The SPIDER CMB Polarimeter
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The SPIDER CMB Polarimeter Thesis by Amy R. Trangsrud In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy California Institute of Technology Pasadena, California 2012 (Defended July 26, 2011) ii c 2012 Amy R. Trangsrud All Rights Reserved iii Acknowledgements My journey here began one September day, walking into Andrew Lange’s office in the basement of West Bridge, excited and nervous. In a moment he saw me, took me in, welcomed me, and set me at ease. Then we were off like a whirlwind. We walked briskly over to the high bay, where BICEP was nearing deployment. Andrew sent me up on a ladder to take in the technology, while he told me about B-modes, Spider, and BICEP2, his eyes alight with excitement. He oozed curiosity, ingenuity, and enthusiasm. Back in Bridge, he toured me through the White Dewar lab, where Chao-Lin Kuo was beam mapping. I remember Andrew saying, this could be you in a couple years. Sure enough, it was. Andrew was exceptional in his ability to advise, understand, and nurture his students. When I sat down with him, he would immediately focus in on my situation and perspective, and on how he could best aid me in moving forward. He saw things in context, and gave science a sense of humanity. Andrew understood that the relationship between a PhD student and an advisor is a special one; one that plants a seed that shapes the student over a lifetime. So it will be for me. I am grateful and honored that Andrew shared his spirit with me, and I will carry and treasure his mentorship and example. Thank you Andrew. When we lost Andrew, our Obscos team grew even stronger as a family. Kathy Deniston, Sunil Golwala, and Jamie Bock, while handling their own grief, opened their wings like protective parents, and swept everyone under. They were heros in a dark time. Simply put, we would not have a group without Kathy. She and Barbara Wertz are simultaneously the glue that holds everything together and the grease that keeps everything moving. To this day, I am not sure how Kathy does it all. Sunil selflessly and apparently without hesitation took me, and others, under his advi- sorship when we were orphaned midstride. He has been an important part of my education from the beginning of my work here. Sunil affected me most notably with his willingness to spontaneously sit down to teach us something, and with his ability to explain physical iv concepts clearly and to derive relevant results on a moment’s notice. There is no one in this group with whom I have worked as closely and over as many years as Jamie. Spider is made compelling by its detector technology more than anything else. Jamie is the core of the detector development effort, and therefore at the root of everything that we do. After four years of Thursday detector meetings, I sincerely hope that a bit of Jamie’s deep understanding and intuition have rubbed off on me. I appreciate all that I have learned from him not only about the devices themselves, but about the process of developing new technology, patiently, methodically, and creatively. I have had a number of mentors over my years here, and I appreciate each and every one of them for mentoring me, and showing me their style of science. Matt Kenyon at JPL showed me how to fly by the seat of my pants and get a lot done. Bill Jones had a way of making any task feel fun and valuable. Chao-Lin Kuo showed me how to manage experiments from start to end, and operate my own cryogenic test bed. Jeff Filippini and Marc Runyan mentored me in receiver characterization, and provided opportunities for me to take important roles in our team. There are many others. I would like to thank all of my colleagues and collaborators here at Caltech/JPL, and around the world. Caltech is a community, and my memories of this place will extend well beyond the walls of the astronomy building. While enrolled here I met the love of my life, was sexually harassed by a janitor, was awarded a fellowship, had a life-changing surgery, lost my advisor, and got married. My friends have been with me through it all, and made this journey possible. You all know who you are. Thank you! There is no easy way to put into words the debt I owe to my Mom and Dad for their love, support, sacrifices, patience and just plain hard work in helping me to grow into the person that I am, and in filling my life with an incredible abundance of opportunities. It takes a special person to love and marry an academic. Especially a mad scientist, and, worst of all, an experimentalist. Lorelei has stood by my side through all my work here. She has driven with me to campus late at night and on weekends for cryogen fills, and sent me off at the airport as I embarked on a month-long deployment to the South Pole. She has patiently supported me and been my cheerleader as, every six months or so, I have told her about some change in my deployment schedule or planned graduation timeline. Most of all, she has been my partner in life and love. v The SPIDER Collaboration California Institute of Technology J. P. Filippini, S. Golwala, V. V. Hristov, P. V. Mason, T. A. Morford, M. C. Runyan, M. A. Schenker, A. R. Trangsrud, R. S. Tucker Cardiff University P. A. R. Ade, C. Tucker Case Western Reserve University R. Bihary, S. Bryan, T. E. Montroy, J. E. Ruhl Imperial College C. N. Clark, C. R. Contaldi, D. T. O’Dea JPL J. J. Bock, J. A. Bonetti, B. P. Crill, O. Dor´e, W. Holmes, A. D. Turner Kavli Institute for Cosmology, University of Cambridge C. J. MacTavish NIST G. Hilton, K. Irwin, C. Reintsema Princeton University H. C. Chiang, A. A. Fraisse, J. E. Gudmundsson, W. C. Jones, A. S. Rahlin Stanford University C. L. Kuo University of Toronto S. J. Benton, M. Farhang, L. M. Fissel, N. N. Gandilo, C. B. Netterfield, J. D. Soler, J. A. Shariff, J. R. Bond University of British Columbia M. Amiri, B. Burger, G. Davis, M. Halpern, M. Hasselfield, D. Wiebe vi Abstract Spider is a balloon-borne millimeter-wave telescope designed to study the polarization of the Cosmic Microwave Background (CMB). Spider will map 10% of the full sky with degree- scale beams to search for the distinctive inflationary gravitational wave signal on angular scales between 1◦ and 10◦, thereby probing the energy scale of inflation. In its first flight, Spider will field 2,400 antenna-coupled bolometers split between two bands centered at 93 and 148 GHz. Slot antenna arrays, band-defining microstrip filters, and superconducting bolometers are all fabricated photolithographically on a shared silicon substrate. Spider’s detectors are split amongst six monochromatic on-axis refractors in a shared helium-cooled cryostat. This thesis reviews the design of Spider and its antenna-coupled bolometers, and details the currently achieved performance of Spider’s receivers. vii Contents Acknowledgements iii The SPIDER Collaboration v Abstract vi 1 Introduction 1 1.1 The Beginning of Physical Cosmology ..................... 1 1.2 Discovery of the Cosmic Microwave Background ................ 4 1.3 CMB Statistics .................................. 5 1.4 Inflation Theory ................................. 9 1.5 CMB Temperature Anisotropies ......................... 12 1.6 CMB Polarizing Mechanisms . ........................ 13 1.7 Polarized Foregrounds .............................. 19 2 The SPIDER Balloon-Borne CMB Polarization Experiment 22 2.1 Collaboration ................................... 23 2.2 Frequency Coverage ............................... 23 2.3 Sky Coverage ................................... 26 2.4 Ballooning ..................................... 26 2.5 Cryogenics ..................................... 30 2.6 Optics ....................................... 33 2.7 Half-Wave Plates ................................. 37 2.8 Magnetic Shielding ................................ 39 2.9 Simulations . ................................. 40 viii 3 Detectors and Readout 42 3.1 Bolometric Technology Development ...................... 42 3.2 SPIDER Detector Architecture .......................... 45 3.3 Fabrication Process ................................ 49 3.4 TES Bolometer Basics .............................. 52 3.5 Readout ...................................... 58 4 Receiver Performance 61 4.1 Beam Profiles ................................... 61 4.2 Frequency Band Definition ........................... 71 4.3 Polarization Efficiency .............................. 79 4.4 Efficiency of Optical Response .......................... 80 4.5 Internal Optical Loading of Devices ....................... 86 4.6 Bolometer Properties ............................... 90 4.7 Noise Performance ................................ 94 4.8 Temperature Stability . ........................... 100 4.9 Magnetic Field Response ............................. 101 4.10 Summary and Recommendations for Future Work .............. 102 A Definitions and Methods 107 A.1 Optical Efficiency ................................. 107 A.2 Alternative Methods for Calculating Internal Loading ............ 109 B Measured Detector Parameters 112 Bibliography 124 ix List of Figures 1.1 Example of a CMB temperature and polarization map (from B2K) ...... 7 1.2 Illustration of E- and B-mode polarization patterns .............. 8 1.3 Definition of coordinate system for Thomson scattering calculation ...... 14 1.4 Measurements to date of EE and BB power spectra .............. 21 2.1 Spider bands and atmospheric emission model ................. 25 2.2 The Spider observing region ........................... 26 2.3 The Spider gondola (drawings and photos) ................... 29 2.4 The Spider flight cryostat (photo and cross-sectional drawing) ........ 31 2.5 An assembled focal plane unit and a 3He adsorption fridge (photos) ..... 32 2.6 Modular telescope insert bays in the flight cryostat (photos) ......... 34 2.7 A telescope insert (photo and cross-sectional drawing) ............. 34 2.8 A half-wave plate assembly (photos) ....................... 37 2.9 Diagram showing rotation of polarization by a half-wave plate ........ 38 2.10 Sensitivity of Spider bands to polarized dust .................. 41 3.1 A spider-web bolometer and a polarization sensitive bolometer (photos) .