Development of Cryogenic Detection Systems for a Search of the Neutron Electric Dipole Moment by Robert Dipert A Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Approved April 2019 by the Graduate Supervisory Committee: Ricardo Alarcon, Chair Ralph Chamberlin Robert Golub Tingyong Chen Kevin Schmidt ARIZONA STATE UNIVERSITY May 2019 ABSTRACT Seeking an upper limit of the Neutron Electric Dipole Moment (nEDM) is a test of charge-parity (CP) violation beyond the Standard Model. The present experimentally tested nEDM upper limit is 3x10−26 e cm. An experiment to be performed at the Oak Ridge National Lab Spallation Neutron Source (SNS) facility seeks to reach the 3 × 10−28 e cm limit. The experiment is designed to probe for a dependence of the neutron's Larmor precession frequency on an applied electric field. The experiment will use polarized helium-3 (3He) as a comagnetometer, polarization analyzer, and detector. Systematic influences on the nEDM measurement investigated in this thesis include (a) room temperature measurements on polarized 3He in a measurement cell made from the same materials as the nEDM experiment, (b) research and development of the Su- perconducting QUantum Interference Devices (SQUID) which will be used in the nEDM experiment, (c) design contributions for an experiment with nearly all the same conditions as will be present in the nEDM experiment, and (d) scintillation studies in superfluid helium II generated from alpha particles which are fundamentally similar to the nEDM scintillation process. The result of this work are steps toward achievement of a new upper limit for the nEDM experiment at the SNS facility. i ACKNOWLEDGMENTS I would like to thank Ricardo Alarcon, my adviser, who has patiently worked through my academic and personal challenges over these many years. His patience and availability were vital qualities resulting in the success of this research. Many thanks to Austin Reid, NCSU graduate student and now Indiana University post- doc. There is a unique bond which forms between those whom have experienced such a roller coaster as graduate school together. We have grown in many ways since the beginning of this journey and I look forward to seeing whom we will grow into in the future. A special place in my heart and career exist for Chris Swank, whom had graduated from NCSU a few months prior to me arriving there. He provided invaluable guidance, support, encouragement, friendship, and levity. The year we spent together at TUNL, prior to his work at CalTech, set the tone for the rest of my graduate experience and I will always look upon that year with appreciation and thankfulness. I have great appreciation for the knowledge, determination, skills, and research expe- rience offered to me by Bob Golub. He is truly a unique man and I am honored to have spent so much time with him and have had the opportunity to learn so much from him. His passion for science and never ending curiosity are beyond the scope of my comprehension. My deepest gratitude and thanks go to Toni Craige who has weathered the storm of graduate school at my side. My love has been supportive and encouraging and helped to smooth many tumultuous moments. This work would not have been possible without the efforts of many people. A short and incomplete list of people I would like to thank includes: Ekaterina Korobkina, Igor Berkutov, Larry Bartoszek, Weijun Yao, Bastiaan Driehuys, Geoff Schrank, Chris Westerfeldt, Robin Cantor, Steven Clayton, Richard Nappi, Takeyasu Ito, Nguyen Phan, Kent Leung, Qiang (Alan) Ye, Bret Carlin, Richard O'Quinn, Gary Cofer, Jerry Dahlke, David Kendellen, Srun (Jump) Sosothikul, Paul Huffman, Albert Young, Vince Cianciolo, Matt Freeman, Mike Gnann, Leah Broussard, David Haase, and Zhiwen Zhao. ii TABLE OF CONTENTS Page LIST OF TABLES . vii LIST OF FIGURES . ix CHAPTER 1 NEUTRON ELECTRIC DIPOLE MOMENT OVERVIEW . 1 1.1 Physics Motivation . 1 1.1.1 Magnetic Monopoles . 1 1.1.2 Neutron Electric Dipole Moment (nEDM) Introduction . 3 1.1.3 Symmetry Violation . 4 1.2 Baryon Asymmetry . 5 1.3 History of nEDM Experiments . 8 1.4 Structure of This Thesis . 10 2 EXPERIMENTAL CONSIDERATIONS FOR THE SEARCH OF THE nEDM 13 2.1 SNS-nEDM Overview . 13 2.2 Production of UCN . 19 2.3 3He as Comagnetometer, Polarization Analyzer, and Detector . 20 2.4 Scintillation Detection in Superfluid Liquid Helium . 21 3 ROOM TEMPERATURE AND CRYOGENIC MEASUREMENTS ON PO- LARIZED HELIUM-3 . 23 3.1 Common Experimental Apparatus . 25 3.1.1 Cryostat . 25 3.1.2 Common Magnetic Coil Systems . 27 3.2 Design and Construction of a 3He Measurement Cell . 29 3.2.1 Cell Designs . 30 3.2.2 Measurement Cell Geometry and Coating . 37 3.3 Spin Exchange Optical Pumping Technique . 39 3.4 Nuclear Magnetic Resonance Technique . 43 iii CHAPTER Page 3.5 Room Temperature Measurements . 47 3.5.1 Calibrating Tip Angle. 50 3.5.2 Calculation of the Longitudinal Relaxation Rate T1 . 54 3.5.3 Room Temperature Results . 59 3.6 SQUID Overview and Motivation . 61 3.6.1 SQUID Principles of Operation . 61 3.6.2 SQUIDs: A Practical Approach. 64 3.6.3 SQUID System Design and Construction . 68 3.6.4 Cryoswitch Simulation . 71 3.6.5 Cryoswitch Resistance Measurement . 78 3.7 SQUID Measurements at 4 K . 79 3.7.1 SQUID Experimental Setup . 79 3.7.2 Noise Spectrum. 81 3.8 Conclusions . 85 4 SYSTEMATIC AND OPERATIONAL STUDIES APPARATUS . 86 4.1 PULSTAR Measurement Overview . 87 4.2 COMSOL Simulations and Physics . 91 4.2.1 Conductivity . 92 4.2.2 Black-Body Radiation . 94 4.3 COMSOL Simulation Models . 96 4.3.1 Actuator Arm . 97 4.3.2 Neutron Guide . 101 4.3.3 Heat Shields. 108 4.4 SQUID System Design . 111 4.4.1 Overview. 113 4.4.2 SQUID and Cryoswitch Control Techniques . 113 iv CHAPTER Page 4.4.3 Room Temperature Control Structure . 117 4.4.4 SQUID Mounting Location and Thermal Anchoring. 118 4.4.5 SQUIDs in the SOS Experiment . 125 4.4.6 Pick Up Coil Arrays . 128 4.5 Conclusions and Future Work . 130 5 LIQUID HELIUM SCINTILLATION . 132 5.1 LHe Scintillation Theory . 133 5.2 Overview of the Experiment . 134 5.2.1 Experimental Setup . 135 5.2.2 Experimental Procedure . 142 5.3 Problems and Solutions . 142 5.3.1 PMT Heat Sink to IVC . 144 5.3.2 Less Scintillation Light Than Expected. 148 5.4 Data Analysis . 151 5.5 Results . 156 5.5.1 Results For Temperature Range 0.61 K to 2.42 K . 156 5.5.2 Results For Measurements at 0.61 K . 158 5.5.3 Results For Temperatures Between 2.03 to 3.06 K Data . 160 5.6 Conclusions and Future Work . 162 6.