Final PhD Oral Examination (Thesis Title: “A linear Paul trap for barium tagging of neutrinoless double beta decay in nEXO”)
Physics and Astronomy
nEXO is the next-generation Enriched Xenon Observatory searching for neutrinoless double beta decay (0νββ) in ¹³⁶Xe. If observed, 0νββ will validate neutrino to be its own anti-particle and determine the absolute mass scale of the neutrinos. nEXO's sensitivity is limited by the background level. Barium tagging is the ultimate background rejection method using the coincidence detection of ¹³⁶Ba as the daughter nucleus.
A linear Paul trap (LPT) is needed for the barium tagging concept in nEXO or a future gaseous experiment. The theory of an ideal LPT were studied from the first principles to obtain semi-analytical solutions of the trapped ions and to validate a simulation method. Then simulations were done to optimize the design of a realistic LPT. A setup of the designed LPT was manufactured. Meanwhile, prototypes of key components of the LPT were built for the experimental developments. A prototype of the LPT's quadrupole mass filter (QMF) achieved mass resolving power m/Δm≈140, exceeding the requirement. A 3D printed prototype of the ion cooler demonstrated successful ion cooling, trapping and ejection. Based on the progress with the prototypes, improvements were made to the LPT design and have been included in the final setup. The final LPT will be installed between an RF funnel and a multi-reflection time-of-flight mass spectrometer for detailed study of barium ion extraction and identification from gaseous or liquid xenon.