Speaker
Description
The bubble-assisted liquid hole-multiplier (LHM) concept, introduced several years ago, has been thoroughly investigated as a detection element for primary (S1) and secondary (S2) scintillation light detection in noble-liquid TPCs. The basic LHM idea relies on a CsI-coated perforated electrode immersed in the liquid, with a bubble of the liquid vapor trapped underneath. Radiation-induced Ionization electrons liberated in the liquid and S1 VUV-induced photoelectrons from the CsI photocathode are collected into the holes; as they cross the liquid-vapor interface into the bubble they generate intense electroluminescence (EL) signals.
In this contribution, we will discuss a new, simpler, concept – the bubble-free LHM. Here, the liquid-vapor interface lies above the perforated electrode, which now has CsI on its bottom face; the electrode is fully immersed within the liquid, with no bubble underneath. Ionization electrons created in the drift volume below the electrode and S1-induced photoelectrons emitted from the photocathode are focused into the holes from below and pass through them with nearly no losses. A strong field above the electrode (taking here the role of the “gate” in conventional dual-phase TPCs) ensures transmission of the electrons into the vapor phase, where they produce intense S1 and S2 EL signals. The main advantages of this concept are that single-VUV photon detection efficiencies can potentially be of the order of 20%, and that individual VUV photons generate large EL signals which cannot be faked by dark counts. Bubble-free imaging LHMs can therefore allow the use of VUV SiPMs or CMOS sensors, despite their high dark-count rates.
The talk will describe the basic principles of the new concept and summarize our current experimental results in LXe. These include photoelectron extraction efficiency into LXe, electron focusing efficiency into the LHM holes of both ionization electrons and photoelectrons, and the transfer efficiency of electrons towards the liquid-vapor interface. These results validate the new concept, providing a promising basis towards further studies and future applications.
