Stability and detection performance of a GEM-based Optical Readout TPC with He/CF$_4$ gas mixtures

TL;DR

This study evaluates the stability and detection efficiency of a GEM-based optical readout TPC using He/CF$_4$ gas mixtures, demonstrating high efficiency and stable operation over 25 days, with some instability linked to lower CF$_4$ content.

Contribution

It provides the first long-term stability assessment of a GEM-based optical TPC with He/CF$_4$ mixtures, highlighting optimal gas proportions for stable and efficient detection.

Findings

High detection efficiency (>99%) with both gas mixtures.

20 ext% higher light yield for 60/40 mixture.

Stable operation maintained over 25 days.

Abstract

The performance and long term stability of an optically readout Time Projection Chamber with an electron amplification structure based on three Gas Electron Multipliers was studied. He/CF$_4$ based gas mixtures were used in two different proportions (60/40 and 70/30) in a CYGNO prototype with 7 litres sensitive volume. With electrical configurations providing very similar electron gains, an almost full detection efficiency in the whole detector volume was found with both mixtures, while a light yield about 20\% larger for the 60/40 was found. The electrostatic stability was tested by monitoring voltages and currents during 25 days. The detector worked in very stable and safe condition for the whole period. In the presence of less CF$_4$, a larger probability of unstable events was clearly detected.