Ph.d. degree
Weizmann Institute of Science (Israel), 2019

Eran Erdal

Supervisor: Prof. Amos Breskin and Dr. Shikma Bressler

Development of novel concepts of noble-liquid detectors for rare-event searches

Keywords:

• Noble liquid detectors (scintillation, ionization, double-phase)
• Micropattern gaseous detectors (MSGC, GEM, THGEM, RETHGEM, MHSP, MICROPIC, MICROMEGAS, InGrid, etc)
• Charge transport and multiplication in liquid media

Abstract:

Over the past two decades, noble-liquid detectors have come to play a leading role in several fields of physics requiring rare events detection. Typical examples are neutrino physics and dark-matter searches. Particle interactions in noble liquids result in light and charge signatures, which can propagate with little attenuation over large distances. This, along with their high density and scalability, turns them into a preferred option for experiments requiring large target masses with ultra-low background, event topology reconstruction, and high sensitivity to radiation-induced low-energy depositions. The leading noble-liquid detectors instruments are dual-phase Time Projection Chambers (TPC). While many TPC-signal readout technologies exist, there is concern regarding their scalability into the planned multi-ton size experiments.
The novel concept of the Liquid Hole Multiplier, LHM, the topic of this thesis work, was conceived as a single-element sensor for combined detection of radiation-induced ionization charges and scintillation light in a noble-liquid detection media. It suggests detection of ionization-electrons and UV-induced photoelectrons, through electroluminescence (EL) occurring in a gas bubble trapped under a CsI-coated perforated electrode immersed in the noble liquid.
The work done during the course of this Ph.D. aimed at deeper understanding of the mechanisms governing the operation and performance of the “bubble-assisted Liquid Hole Multiplier”. Most of the research has been carried out in liquid xenon (LXe). The first chapter in the results section establishes the experimental procedures performed in order to build and operate an LHM detector. It is followed by a comparative study of different electrode geometries in terms of light yield, energy resolution, timing resolution and relative photon detection efficiency. It is followed by a study of the photon detection efficiency and of radiation imaging using Silicon Photomultipliers. A first demonstration of LHM operation in liquid argon (LAr) is also presented. The last three chapters present new ideas related to the LHM detector concept: a double-stage LHM, an LHM with a vertical electrode and generation of EL between two parallel meshes.
Each chapter concludes with a short discussion. The final discussion summarizes all achievements, the remaining open questions to be investigated (along with some experimental suggestions) as well as some ideas for possible implementation in future Dark Matter experiments.
In addition, a second concept for charge multiplication, the cryogenic Resistive Plate WELL detector (RPWELL), has been suggested. The work however could not be completed due to difficulty in obtaining suitable resistive materials. Work in this context appears as an appendix to the thesis.