The ICARUS T600 Liquid Argon Purification System

AbstractThe ICARUS detector is a liquid argon time projection chamber with unique features that make it an ideal device to be used for several particle physics applications. After years of R&D activities, the ICARUS Collaboration proposed the construction of the T600 in strict partnership with industry to guarantee the necessary and viable scaling-up of the technology from prototypal dimensions to sized plants in order to study neutrino oscillations and matter stability in an effective way. The T600 represents the largest LAr detector (760 t LAr mass) ever realized. It was installed and successfully operated for 3 years inside the underground Gran Sasso Laboratory from May 2010 to June 2013. One of the most important issues for the success of the detector technology is the liquid argon purity. Purity requirements become stronger and stronger with the increase of the detector dimensions: for a plant of the ICARUS T600 size it is necessary to keep the residual electronegative impurity content to a level of the order of 0.1 parts per billion or better all over the argon volume during the whole detector run, thus allowing the ionization tracks, created by interacting particles inside LAr, to be transported with only slight attenuation along the drift path. In this paper we present the ICARUS T600 purification plant installed at Gran Sasso Laboratory and describe in details the solutions adopted for the LAr re-circulation and purification systems that permitted to reach impressive results in terms of LAr purity thus representing a milestone for any project involving LAr and developments at higher LAr mass scale