Ion Mobility Studies Mixtures used in gas detectors

Abstract

Time Projection Chambers (TPC) allow a three-dimensional reconstruction of a particle trajectory or interaction that uses a sensitive gas as detection medium. This detectors have large volumes, and for an appropriate and improved operation it is essential to understand what is the detector’s behaviour if the gas parameters such as composition, pressure, temperature and type of gas are changed. In the scope of our participation in the RD51 collaboration/CERN, a common project was established with GSI Darmstag (Germany), Uluda˘g University (Turkey) and VECC (India) regarding the study of ion transport properties of relevant gas mixtures for ALICE TPC. With this in mind, we performed experimental ion mobility measurements, K0, for several gases and gas mixtures, namely for pure carbon dioxide, carbon dioxide mixtures (Ar-CO2, Ne-CO2, Ne-CO2-N2 and N2-CO2), pure nitrogen, nitrogen mixtures (Ne-N2), pure trimethylamine (TMA) and xenon-trimethylamine (Xe-TMA) mixtures. The results are presented for total pressures ranging from 4-20 Torr and for reduced electric fields (E=N) generally in the 10-25 Td range (6 to 60 Td in the case of pure gases), at room temperature. The IDC (Ion Drift Chamber) used to conduct the ion mobility studies was initially developed by P. N. B. Neves [4]. The techniques to perform the aforementioned studies are described in this report and make used of a Gaseous ElectronMultiplier (GEM) and a UV flash lamp to produce the ions. Also, a new, more practical and automatic method of analysis was developed in the form of a standalone application during this thesis program, which is also explained in this document. Finally, a redesign of the experimental system in order to improve it is suggested. Keywords: