Measurements of ion mobility in argon and neon based gas mixtures

TL;DR

This paper reports measurements of ion mobility in argon and neon gas mixtures, crucial for simulating space charge effects in gaseous detectors like the ALICE TPC during high-rate operations.

Contribution

It provides new experimental data on ion mobility in various argon and neon-based mixtures, including effects of water content, aiding detector performance modeling.

Findings

Ion mobility decreases with increasing water content.

Measured ion mobilities vary across different gas mixtures.

Simulation validation confirms measurement accuracy.

Abstract

As gaseous detectors are operated at high rates of primary ionisation, ions created in the detector have a considerable impact on the performance of the detector. The upgraded ALICE Time Projection Chamber (TPC) will operate during LHC Run$\,3$ with a substantial space charge density of positive ions in the drift volume. In order to properly simulate such space charges, knowledge of the ion mobility $K$ is necessary. To this end, a small gaseous detector was constructed and the ion mobility of various gas mixtures was measured. To validate the corresponding signal analysis, simulations were performed. Results are shown for several argon and neon based mixtures with different $\textrm{CO}_2$ fractions. A decrease of $K$ was measured for increasing water content.