UNIVERSITÀ DEGLI STUDI DI MILANO Facoltà di scienze matematiche, fisiche e naturali DOTTORATO DI RICERCA IN FISICA, ASTROFISICA E FISICA APPLICATA (CICLO XX) Data Analysis of the Planck/LFI QM/FM Tests Tesi di dottorato di MAURIZIO TOMASI Matricola n. R06115 CODICE PACS 95.85.E Coordinatore: Prof. GIANPAOLO BELLINI Tutor: Prof. MARCO BERSANELLI Referee: Prof. GIORGIO SIRONI Typeset with LATEX. This thesis is available in electronic format (Adobe Portable Document For- mat, PDF) at http://www.geocities.com/zio_tom78/. Contents Introduction v 1 Our Universe and the Cosmic Microwave Background 1 1.1 The Birth of Cosmology and the Ancient Models of the Uni- verse . 2 1.1.1 Greek Philosophy and the Origin of the World . 2 1.1.2 Cosmology in the Middle Ages . 4 1.2 From Copernicus to the Crisis of Heliocentrism . 6 1.2.1 The Heliocentric Cosmological Model . 6 1.2.2 The First Mathematical Models in Cosmology . 6 1.3 Cosmology in the XX Century . 7 1.3.1 Einstein’s Static Cosmological Model . 7 1.3.2 The Friedmann’s Model . 9 1.3.3 Hubble’s Law of Galaxy Recession . 10 1.4 The Cosmic Microwave Background . 12 1.4.1 Gamow’s Prediction of a Relic Background . 12 1.4.2 First Detection of the CMB . 12 1.4.3 The Inflationary Universe . 14 1.4.4 First CMB Anisotropies Experiments . 15 1.4.5 The Science of CMB Anisotropies . 17 1.4.6 Origin of CMB Anisotropies . 18 1.4.7 Importance of the CMB for Physics . 20 1.4.8 The WMAP Experiment . 23 2 The Planck Mission and the LFI Instrument 27 2.1 Role of the Planck Project in the CMB Science . 28 2.2 The High Frequency Instrument (HFI) . 31 2.3 The Low Frequency Instrument (LFI) . 33 2.3.1 Overview of the Instrument . 33 2.3.2 Structure of an LFI Radiometer . 34 2.4 The Planck Cooling System . 36 2.4.1 The Sorption Cooler . 36 2.4.2 The Joule-Thomson Cooler . 38 i ii CONTENTS 2.4.3 The Dilution Cooler . 38 2.5 The Planck/LFI Ground Test Campaigns . 38 2.5.1 Overview of the Test Stages . 38 2.5.2 The Radiometric Chain Assembly (RCA) Tests . 42 2.5.3 The Radiometer Array Assembly (RAA) Tests . 46 3 Dynamic Thermal Analysis of the LFI Focal Plane 49 3.1 Need for a Thermal Characterization of the Focal Plane . 50 3.2 General Concepts about Thermal Transfer . 52 3.2.1 Derivation of the General Equation . 52 3.2.2 Thermal Transfer Functions . 53 3.3 Numerical Thermal Analysis . 54 3.3.1 Purpose of Numerical Analysis . 54 3.3.2 Characteristics of a Numerical Model . 55 3.3.3 Calibration of a Numerical Thermal Model . 56 3.4 Experimental Measurements of the Transfer Functions . 58 3.4.1 The Fourier Transform Method . 59 3.4.2 The Non-linear Fitting Method . 60 3.4.3 The Direct Estimation Method . 60 3.4.4 Overall comparison of the three methods . 63 3.5 Data Analysis of the QM Tests . 65 3.6 Data Analysis of the FM Tests . 70 3.6.1 The Test Procedure . 70 3.6.2 Analysis of the Results . 71 3.7 Conclusions . 76 4 Calibration and Verification of the LFI Data Compressor 81 4.1 Principles of the LFI Data Compressor . 82 4.1.1 Need for a Data Compressor . 82 4.1.2 Principles of Data Compression . 83 4.1.3 Details of the LFI Data Compressor . 86 4.1.4 The Radiometer Electronics (REBA) Acquisition Modes 87 4.1.5 Requirements on Data Compression . 87 4.2 Calibration of the LFI Data Compressor . 88 4.3 Verification of the LFI Data Compressor . 91 4.4 Detection of Jumps in the Radiometric Output . 92 5 Verification and Calibration of LFI with LIFE 97 5.1 LIFE, an Analysis Tool for the LFI Test Campaigns . 98 5.2 Radiometric Test Analysis with LIFE: the RaNA Package . 100 5.2.1 Format of the LFI RCA Data . 100 5.2.2 The RaNA Data Analysis Modules . 101 5.3 LFI Test Analysis with LIFE: the LAMA Package . 101 5.3.1 Format of the LFI RAA Data . 101 CONTENTS iii 5.3.2 Tree Representation of RAA Data under Lama . 102 5.3.3 Support for Multiple Measure Units in the Data . 106 5.3.4 Extension of the RaNA Approach to Multiple Feed- Horns . 107 5.3.5 Downsampling of Radiometric Outputs . 107 5.3.6 Accessing data . 108 5.3.7 The Lama Link module . 109 5.4 Future Developments of LIFE . 113 6 Conclusions and Future Work 115 6.1 Use of LIFE in the LFI QM/FM Tests . 115 6.2 In-flight Testing and the Future of LIFE . 116 6.2.1 Use in the next Satellite Tests . 116 6.2.2 Use in Flight . 116 A Algorithmic Asymptotic Behavior 119 List of Acronyms 121 iv CONTENTS Introduction This thesis is the result of a work lasted three years and carried out at the Istituto Nazionale di Astrofisica e Fisica Cosmica (INAF) in Milan. In my work, I have contributed to the ground calibration of the Low Frequency Instrument (LFI), one of the two instruments that will fly on the Planck satellite, a new-generation experiment for the measurement of tempera- ture and polarization anisotropies in the Cosmic Microwave Background (CMB). Planck (http://www.rssd.esa.int/Planck) is an ESA project with instruments funded by ESA member states (in particular the PI countries: France and Italy), and with special contributions from Denmark and NASA (USA). In this thesis I will also illustrate my contributions to the implemen- tation of the Lfi Integrated perFormance Evaluator (LIFE) software pack- age and will show some of its applications. LIFE has been a key compo- nent in the testing of the qualification and flight models (QM and FM) of the Planck/LFI instrument that were done in the period July 2004–October 2006 in the Alcatel/Alenia Space laboratories of Milan (Italy). Since Novem- ber 2006, many of these tests are being repeated on the full integrated satel- lite in the Thales/Alenia Space laboratories of Cannes (France), according to the Planck calibration plan. The organization of this thesis is as follows: • Chapter 1 gives an historical introduction to cosmology and CMB, and briefly discusses the most important experiments in the field of CMB measurements. Although somewhat unusual, I have sketched a historical approach, introducing modern cosmology in a wider con- test. • Chapter 2 provides an overview of the Planck space mission to mea- sure the temperature and polarization anisotropies of the CMB. I will concentrate on the LFI, an array of radiometers in the 30 ÷ 70 GHz frequency range. • To achieve its ambitious scientific requirements, LFI needs an exten- sive and detailed calibration campaign, started in July 2004 and still v vi Chapter 0. Introduction continuing. In chapters 3 and 4 I will discuss two calibration tasks that were under my direct responsability: – Chapter 3 reports on the thermal calibration activity that char- acterized the dynamical behavior of the Planck/LFI focal plane when temperature fluctuations are induced on it. Such testing is extremely important for achieving the scientific goals of Planck, since LFI requires high temperature stability to reduce the im- pact of systematic errors on its performances. – In order to be able to send all the scientific information acquired during flight to Earth, LFI implements a data compressor. Chap- ter 4 explains the concept of the LFI compressor and discusses the tests we have made to calibrate and verify its performances. • Chapter 5 discusses in full detail the implementation of the LIFE soft- ware package. LIFE is the tool that has been used to analyze the LFI tests acquired during the test campaigns. I was part of the LIFE de- velopment core team and have designed and coordinated some key features of the software. Here I will discuss my contributions to this activity. • Finally, chapter 6 sums up the contents of this work and explains the next LFI calibration stages and the foreseen development of the LIFE for its use during the survey observations. CHAPTER 1 Our Universe and the Cosmic Microwave Background MASHA: To live and not to understand why cranes fly; why children are born; why there are stars in the sky. You’ve got to know what you’re living for or else it’s all nonsense and waste. Anton Chekhov, “Three sisters”, Act II Let us seek with the desire to find, and find with the desire to seek still more. St. Augustine, quoted in “Address of Pope Paul VI to men of thought and science”, December 8th, 1965 In this chapter I will provide a short historical overview about the his- tory of Cosmology and measurements of the Cosmic Microwave Background (CMB). This chapter will consider a broad time span, starting from the very first Greek philosophers (VI century b.C.) and ending with the most recent advances in observational cosmology (WMAP). The struggle to understand the nature of our Universe has always been present in mankind. Although this chapter cannot be a complete account of the development of cosmological understanding, nonetheless it tries to illustrate some of the great efforts spent in the last two millennia1 — and still continuing — to grasp a full “cosmic vision”. The status of present-day cosmology and of CMB science in particular is then discussed in greater detail. The structure of this chapter is as follows: 1I chose not to include in this short review — despite their unquestionable interest — those cultures that have had no particular influence on the development of modern scien- tific cosmology (e.g.