Cluster İons in Gas-Based Detectors

Abstract

Avalanches in gas-based detectors operating at atmospheric pressure and using Ar-CO<inf>2</inf> or Ne-CO<inf>2</inf> as drift medium produce in a first instance mainly Ar+, Ne+ and CO<inf>2</inf>+ ions. The noble gas ions transfer their charge to CO<inf>2</inf> in a few ns. A few ns later, the CO<inf>2</inf>+ ions have picked up CO<inf>2</inf> molecules, forming cluster ions, in particular CO<inf>2</inf>+·(CO<inf>2</inf>)<inf>n</inf>. Since the cluster ions are slower than the initial ions, the signals induced by ion motion are altered. The effect is shown to be present in constant-field detectors and TPC readout chambers, and is expected to affect devices such as Micromegas and drift tubes. © CERN 2015.