Novel method for in-situ drift velocity measurement in large volume TPCs: the Geometry Reference Chamber of the NA61/SHINE experiment at CERN

TL;DR

This paper introduces a low-maintenance, in-situ drift velocity measurement method for large volume TPCs, utilizing a Geometry Reference Chamber to achieve precise, real-time monitoring compatible with existing CERN detector systems.

Contribution

The paper presents a novel, cost-effective in-situ drift velocity monitoring technique using a Geometry Reference Chamber that integrates seamlessly with existing TPC electronics at CERN.

Findings

Achieved drift velocity monitoring with 0.1% precision within minutes.

Compatible with existing TPC electronics and adaptable to different particle fluxes.

Validated method in the NA61/SHINE experiment's large volume TPC system.

Abstract

This paper presents a novel method for low maintenance, low ambiguity in-situ drift velocity monitoring in large volume Time Projection Chambers (TPCs). The method was developed and deployed for the 40m^3 TPC tracker system of the NA61/SHINE experiment at CERN, which has a one meter of drift length. The method relies on a low-cost multi-wire proportional chamber placed next to the TPC to be monitored, downstream with respect to the particle flux. Reconstructed tracks in the TPC are matched to hits in the monitoring chamber, called the Geometry Reference Chamber (GRC). Relative differences in positions of hits in the GRC are used to estimate the drift velocity, removing the need for an accurate alignment of the TPC to the GRC. An important design requirement on the GRC was minimal added complexity to the existing system, in particular, compatibility with Front-End Electronics cards already used to read out the TPCs. Moreover, the GRC system was designed to operate both in large and small particle fluxes. The system is capable of monitoring the evolution of the drift velocity inside the TPC down to a one permil precision, with a few minutes of data collection.