them. This depolymerization activity is important in mitosis during chromosome segregation. It is still not fully clear by which mechanism kinesin-13s depolymerize microtubules. To address this issue, we used electron microscopy to investigate the interaction of kinesin-13s with microtubules. Surprisingly, we found that proteins of the kinesin-13 family form rings and spirals around microtubules. This is the first report of this type of oligomeric structure for any kinesin protein. These rings may allow kinesin-13s to stay at the ends of microtubules during depolymerization

LFI 30 and 44 GHz receivers Back-End Modules

The 30 and 44 GHz Back End Modules (BEM) for the Planck Low Frequency Instrument are broadband receivers (20% relative bandwidth) working at room temperature. The signals coming from the Front End Module are amplified, band pass filtered and finally converted to DC by a detector diode. Each receiver has two identical branches following the differential scheme of the Planck radiometers. The BEM design is based on MMIC Low Noise Amplifiers using GaAs P-HEMT devices, microstrip filters and Schottky diode detectors. Their manufacturing development has included elegant breadboard prototypes and finally qualification and flight model units. Electrical, mechanical and environmental tests were carried out for the characterization and verification of the manufactured BEMs. A description of the 30 and 44 GHz Back End Modules of Planck-LFI radiometers is given, with details of the tests done to determine their electrical and environmental performances. The electrical performances of the 30 and 44 GHz Back End Modules: frequency response, effective bandwidth, equivalent noise temperature, 1/f noise and linearity are presented

Planck-LFI: Design and Performance of the 4 Kelvin Reference Load Unit

The LFI radiometers use a pseudo-correlation design where the signal from the sky is continuously compared with a stable reference signal, provided by a cryogenic reference load system. The reference unit is composed by small pyramidal horns, one for each radiometer, 22 in total, facing small absorbing targets, made of a commercial resin ECCOSORB CR (TM), cooled to approximately 4.5 K. Horns and targets are separated by a small gap to allow thermal decoupling. Target and horn design is optimized for each of the LFI bands, centered at 70, 44 and 30 GHz. Pyramidal horns are either machined inside the radiometer 20K module or connected via external electro-formed bended waveguides. The requirement of high stability of the reference signal imposed a careful design for the radiometric and thermal properties of the loads. Materials used for the manufacturing have been characterized for thermal, RF and mechanical properties. We describe in this paper the design and the performance of the reference system.Comment: This is an author-created, un-copyedited version of an article accepted for publication in JINST. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The definitive publisher authenticated version is available online at [10.1088/1748-0221/4/12/T12006]. 14 pages, 34 figure

Analysis of cosmic materials: Results on carbon and silicate laboratory analogues

Carbon and silicates are two of the main components of cosmic dust. They change nature through different evolutionary phases, according to the cosmic environment and the experienced processing. To understand the evolution of cosmic materials the study of "laboratory analogues" represents a powerful tool. In this context, systematic analyses are performed at the cosmic physics laboratory of Naples on solid particles, synthesised and processed under carefully controlled conditions. Different kinds of carbon and silicate samples are produced under various environmental conditions and exposed to processes (e.g. thermal annealing, UV irradiation and ion bombardment). The comparative analysis of the results allows us to link intrinsic properties (such as chemical composition and structure) to the optical behaviour of grains. This study offers the opportunity to interpret observations concerning the composition of small bodies in the Solar System, such as spectroscopic results obtained for comets by the Infrared Space Observatory (ISO). Several open questions remain, however, unsolved and await results from new laboratory experiments. ©1999 COSPAR. Published by Elsevier Science Ltd