Abstract
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 40 m3 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.