M.Sc. degree
Weizmann Institute of Science, Israel, 2015

Eran Erdal

Supervisor: Prof. Amos Breskin

Liquid Hole Multipliers — A new concept for large volume noble liquid time projection chamber

Keywords:

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

Abstract:

Direct dark matter detection is one of the most challenging fields in current experimental physics. Successful detection of dark matter particles will constitute a major step into the realm of physics beyond the standard model. Currently running experiments, dedicated to the search of Weakly Interacting Massive Particles (WIMPs) suggested by a variety of theoretical models, have already ruled out some models and set limits on others. The most sensitive among these experiments employ noble liquid targets (liquid xenon or liquid argon) as the detection medium and are operated in a dual-phase Time Projection Chamber (TPC) configuration. Since the sensitivity of these detectors scales as the mass of their noble-liquid target, increasingly larger detectors are being designed and deployed. However, to reach their ultimate sensitivity future noble-liquid detectors must grow to the multi-ton scale. The use of current detection concepts, may pose significant technological and economical challenges — calling for new developments.
This study focuses on further investigations of the innovative concept of Liquid Hole Multipliers (LHMs) as a potential solution for scaling noble-liquid detectors to the multi-ton regime. The idea consists of cascaded multiple UV-sensitive CsI-coated THGEM hole-electrodes, immersed in the noble liquid, and to multiply WIMP-induced photons and electrons via successive electroluminescence processes occurring within the THGEM holes. Previous studies conducted in our group have shown electroluminescence in the holes of a Thick Gaseous Electron Multiplier (THGEM) electrode immersed in liquid xenon - occurring at surprisingly low electric fields. In this work, we present our new understanding of the operation mechanism; we show that the electroluminescence occurs within xenon bubbles trapped below the electrode rather than in the liquid phase itself. We present a detailed study of the electroluminescence yield and achievable energy resolution of this new bubble-assisted LHM concept as a function of various parameters. We further discuss the identification of a "super-stable" state (corresponding to specific thermodynamic conditions) showing an exceptionally good energy resolution with alpha particles stopped in the liquid xenon. In addition, we also describe the design and commissioning of a new liquid xenon cryostat, dedicated to further systematic studies of the LHM concept and its bubble-assisted mechanism; results of its first operation period are presented. The potential application of the LHM to dark matter detection is discussed.