Nome
Participation in the RD51 Collaboration at CERN

Código
CERN/FIS-INS/0013/2021

Entidade Beneficiária

LIP - Laboratório de Instrumentação e Física Experimental de Partículas

Sumário do Projecto

The principal aim of the CERN-based RD51 Collaboration is the development of advanced gas detector techniques for fundamental and applied science. It is particularly focused on development and implementation of micropattern detector structures (MPGD). This application represents a joint effort of three Portuguese research groups with extensive internationally recognized expertise in the development of novel particle detectors and techniques related to MPGDs as well as on studying the underlying physical processes. Founding members of RD51, the three institutions have a long standing and fruitful connection to the Collaboration resulting in both sound contributions to the RD51 program and the development and enrichment of national expertise and human potential. Following the previous work in the RD51, this proposal aims at contributing to WG1 (Technological Aspects and Development of New Detector Structures), WG2 (Common Characterization and Physics Issues), WG3 (Applications), in particular WG3.4 (Cryogenic Detectors for rare events), as well as WG4 (Software and simulation). We plan to focus on the following aspects. The investigation of electron emission from liquid xenon will contribute to the WG3.4 and WG2 packages. Emission of electrons from noble liquids is the fundamental process constituting the heart of all high-sensitivity low-background two-phase detectors. Yet, its mechanism is not well understood and a number of unexplained effects exist. We propose to measure the electron emission probability from LXe as a function of the electric field in a wide range of field values. In contrast with existing data, we propose to carry out absolute measurements by direct detection of the electric current and using a novel method, under development in our group, that allows to cancel most of the setup-dependent uncertainties. The results of this work will be of the utmost importance for a better understanding of the electron emission process from noble liquids and its practical use in the next generation of dark matter experiments with double-phase detectors, such as LZ and DARWIN, as well as in neutrino physics (e.g. DUNE). As our contribution to WG2, we also propose to measure the drift velocity of positive and negative ions in mixtures of gases with electronegative additives such as O2 and SF6, which are of significant importance for the development of next generation Negative Ion TPCs. The use of ion drift instead of electrons will allow to significantly suppress charge diffusion and thus improve track imaging capabilities of the detector. Based on the knowledge acquired with the previous setup, a new version, suitable also for negative ions, was built and tested for positive and negative ions. The results were compared with the published ones and are in good agreement, thus validating this technique. Some improvements of the ion chamber will be considered and the measurements will be supported by Monte Carlo simulation of ion transport using a dedicated code previously developed for positive ions and now planned to be extended to ions with negative charge (we will also contribute to WG4 with this work). Contribution to WG3 is extended with the COBRA_125 detector, applied here to neutron imaging. The versatility of this detectors will be exploited by equipping it with two sets of orthogonal electrodes, interconnected by a resistive line, allowing for 2D position reconstruction without the need of individual readout boards, as it is the case, for instance, of GEM foils. A stack of modules is typically used to increase the detection efficiency. Our approach has the advantage of reducing the overall material budget along the beam and, thus, minimizing the undesirable neutron scattering in the system components. The experimental studies we plan will allow us to verify our group’s recent simulations which showed that position resolution of neutron imaging detectors can be improved up to a factor of 8 by using thin neutron converter foils made of Boron and a pair of COBRA-like structures. Moreover, as our contribution to WG1 and WG2, we propose to implement and study new THCOBRA structures as well as to assess the potential of the combination THCOBRA+CCD for low energy  X-ray imaging, in particular. Also, we plan systematic studies of THCOBRA performance in Kr-Xe based mixtures with the aim of developing and building sealed detectors for such applications as X-ray fluorescence imaging and X-ray and CT imaging, with high detection efficiency, high gain and position resolution. Within the WG4, we propose to continue to develop software tools for modelling the complex physical processes taking place in MPGDs, namely, the tools based on Garfield++ and Degrad. We also plan to continue our work on intelligent methods (optimization and acceleration) for Garfield++/Ansoft/C++ based tools. This work will be done in a close collaboration with our partners from the RD51 Collaboration.

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