Phase-changes and Feedthroughs: Hardware R&D for nEXO: PCB Feedthroughs, Thermal Control, and Testing

The origins of the universe are shrouded in mysteries that beckon discovery and hold the potential to answer profound questions we have been asking since the dawn of time, such as why we exist at all, or more specifically, why there is something rather than nothing. At the beginning of the universe, an asymmetry arose between matter and antimatter, leading to the matter-filled universe we observe today. However, the underlying reasons for this imbalance remain unexplained. Neutrinoless double beta decay is one of a few candidates for explaining this asymmetry. If detected, it would violate lepton number conservation and imply that neutrinos are their own antiparticles, known as Majorana particles. In this presentation, I describe hardware research and development supporting nEXO, a liquid-xenon time-projection chamber experiment at SLAC aimed at discovering neutrinoless double beta decay in the isotope xenon-136. A key factor in the detector's charge sensing is that the readout electronics operate in the liquid xenon. The goal is to develop a scaled-down test system to identify and address some issues faced by the nEXO detector. One challenge involves transmitting data from the sensor in liquid xenon, through a vacuum chamber, to ambient pressure at high speeds across interfaces. I report on the design and test of a vacuum feedthrough using a custom printed circuit board (PCB) which matches the differential impedance of standard LVDS lines, preserving data integrity across the interface. I will discuss this project as well as other hardware components that will facilitate nEXO's electronic testing at SLAC.