Free electron lifetime achievements in Liquid Argon Imaging TPC

TL;DR

This paper reports on achieving a free electron lifetime exceeding 15 ms in liquid Argon TPCs, demonstrating advanced purification techniques that enable long drift distances for improved particle detection.

Contribution

It presents new purification methods and measurements of electron lifetime in a 120-liter LAr-TPC, enabling longer drift distances for liquid Argon detectors.

Findings

Electron lifetime of 21.4 ms observed, >15.8 ms at 90% C.L.

Residual Oxygen level around 15 ppt achieved.

Electron drift speed at 500 V/cm is 1.5 m/ms.

Abstract

A key feature for the success of the liquid Argon imaging TPC (LAr-TPC) technology is the industrial purification against electro-negative impurities, especially Oxygen and Nitrogen remnants, which have to be continuously kept at an exceptionally low level by filtering and recirculating liquid Argon. Improved purification techniques have been applied to a 120 liters LAr-TPC test facility in the INFN-LNL laboratory. Through-going muon tracks have been used to determine the free electron lifetime in liquid Argon against electro-negative impurities. The short path length here observed (30 cm) is compensated by the high accuracy in the observation of the specific ionization of cosmic ray muons at sea level as a function of the drift distance. A free electron lifetime of (21.4+7.3-4.3) ms, namely > 15.8 ms at 90 % C.L. has been observed over several weeks under stable conditions, corresponding to a residual Oxygen equivalent of about 15 ppt (part per trillion). At 500 V/cm, the free electron speed is 1.5 m/ms. In a LAr-TPC a free electron lifetime in excess of 15 ms corresponds for instance to an attenuation of less than 15 % after a drift path of 5 m, opening the way to the operation of the LAr-TPC with exceptionally long drift distances.