From ${}^{222}$Rn measurements in XENONnT and HeXe to radon mitigation in future liquid xenon experiments

While overwhelming evidence has been found for the existence of dark matter in our universe, its true nature remains a mystery. The XENONnT experiment has recently completed its commissioning and is now on the quest to solve this puzzle. This endeavor is threatened by the background caused by the emanation of ${}^{222}$Rn. In this work, a first estimate of the experiment's radon concentration will be given. Furthermore, the capabilities of the distillation-based radon removal system are demonstrated. For future liquid xenon (LXe) based experiments, the ${}^{222}$Rn-induced background needs to be suppressed even further. A novel radon mitigation technique using surface coatings has been investigated. Very promising reduction factors of more than three orders of magnitude have been achieved with electrochemically plated copper layers, applied to radium implanted stainless steel samples. Additionally, the interactions of alpha particles from ${}^{222}$Rn and electrons from ${}^{83m}$Kr have been studied in the Heidelberg Xenon (HeXe) time projection chamber (TPC). Field dependent measurements of the electron drift velocity as well as the charge and light yield are presented. For both, an emphasis was put on the regime of low drift fields, to improve the modeling and reconstruction in future LXe detectors.